BUILDING PRACTICE
VOLUME 1
AC HAUPTFLEISCH(Editor)
PPR161SE
COPYRIGHT: THE SOUTH AFRICAN PROPERTY EDUCATION TRUST
First edition 1993
Revised edition 1999
Reproduced and printed by Print Production
Published by Technikon SA, Florida, Republic of South Africa
PREFACE TO THE SECOND EDITION
The first edition of the present text was published in 1993 on the initiative of the National
Council of the Institute of Property Practitioners of South Africa (IPPSA).
The objective of the first edition was to offer, in a condensed format, an introduction to
building practice that encompasses an industry overview, building processes, building
technology, building services and quantity surveying. The gratifying acceptance of that
edition, not only by the intended property practitioners but also other participants in the
building and property industries, resulted in the second edition having been comprehensively
revised, some chapters rewritten and others expanded to make it more user-friendly to a
wider body of students and practitioners.
A large number of sources were utilised in the preparation of the text. Use was made of
information obtained from the business fraternity, organised industry, individuals and
colleagues. These have been acknowledged in the text. Specific contributions were made
by the following persons, who are sincerely thanked for their valued input:
Chapter 1 was jointly written by HM Siglé and AC Hauptfleisch.
Chapters 2 to 4 were jointly written by HS Coetzee and AC Hauptfleisch.
Chapter 5 was written by HS Coetzee and AC Hauptfleisch (plumbing services), CE Cloete
(electrical services) and CR Bester (mechanical services).
Chapters 6 to 9 were written by AC Hauptfleisch.
Chapters 10 and 11 were written by JS Pienaar.
The editor accepts responsibility for errors and omissions which inevitably still remain.
AC HAUPTFLEISCH
January 1999
(i)
SERIES PREFACE
Resulting from the need expressed by various professional bodies in the property
industry for the rationalisation and promotion of formal education courses in property, the
South African Property Education Trust was established in 1988. Membership of the
Committee includes representatives of the following professional bodies:
The South African Property Owners Association (SAPOA)
The Institute of Property Practitioners of South Africa (IPPSA)
The Institute of Realtors of South Africa (IRSA)
The Estate Agency Affairs Board (EAAB)
The South African Council for Valuers (SACV)
The South African Institute of Valuers (SAIV)
After investigation of the various present and future needs of the property industry and the
existing courses which were being offered, it was recommended that course material should
be developed on a co-ordinated basis, to be utilised by tertiary educational institutions for
formal training in property and to be financed by a Trust established for this purpose.
The South African Property Education Trust was established in April 1990. The object of
the Trust is, inter alia,
"The establishment of a special fund in the Republic for the sole purpose of receiving
donations to be used exclusively
(i) for the promotion of adult education or vocational training of persons who areconcerned with the
immovable property sector of the South African economy; and
(ii) for the benefit of any University or Technikon or College for the furthering of theacquisition of
knowledge pertaining to the immovable property sector of theSouth African economy."
Dit sluit die opstel van boeke of ander opvoedkundige materiaal in sowel as die rasionalisering
en/of koördinering en/of verspreiding van opvoedkundige materiaal.
Hierdie studiegids
The hope is expressed that the material will contribute to enhancing the professionalism
of practitioners in the property industry.
Prof CE Cloete
Department of Quantity Surveying and Construction Management, University of Pretoria
CHAIRMAN, NATIONAL PROPERTY EDUCATION COMMITTEE
(ii)
CHAPTER 10:
CHAPTER 11:
TABLE OF CONTENTS
VOLUME 1
THE STRUCTURE OF THE BUILDING AND PROPERTY
INDUSTRY IN SOUTH AFRICA
SOIL MECHANICS AND BUILDING FOUNDATIONS
BUILDING CONSTRUCTION
BUILDING COMPONENTS AND FINISHES
BUILDING SERVICES
VOLUME 2
ENVIRONMENTAL CONTROL IN BUILDINGS
PEST CONTROL IN BUILDINGS
TOTAL QUALITY MANAGEMENT
MAINTENANCE
ESTIMATION OF BUILDING COSTS
PROCUREMENT FOR BUILDING PROJECTS
(iii)
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77
99
KEY TO ICONS
The following icons are used throughout
(NB
study guide to indicate specific functions:
LEARNING OBJECTIVES
DEFINITION
EXAMPLE
NB/TAKE NOTE
SELF-EVALUATION
(iv)
THE STRUCTURE OF THE
BUILDING AND PROPERTY
INDUSTRY IN SOUTH AFRICA
CONTENTS
LEARNING OBJECTIVES
1.1
1.1.1
1.1.2
1.1.3
1.2
1.2.1
1.2.2
1.3
1.3.1
1.3.2
1.3.3
1.4
1.4.1
1.4.2
1.5
1.5.1
1.5.2
1.5.3
INTRODUCTION
The building industry
The property industry
Definitions
STATISTICAL DATA
Building and civil engineering work at nominal prices
Building work at fixed (real) 1996 prices
PRODUCTION PROCESS
Inputs
Conversion process
Outputs
BUILDING CONTRACTS AND BUILDING PROCESSES
Building contracts
Types of building processes
THE EMPLOYER, BUILDING CONTRACTOR AND
SUBCONTRACTORS
The employer
The building contractor
Subcontractors
QUESTIONS FOR SELF-EVALUATION
REFERENCES
PAGE
2
2
2
2
2
3
4
6
7
7
7
8
8
8
9
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26
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LEARNING OBJECTIVES
The objectives are to introduce the student to the operation of the building
and property industry in general, to identify the building processes in use,
and the role of the parties involved in those processes.
After completion of this module the student should be able to distinguish
between various building processes and contractual arrangements which
can be used to execute building work.
1.1 INTRODUCTION
1.1.1 The building industry
From the outset, a distinction should be made between the building industry and
the construction industry. In certain countries no distinction is made between
these industries, while in other countries they are referred to as “light” and “heavy!
construction. The following definitions and information will indicate that these
two types of construction are regarded as different industries in South Africa.
1.1.2 The property industry
The property industry is collectively the owners and managers of fixed property
which mainly consist of buildings. Engineering works such as tollroads will most
probably play a major role in the future.
1.1.3 Definitions
The following definitions are grouped hereunder to provide the reader with general
information while others are given later where the relevant term is discussed:
The architect is the designer of the proposed building in accordance with the
requirements of the employer and usually acts as the principal agent for the
employer in the administration of the building contract and the execution of the
building work contracted for.
The building industry is that operational sector which provides buildings to the
requirements of an employer by making use of the building professions, main
contractors, subcontractors and a variety of allied resources,
The building process is a certain procedure with an established pattern which
is generally accepted by the parties involved and which aims to erect a building
to the optimal satisfaction of the employer.
The civil engineering construction industry is that operational sector which
provides engineering structures (dams, roads, bridges, pipelines, etc.) to the
requirements of a client by making use of consulting engineers, civil contractors,
subcontractors and a variety of allied resources.
The employer (or client) is that party who initiates and finances the building
process in order to erect a building that will meet his requirements and that will
belong to him.
The engineer (structural, mechanical and electrical) designs the various
engineering services in accordance with the requirements of the employer and
usually acts as agent of the employer in the administration of the contract and
the execution of the building and/or engineering work contracted for.
The main contractor is the party who is contractually bound to the employer to
provide all labour and material necessary for the erection of the building in such
a way that it will meet the employer's requirements.
The parties to the building process are the employer, architect, quantity Surveyor,
structural, mechanical and electrical engineers, main contractor and subcontractors
as well as any other party or body that makes an active contribution to the erection
of a building.
The quantity surveyor as an agent of the employer estimates the cost of the
building work during the design stage and during erection, draws up contract
documents and calculates the final cost of the work at completion.
The subcontractor is the party who is contractually bound to the main contractor
to provide all labour and material necessary for the erection or installation of a
specialised part of the building in such a way that it will meet the requirements
of the employer and the main contractor.
1.2 STATISTICAL DATA
The building industry represents a major portion of the total fixed annual investment
in the building industry, civil engineering construction industry, transport, equipment
and machinery. Comprehensive data is provided annually by the South African
Reserve Bank (SARB) and by the Building Industries Federation South Africa
(BIFSA). The following nominal and real (fixed) data provides an overview of the
five year period, 1993-1997:
1.2.1 Building and civil engineering work at nominal prices(Source: SARB, BIFSA)
Table 1.1(a) Residential buildings (Rm)
Year
1993
1994
1995
1996
1997
952
988
978
1 088
1 208
Public
corporations
24
29
6
4
4
Total:
Public
976
1 017
984
1 092
1 212
Table 1.1(b) Non-residential buildings (Rm)
Year
1993
1994
1995
1996
1997
1 524
1 764
2 156
514
417
563
2 038
2 181
2 719
Table 1.1(c) Civil engineering work (Rm)
Year
1993
1994
1995
1996
1997
1 533
1 656
6 735
7 203
7 396
9522
10 586
Public
corporations
299
391
Public
corporations
1 234
776
1 140
1 354
2 282
Total:
Public
1 832
2 047
Total:
Public
7 969
7 979
8 536
10 876
12 868
Total:
Private
6 215
6 906
7 700
8 505
9 137
Total:
Private
5 496
5 787
6 051
7 454
8 458
Total:
Private
2 282
2 726
3 321
3 338
4 081
Grand
Total
7 191
7 923
8 684
9 597
10 349
Grand
Total
7 328
7 834
8 089
9 635
11 177
Grand
Total
10 251
10 705
11 857
14 214
16 949
Table 1.1(d) Total: Residential, non-residential and civilengineering (Rm)
Year
1993
1994
1995
1996
1997
9 220
9 847
9 898
12 374
13 950
Public
corporations
1 557
1 196
1 660
1 775
2 849
Total:
Public
10 777
11 043
11 558
14 149
16 799
Total:
Private
13 993
15 419
17 072
19 297
21 676
Building and civil engineering work as a % of the total for 1997:
Grand
Total
24 770
26 462
28 630
33 446
38 475
Table 1.2 Residential and non-residential work as a % of totalbuilding work (1997) (Rm)
Type of
investment
Residential
Non-residential
1 208 (12%)
2 156 (19%)
3 364 (15%)
4 (0%)
563 (5%)
567 (3%)
9 137 (88%)
8 458 (76%)
17 595 (82%)
10 349 (48%)
11 177 (52%)
21 526 (100%)
Table 1.3 Building and civil engineering work as a % of totalwork (1997) (Rm)
Type of
investment
Building
Civil
Public sector
and corporations
3931
12 868
16 799
(18%)
(76%)
(44%)
Public
corporations
17 595
4 081
21 676
(82%)
(24%)
(56%)
21 526
16 949
38 475
(56%)
(44%)
(100%)
1.2.2 Building work at fixed (real) 1996 prices (Source: SARB, BIFSA)
Table 1.4 Building work at fixed 1996 prices (Rm)
Residential
Investment
Non-residential
Investment
Investment in the Public
Building Industry sector
Civil
Industry
Investment
in the total
Construction
Industry
1993
1994
1995
2%
1996
1997
R Value R1,270 R1,226 R1,090 R1,092 R1,147
% Change -9%-3% - 11%0% 5%
R Value R8,026 R8,252 R8,402 R8,505 R8,495
% Change-1%
3%1%0%
R Value R9,296 R9,478 R9,492 R9,597 R9,642
% Change-2%
2%
0%
1%0%
R Value R2,365 R2,444 R2,222 R2,181 R2,546
% Change -4%3%
-9%-2% 17%
R Value R7,112 R6,932 R6,603 R7,454 R7,817
% Change -8%-3%
-5% 13%5%
R Value R9,477 R9,376 R8,825 R9,635 R10,363
% Change-7%
-1%
-6%
9%8%
R Value R3,635 R3,670 R3,311 R3,273 R3,693
% Change-6%
1% -10%-1% 13%
R Value R15,138 R15,184 R15,006 R15,959 R16,312
% Change-4%0%
-1%
6%2%
R Value R18,773 | R18,854 R18,317 R19,232 R20,005
% Change-4%
0%
-3%
5%4%
R Value R10,315 R9,592 R9,310 R10,876 R12,050
% Change -9%-7%
-3%
17%11%
R Value R2,936R3,260R3,617 R3,338 R3,912
% Change -17%11%
11%-8% 17%
R Value R13,251 R12,852 R12,927 R14,214 R15,962
% Change -11%-3%1% 10% 12%
R Value R13,949 R13,263 R12,621 R14,149 R15,743
% Change-8%
-5%-5% 12% 11%
R Value R18,075 R18,444 R18,622 R19,297 R20,224
% Change -6%2%
1%
4%5%
R Value R32,024 R31,707 R31,243 R33,446 R35,967
% Change -7% -1% -1%7%8%
% Change = Year-on-year real percentage change
1.3 PRODUCTION PROCESS
The building industry in South Africa is a fragmented production process where
each new project involves the establishment of a new "factory” usually with a new
group of participants. The process by which buildings are erected is described as
a "building process”, which is clearly a common production conversion process.
The process involves inputs, conversion/processing and outputs.
Inputs
Conversion/
processing
Figure 1.1 Conversion process
Outputs
1.3.1 Inputs
The inputs for the conversion process comprise the normal economic production
factors of the industry, these being: Capital: Provided by the employer for the land and buildings, while
the
professional consultants and contractors require operating capital within
their own organisations.
Human resources: Human resources are provided by the professional
consultants and all the contracting parties.
Raw material: The basic raw materials are mainly obtained by the main
contractor and subcontractors from manufacturers and dealers.
Entrepreneurship: This production factor is present in fragmented form,
ranging from the employer to the professional consultants and the main and
subcontractors. Entrepreneurship is initiated by the employer when hegives the brief to erect a building.
The erection of buildings is a complex process which requires a diversity of inputs,
as well as considerable expertise in managing these inputs.
1.3.2 Conversion process
The conversion process is manifested in a building process. The selection of
the type of process rests with the employer and is discussed later.
The various building processes are embodied contractually in a large number of
building contracts, of which the ost important are discussed later.
1.3.3 Outputs
The output of the conversion process is a completed building that meets the
requirements which the employer has set as part of the inputs.
1.4 BUILDING CONTRACTS AND BUILDING PROCESSES
1.4.1 Building contracts
A building contract is an agreement in terms of which one party, called the
building contractor, agrees to perform building or engineering work for another
party, called the employer, at a fixed remuneration or an agreed basis of
remuneration.
Requirements for a legal contractThe agreement must be entered into in earnest and there should be a
valid reason for entering into it.
There must be consensus.
The agreement must be legal (agreement to commit an offence is illegal).
Execution of the agreement must be possible.
If the law requires certain formalities, these must be met. Building
contracts may be entered into verbally but this is strongly discouraged.
The parties must be competent to enter into a contract. The following
persons for instance are incompetent: Minors
Women married in community of property before 1 November 1984
Insane persons
Unrehabilitated insolvent persons
Concluding a building contract
Contracts are concluded by one person making an offer and the other
accepting it. This must be distinguished from an invitation to negotiate where
a contract is only concluded once negotiations have been completed.
Building contractors are invited by or on behalf of the employer to make an
offer based on certain documents. Each contractor's tender is thus an offer
and when it is accepted a contract is concluded.
An invitation to tender may in certain cases be preceded by an invitation to
contractors to submit their names for inclusion in a tender list. This usually
occurs when the building is of a complicated nature and/or very large. An
invitation to tender can be put to a selected group of contractors or by means
of an open invitation in the press.
It is usually stated in advertisements that the lowest or any tender (offer) may
not necessarily be accepted.
Although a written agreement is not always necessary or a legal requirement
to conclude a building contract, it is advisable due to the complexity and high
cost of a building project.
After the quantity Surveyor has checked the priced bills of quantities as well
as the contractor's financial status, he makes a recommendation to the
architect who in turn makes a recommendation to the employer.
If the employer is satisfied the parties enter into a written agreement. The
contract documents consist of various sections which may include the following
depending on the type of contract: Contract drawings which indicate the work that has to be done
Specifications which set out in words the quality of materials and
workmanship (usually included in the bills of quantities)
Priced bills of quantities
Schedule of model preliminaries
Agreement and schedule of conditions of building contract
The tender form
Explanatory letters
Tender qualifications
1.4.2 Types of building processes
Building processes in South Africa cannot be categorised in any simple way due
to the overlap and combination of methods used in practice. The aim is to identify
those building processes which can be regarded as representative of the whole.
The classification is therefore very general and does not attempt to give a detailed
description of all the alternatives.
(a) Traditional building process
The traditional building process is a typical fragmented serial process in which the
employer employs the professional consultants and the main contractor - the
main contractor usually after calling for competitive tenders. After the contract
has been awarded, the main contractor himself appoints subcontractors and he
also appoints nominated and/or selected subcontractors after consultation with
the architect.
The process as a whole is fragmented and each party to the building process
carries out a separate portion of the whole process. The architect acts as the
principal agent of the employer and is responsible for the management of the
process.
Contractual agreements are entered into between the main contractor and the
employer and between the main contractor and the subcontractors. The
professional consultants are not contracting parties as far as the building work is
concerned but they have in fact contracted to provide a professional service to
the employer. Typically an architect, a quantity Surveyor, a structural engineer, a
mechanical engineer, an electrical engineer, a main contractor, subcontractors and
nominated and/or selected subcontractors are involved. In certain cases other
consultants are also involved such as acoustic consultants, landscape architects,
town and regional planners, security specialists and others.
This process culminates in a building contract with (or without) bills of quantities.
In the private sector the Principal Building Agreement of the Joint Building
Contracts Committee (JBCC) or the so-called "white form” contract document is
generally used. Various other standard contract forms are also prescribed by
employers in the public and private sector.
The traditional building process as it is commonly found in South Africa may be
defined as follows:
The traditional building process is a serial process by which the employer
obtains a stand for development and usually appoints an architect, a quantity
surveyor, consulting engineers and various other professionals to prepare
documentation for tender purposes and the execution of the building work by the
successful main contractor and his subcontractors, with the architect acting as
the principal agent of the employer.
Figure 1.2 illustrates the flow of the operations vertically and the inputs of the
various parties horizontally. Figure 1.3 illustrates the contractual commitments
and lines of authority that are established.
Design
Tender documents
Tender
Adjudication
of fender
Building
Final account
Completed building
Financial advisors
(Quantity Surveyor)
Architect
Structural engineer
Electrical engineer
Mechanical engineer
Quantity Surveyor
Landscape architect
Land surveyor
Other
Quantity Surveyor
Architect
Engineers
Quantity Surveyor
Architect
Main contractor
Subcontractors
Dealers
Town and regional planner
Municipal zoning
regulations and other
restrictions on design
Subcontractors
Dealers
Supervision:
Architect
Engineers
Clerk of works
Inspectors
Figure 1.2 Flow diagram of the traditional building process
Contractual
commitments
Lines of authority
Nominated/selected
subcontractors
Nominated/selected
subcontractors
Suppliers to
nominated/selected
subcontractors
Suppliers to
nominated/selected
subcontractors
Figure 1.3 Contractual commitments and lines of authority inthe traditional building process in South
Africa
The following advantages and disadvantages are characteristic of the traditional
building process. The comments below refer to contracts with and without bills
of quantities:
Building contract with bills of quantities
This procedure is implemented when there is enough time available to produce
comprehensive tender documentation.
One of the major aspects of this type of contract is the bill of quantities which
can be defined as follows:
Bills of quantities are documents in which all the labour and material
needed to erect a building is accurately given in prescribed units according (D.
to a standard method and the circumstances in which it is to be built is fully
described.
Working drawings and specifications are usually completed before
bills of quantities can be produced and tenders are called for and
the building process is thus based on completed documentation.
Competitive tenders, based on identical information, especially in
respect of quantities and the amount of work that has to be
performed, are called for. Theoretically a price differentiation thus
indicates the efficiency of the various tenderers. The correctness
of the quantities in the bills of quantities is the employer's risk and
tenderers need not concern themselves about the quantities.
The rates as reflected in the bills of quantities serve as a reliable
basis for cost adjustments resulting from variations to the contract.
Monthly payments to the contractor are made on the basis of the
amount of work completed and the rates in the bills of quantities.
Final accounts are relatively easy to settle as rates for variations
are already known at tender stage.
Costs are lower as the bills of quantities are prepared by the quantity
surveyor and not by each tenderer.
Members of BIFSA prefer to tender for projects with bills of quantities
as this forms a basis for tender adjudication.
Projects with bills of quantities attract a large number of competitive
tenderers due to the lesser amount of work for the tenderers.
Priced bills of quantities provide complete information for financial
analysis and control.
Disadvantages: It is not absolutely certain what the final building costs will be.
Quantities given in the bills of quantities as provisional may differ
from the final measurement. Tenders for specialist work to be
performed by nominated/selected subcontractors are mostly not
called for at tender stage of the main contract and differences
between the provisional sum allowed in the bills of quantities and
the actual cost may occur which in turn will affect the final cost of
the contract.
It takes time to prepare bills of quantities and this involves “visible"
quantity surveying costs.
Building contract with provisional bills of quantities
This procedure is usually followed when a project is so urgent that tenders
have to be called for before the working drawings, specifications and accurate
bills of quantities can be completed. Provisional in stead of accurate quantities
are included in the bills of quantities to a more or lesser degree depending
on the state of completeness of the working drawings and specifications.
All the advantages that apply to accurate bills of quantities also
apply in this case.
Disadvantages: Tender information is based on incomplete working drawings and
specifications and the employer therefore runs the risk that final
quantities may differ appreciably from those in the provisional bills
of quantities and hence affect the final building cost.
Because of the fact that the design of these building projects is not
completely thought through they are characterised by numerous
variations.
The employer, professional consultants and the contractor are
subject to time restraints, communication gaps and rapid decisionmaking which is not conducive to
saving of costs. The risk factor
for all the parties increases.
Building contract with a schedule of rates
This procedure is followed when a project is so urgent that tenders have to
be called for at a stage when there is not enough information available for
even producing provisional bills of quantities. A schedule of rates which is
basically a bill of quantities without quantities is used as a tender document.
Tenders can be called for at a very early stage and basic rates are
available to determine the costs while the work is in progress.
Variations are also based on predetermined rates.
Except for the lack of accurate bills of quantities all other tender
documentation may still be of a high standard.
Disadvantages:
All the disadvantages that apply to provisional bills of quantities
contracts also apply here.
It is difficult to adjudicate tenders as there are no quantities to
determine the relative effect of the different rates.
The final building cost is not known at tender stage.
Proper financial analysis and cost control are almost impossible
due to the lack of completed working drawings, specifications and
quantities.
The administrative cost increases for all parties concerned.
Building contract without bills of quantities (lump sum contract)
This type of contract is mainly used on smaller building projects and tenders
are based on working drawings and specifications only (no bills of quantities).
Working drawings and specifications are completed before tenders
are invited and the building process is based on complete
documentation (no bills of quantities).
The employer is usually certain what the final cost will be before
the building operations start. Provisional sums, however, can
influence the final cost just as is the case with contracts with bills
of quantities.
Tenderers prepare their own "builders quantities” which may result
in a time saving against the time taken by the quantity Surveyor to
prepare accurate bills of quantities and there is no visible expense
related to this (see disadvantages hereafter).
Provisional sums can be included in the specification.
**
Disadvantages: There is no basis for the adjustment of building costs if variations
Occur.
No simple basis for monthly payments or cost control exists.
All tenderers must prepare their own bills of quantities to determine
their tender price. This cost is eventually reflected in the tenderer's
overhead costs.
Members of the Building Industries Federation South Africa (BIFSA)
will only tender in competition for a project up to an amount of
R500 000 or for dwellings up to 500 square metres (irrespective of
price) without bills of quantities.
Cost-plus building contracts
Cost-plus building contracts are usually entered into if there is no time for
any negotiations or tender and are to a great extend based on mutual trust.
The “plus” refers to a percentage or an amount that will be added to the
actual cost of the project, hence the name “cost-plus”.
It is the quickest possible way of getting building work started.
Disadvantages:
There is little incentive for the contractor to keep the costs as low
as possible, especially where the “plus” is coupled to the "cost" as
a percentage.
Defining and application of the "cost" and "plus" elements create
problems.
Final building costs are typically higher than that for other contracts.
It is difficult to separate the cost involved in correcting mistakes
incurred by the contractor from actual costs.
Final building costs are not known which inhibits decision-making.
Financial analysis and control is almost impossible for any of the
parties.
Contract documentation is not always comprehensive and complete.
Certain of the disadvantages of cost-plus building projects can be
eliminated by agreeing on a target or ceiling figure with a sharing of the
difference between the target or ceiling figure and the actual final cost
between the employer and the contractor. It is, however, still a high risk
arrangement for the employer. Even though cost-plus contracts may
initially appear attractive these contracts cause so much administrative
work and disputes that they are in fact frequently unattractive to
contractors.
(b) Package, design-and-build and turn-key contracts
There are no generally accepted definitions, standard tender conditions and
standard building contracts in respect of package contracts and consequently there
is a great deal of confusion regarding the terminology used. In general it may be
said that the word “package” refers to a large number of building processes that
differ in detail from each other but have the common purpose of providing an
employer with a complete or one-stop service.
This service is mainly provided by main contractors, but also by people who are
not contractors but who wish to co-ordinate packages and sell them at a profit,
or obtain a project management contract for the co-ordinator or possibly obtain
an appointment as one of the members of the professional team.
Generally the term “package" seems to refer to commercial and larger housing
projects, while "design-and-build” refers to individual houses and "turn-key"
generally to industrial projects. On the basis of this distinction, “package" contracts
as a generic type and "turn-key" as a specific application are defined below and
the advantages and disadvantages of each are identified.
Package and design-and-build contracts
Package contracts are offered by the co-ordinator (usually a main contractor)
to a potential employer at a specific price that includes all professional
services and a building contract and sometimes also the site, equipment and
commissioning.
Figure 1.4 illustrates the flow of operations vertically and the inputs by the
various parties horizontally. Figure 1.5 illustrates the contractual commitments
and lines of authority that are established.
NB
Main contractor
Compiler of package
Design
Building
Completed building
Professional services without
executive powers
Financing
Main contractor
Subcontractors
Dealers
Figure 1.4 Flow diagram of a package building contract
Contractual
commitments
Lines of authority
Private consultants
or
consultants employed
by the
main contractor
Private consultants
or
consultants employed
by the
main contractor
Figure 1.5 Contractual commitments and lines of authorityin the package building contract in South
Africa
It is a simple solution for the employer's requirements, especially if
the employer is not involved in building operations on a regular basis.
The employer is freed from the responsibility of appointing various
professional consultants and entering into numerous contracts with
a wide range of implications.
The process is very rapid. Communication channels are short and
concentrates on management activities and buildings are usually
ready earlier than in serial building projects where various parties
are involved.
‫܀‬
Even though the value of packages are difficult to measure, there
are nevertheless some – especially those producing housing and
industrial buildings – that may be to the financial advantage of
employers (those with guaranteed returns and/or collateral
assistance)
In cases such as individual housing, packages that offer a total
service (even finance) are sometimes the only possible solution for
the employer's problems which he often cannot deal with on a
fragmented basis.
In those cases where financing forms part of the package it is
frequently the only and most effective way by which the employer can
obtain financing. Contractors provide various types of guarantees to
financial institutions which undertake to provide financing for their
clients.
Disadvantages:
The disadvantages of building contracts without bills of quantities
also apply here.
The employer does not have an independent team of professional
consultants and stands contractually on his own. He may find
himself in an unenviable position if problems arise. Legal costs
and expert advice in such cases are expensive.
It is difficult to determine whether the employer is getting the best
value for his money as there are no comparative prices. Detailed
specifications and drawings are usually not available, which further
complicates the issue of value.
The contractual relationship between the employer and the contractor
depends on good faith to a greater extent than in the traditional
building process.
Turn-key contracts
Turn-key contracts are offered by a co-ordinator (usually a main contractor)
to a potential client at a predetermined price that includes the site, professional
services, a building contract, financing, equipment and commissioning.
The advantages of package contracts also apply to turn-key projects.
The employer's responsibilities are determined by a single contract.
Disadvantages:
The disadvantages of package contracts, relative to the total service
offered, are also relevant here.
(c) Project and construction management
The concepts “project management" and “construction management are frequently
used confusingly in South Africa, mainly because these building processes,
particularly construction management, are not as commonly used as for example
in the United States of America (USA). The confusion is aggravated by the lack
of standardised definitions and distinctions between the two concepts.
The terms are sometimes used loosely with reference to the process which strictly
speaking, in South Africa, mainly applies to project management. The confusion
arises from the fact that construction management is still virtually unknown in
South Africa whereas project management, on the other hand, has been used in
the manufacturing industry for a considerable time and has over the last decade
become more prevalent in the building and civil engineering construction industry.
Project management is however in the process of building up a sound reputation
in the building and civil engineering construction industry.
Construction management normally only finds application when large and/or
very complex projects are involved. The rational being that the risk of the client
is reduced if he contracts directly with numerous specialised contractors and
replaces the main contractor with a construction manager. The empowerment of
emerging contractors through the division of projects into many small contracts,
which is presently taking place in South Africa, will in all probability stimulate the
development of a local construction management process which might grow
rapidly, supported by “mini-bills of quantities” for each trade, and even the
breaking-up of trades.
Project management, which basically involves the formalisation and management
of the employer's requirements, can either be undertaken internally by the employer
or by private independent consultants. Project managers are found in the service
of employers, especially institutional investors and corporate property developers,
while there are a few private project managers in the market who offer their
services as an extension of the private sector employer's services. To some
degree, the task of the project manager is to offer a management service that
involves both the normal duties of an employer and some of the duties of the
architect or others as principal agent of the employer.
Project and construction managers are paid on a commission basis for their
services and in practice, their liability does not seem to differ appreciably from
that of other building professionals.
Project management and construction management in the South African context
are defined below to clarify their meaning.
Project management is a building process for which the employer appoints
an agent or employee at a professional fee or a salary to manage the whole
process for the erection of a building in such a way that the employer's
requirements in terms of aesthetics, quality, cost and time are met.
Construction management is a building process for which the employer
appoints a manager at a professional fee or a salary to manage the entire
production process on site from beginning to end by using specialist
contractors.
Figures 1.6 and 1.7 show the contractual commitments and lines of authority
that are established in project management and construction management
respectively.
Project manager
Contractual
commitments
Project manager
Lines of authority
Nominated/selected
subcontractors
Nominated/selected
subcontractors
Suppliers to
nominated/selected
subcontractors
Suppliers to
nominated/selected
subcontractors
Figure 1.6 Contractual commitments and lines of authority in theproject management building process
in South Africa
Project manager
Construction manager
Specialist
contractors
Contractual commitments
Project
Manager
Construction
manager
Specialist
contractors
Lines of authority
Suppliers to specialist
contractors
Suppliers to specialist
contractors
Figure 1.7 Contractual commitments and lines of authority inthe construction management building
process
***
Advantages of project managementThe total development cost may be lower because certain
traditional
professional services and sometimes a main contractor are not required.
Central management with unity of authority increases efficiency and
effectiveness.
Technical, financial and programming skills are utilised fully from the
conceptual stage.
The employer's direct involvement is reduced to a minimum, which saves
his time.
Controlled "fast track” construction where design, documentation and
building work take place concurrently is possible.
The professionals used have no split responsibility. The architect both as
principal agent and designer in other types of contracts is an example
hereof.
There is greater specialisation with less fragmentation for the professions
individually and the project as a whole.
Efficient time and cost control can be applied on a formal basis.
The advantages of good management are to the benefit of all parties, but especially to the employer.
Disadvantages of project managementThe employer has an additional commitment with respect to
professional
fees, which is not necessarily compensated for by visible or proven
savings.
The employer enters into a greater number of contractual commitments
with potentially more problems. The professions have less direct contact with the employer.
Construction management can be applied on any project where the nature of
project dictates that a construction manager should be used. The advantages
and disadvantages listed below, therefore specifically reflects application in
South Africa.
Advantages of construction management
When a project is so large and/or complicated that there is a real risk
involved to place the entire contract in the hands of one main contractor,
then the employer can spread the risk by contracting directly with a
specialist, replacing the main contractor with a construction manager who
takes a professional responsibility and not a normal contractual risk.
An employer obtains a flexible process whereby social-economic issues
can be addressed, for instance by breaking up a larger project into
numerous small contracts whereby more small (emerging) contractors
are afforded the opportunity to partake in such a project, contracting
directly with the employer and thus not as subcontractors to a main
contractor.
Disadvantages of construction managementThe employer enters into a very broad spectrum and large
number of
smaller contracts. The advantage of one main contractor taking full
responsibility is lost.
Managing numerous small direct contractors and blending them into the
project as a whole is extremely difficult without a main contractor taking
full responsibility
Gaps are inevitably found between a large number of small contracts,
which would normally be filled by a main contractor, and which now
becomes the risk of the employer.
1.5 THE EMPLOYER, BUILDING CONTRACTOR ANDSUBCONTRACTORS
1.5.1 The employer
Employers (investors) are generally either private sector employers or public
sector employers. The operation of each group is typical and is determined by
the source of finance for the particular building. The private sector employs risk
capital, consisting of its own capital and loan capital, whilst the public sector
employs funds obtained from taxation. The various types of employers may be
classified as follows:
Private sector
Private persons
Close corporations
Companies
Churches
Insurance companies
Pension funds
Banks and other financial institutionsTrusts, etc.
The investment of the private sector in property is mainly aimed at profit
making through returns on rent, capital growth and at providing a hedge
against inflation.
Other reasons for the investment in property may not involve the profit motive
or may be to make a very small profit to satisfy a particular need that cannot
necessarily be quantified, for example the erection of churches, recreation
centres, sporting facilities, private dwellings and private schools. Employers,
building owners and other role-players in the private sector established an
association called the South African Property Owners Association (SAPOA).
‫܀‬
Public sector
(a) Central government
Housing
Office buildings
Industrial buildings (printing works, etc.)
Infrastructure (police stations, defence, etc.)
Engineering works (roads, dams, bridges, etc.)
(b) Provincial governmentsOffice buildings
Schools
Hospitals
Workshops
Recreation faci nd resorts
Engineering works (roads, dams, bridges, etc.)
(c) Local authorities
Housing
Office buildings
Workshops
Libraries
Clinics
Basic servicesEngineering works (roads, dams, bridges, etc.)
(d) Regional services councils
Housing
Workshops
Basic services
Infrastructure
(e) Universities and technikons
Educational facilities
Research complexes
Sport facilities
Housing
(f) Public corporations, public companies belonging to the state or understate control and semigovernment institutions
Office buildings
Research complexes
Industrial buildings
HousingSport facilities
The public sector normally does not invest with a profit motif but rather to
provide "service” buildings, infrastructure and essential community facilities.
Even though the government does not generally compete with the private
sector on a profit basis, there is frequent criticism from the private sector
that the state enters the property market (as well as the commercial and
manufacturing industry) in a way that constitutes competition with the private
sector. This especially applies to the building of houses, industrial complexes,
infrastructure and office accommodation. Amongst other reasons, this is also
one which contributes to the pressure on government to privatise state assets
and businesses in general.
The public sector does not have a central organised body or mouthpiece on
property matters. Management of property takes place in a decentralised
manner at the various levels of government and other public authorities. There
is, however, a statutory Construction Industry Development Board in the
making, which could address this problem in future. In matters concerning
the interests of the private sector, however, a great deal of liaison does take
place between the government (not in its capacity as property owner) and
the South African Property Owners Association (SAPOA).
Financing institutions
Except where the employer is the government or a financial institution, he
usually has to obtain some sort of bond financing to get his project off the
ground.
In the case of residential dwellings and flats the financing is usually provided
by banks, which have the specialised knowledge that is essential for obtaining
and employing the funds, supported by administrative systems, valuers,
inspectors and agencies.
Non-residential housing is financed by banks or by way of participation bonds
that are obtained from finance houses and trust companies.
In all cases where financing is provided for buildings it is in the form of
"mortgage financing" which indicates that a first bond has been registered in
favour of the financier as “mortgagee" by the employer/owner, who is then
the "mortgagor”. If the mortgagor does not meet his payment obligations
towards the mortgagee, the latter can repossess the property and sell it in
execution to recover his loan capital, interest and costs.
The quality of the building is of considerable importance to the mortgagee
as his investment will be better protected by a development of a high standard.
For this reason, mortgagees frequently establish an inspectorate, in the form
of inspectors or clerks of works to ensure that the building work is of a high
quality
As a general guideline one can accept that banks will not provide a loan for
more than 80% on dwelling units, whilst participation bonds and other loans
on non-residential buildings usually do not exceed 66%. These percentages
apply to the value of the building as well as the land and may in exceptional
cases cover professional fees and interim interest.
1.5.2 The building contractor
The contractor can only survive as long as his business is profitable. For this
reason he, and indeed all enterprises in a capitalist economy, attempts to make
a profit.
Unlike the contractor, whose activities are determined by the profit motive, the
professional consultants are remunerated by means of professional fees. This
difference results in different working methods and opinions that can sometimes
lead to conflict.
Colloquially, we often talk of "building firms”, “builders”, "building contractors”,
"contractors”, etc. All these names usually refer to the same commercial economic
entity that should more correctly be called a "building enterprise".
Main contractors and subcontractors in the building industry are normally organised
as line and staff organisational systems as shown in figure 1.8.
The workforce in the building industry (main and subcontractors) usually consists
of the following (appointed by those given in brackets):
(a) Top managementDirectors (by shareholders)
Managing director (by board of directors)
General managers (by board of directors)
Area managers (by board of directors and/or general managers)
Divisional managers (by board of directors and/or general managers)
(b) Middle management (by board of directors and/or general managers)Functional heads of sections
Contract managers
Project managers/site agents
Cost estimators
BUILDING PRACTICE – VOLUME 1
(C) Lower-level management (by board of directors and/or middlemanagement)
General foremen
Foremen
Chargehands
(d) Workforce (by middle and/or lower-level management)
Tradesmen
Apprentices
Operators
Labourers
Manager:
Administration
Manager:
Finance
Manager:
Marketing
Project
manager
Foreman
Chargehand
Artisans/
labourers
Board of directors
Managing director
Manager:
Construction
(production)
Contract
manager
Project
manager
Foreman
Chargehand
Artisans/
labourers
Manager:
Buying
Contract
manager
Project
manager
Foreman
Chargehand
Artisans/
labourers
Legal advisor
Manager:
External relations
Figure 1.8 Line and staff organisation diagram
Manager:
Human resources
Even though it is difficult to single out members of a team on the basis of
importance, it is necessary to point out that the role of the foreman is decisive.
In the hierarchy he is the link between the workforce and the management of the
enterprise, a position that is susceptible to quite a large amount of conflict. His
task is further complicated in that he is generally the person (in the building
contractor's organisation) who has the most frequent contact with the professional
team. He thus stands at the crossroad of channels of information, instructions,
complaints and labour problems. It is also common knowledge that the best
results in terms of production costs and quality can be obtained at the point of
action, that is on the building site. The critical role of the foreman is thus clearly
a determining factor for the success of a project.
Certain attributes which a foreman should possess are the following: Managerial skills (planning,
organising, co-ordination and control)
Leadership
Knowledge of human nature, tactfulness
Must be able to accept responsibility
Must be able to command and also show respect
Integrity
PromptnessObjectivity
The foreman also has to work in a supervisory capacity in respect of colleagues,
from whose ranks he was appointed as direct supervisor.
The responsibility of management to appoint a suitable foreman is thus very
important. In fact, a good appointment will ultimately relieve top management of
part of their work and responsibility.
Characteristics of the building industry
The environment in which the contractor operates and the nature of the
building industry have certain characteristics which complicates his task.
Some of these characteristics are:
Fragmentation of the industry
Cyclical nature of work
Labour supply and training level
Materials supply (price increases beyond the control of the contractor)
Productivity problems
Cost of capital equipment
Lack of operating capital, retention, guarantees, underpayment
Consumer resistance to technological development
Status and image of the building industry
Sources of work
A contractor can obtain building contracts in one of the following ways:
By tendering on invitation or in the open market
By launching a project himself using his own capital
By initiating or participating in the establishment of a syndicate for the
development of a property
By negotiating with a prospective employer for a contract
1.5.3 Subcontractors
By subcontracting the specialist subcontractor enters into a contractual agreement
with the main contractor to do certain work which forms part of the project.
Over the last three decades a strong movement in this direction has taken place
and more and more parts of the project are done by subcontractors, while the
contractor's skilfulness in managing the whole process also increases. In housing
approximately 95% of the work on a house is done by subcontractors whereas in
non-residential building the percentage varies between 40% and 90%.
Specialisation develops out of the known advantages of mass production as well
as from the shortage of "general” trained artisans, leading to the use of
subcontractors.
The following types of subcontractors are operating:
(a) Subcontractors (domestic/ordinary subcontractors)
These are subcontractors who submit tenders to the main contractor and are
appointed by him at his own discretion. Contractually the employer/professional
consultants regard these subcontractors as employees of the main contractor and
they have no direct relationship with the employer. Names of subcontractors are
submitted to the architect for his information and possible objection. The manner
in which subcontractors tender is decided upon by the main contractor and is
usually by means of bills of quantities and/or working drawings.
(6) Nominated subcontractors
These are subcontractors that have to be appointed by the main contractor after
the architect and/or other consultants have nominated such a subcontractor. The
main contractor may lodge a bona fide objection to such a nomination.
Nominated subcontractors do not submit tenders to the main contractor, but like
the main contractor directly to the architect/consultant. As is the case with the
main contractor a number of pre-selected subcontractors may be invited to tender
or tenders may be invited by an open invitation in the press.
Provisional amounts for such specialist work are included in the bills of quantities
and the nominated subcontractors are appointed against these amounts. These
amounts are later adjusted to the final value of the subcontract.
After the main contractor has accepted a nominated subcontractor for a particular
piece of work he is contractually responsible for the subcontractor's work, as in
the case with other subcontractors. In some agreements there is, however,
provision for the main contractor to claim against non-performance of the
nominated subcontractor.
(c) Selected subcontractors
As a result of claims from main contractors if a nominated subcontractor is late in
completing his section of the work a new category namely selected subcontractors
has been introduced.
The basic difference being that a selected subcontractor is not "forced upon the
main contractor. Between the architect/consultant and the main contractor
agreement is reached which subcontractors will be invited to tender. After
acceptance of the tender the selected subcontractor can almost be regarded as
an ordinary subcontractor.
(d) Direct specialist contractors
In exceptional cases the architect or the employer appoints "direct" specialist
contractors who are frequently referred to as "direct subcontractors”. These
appointments are made for highly specialised installations, artwork, etc. where
the main contractor is usually not able to exercise normal supervision and control.
Contractually the main contractor should be informed during the tender stage if
such appointments are envisaged and to what extent he has to provide attendance.
He is also given the opportunity to price for remuneration for such attendance at
the tender stage. No contractual agreement comes into effect between the direct
specialist subcontractors and the main contractor and the employer pays these
subcontractors directly.
(e) General
The main contractor must always ensure that the subcontractors have the
following before he appoints them:
Financial stability
Physical facilities for performing the work
Quality of workmanship
Production capacity
Integrity
Typical problems that are encountered between main contractors and
subcontractors are the following:
Main contractors do not pay promptly
Main contractors do not co-ordinate the work properly
Assistance from the main contractor is insufficient
Subcontractors delay production (working on several sites for various main
contractors where the programmes are continually changing)Untidy workmanship by subcontractors
Finally, it should be mentioned that even though subcontractors usually supply
labour and material they can also (especially in the case of housing) be appointed
for "labour only". In the latter case there are often problems with material wastage
and quality of work.
QUESTIONS FOR SELF-EVALUATION
1. Discuss which aspects you will advise a prospective employer(client) to consider before choosing a
building process for a new
building project.
2.
3.
4.
Why is it important to distinguish between the public and private
sector as employers (clients) in the building industry? Elaborate
on their respective approaches.
What is the role of financial institutions in property development
and which guidelines do they follow when considering financing
different types of new buildings?
(25)
(25)
(25)
Describe the various types of subcontractors which are involved
with building projects and describe in each instance why the various
subcontractors are being made use of by main contractors. (25)
100
REFERENCES
Hauptfleisch, A. C. & Siglé, H. M. 1998. The structure of the building and propertyindustry in South
Africa. Unpublished handbook. Pretoria. (Chapter 1 of this
book has been reprinted here and is hereby acknowledged.)
SOIL MECHANICS AND
BUILDING FOUNDATIONS
CONTENTS
LEARNING OBJECTIVES
2.1
2.1.1
2.1.2
2.2
2.2.1
2.2.2
2.2.3
2.3
2.3.1
2.3.2
2.3.3
2.3.4
2.3.5
2.3.6
2.3.7
2.3.8
2.4
2.4.1
2.4.2
2.4.3
2.4.4
2.4.5
2.5
2.5.1
2.5.2
2.6
INTRODUCTION
Character of soil
Scope and purpose
TYPES OF SOIL AND ROCK
Types of soil
Rock
Resistance of soil
BEARING CAPACITY AND SETTLEMENT
Settlement
Repairs
Recommendations for compact filling under floors and foundations
Selection of filling
Collapse
Sinkholes and subsidence
Swelling clay
Slopes and retaining walls
UNDERGROUND WATER
Groundwater and seepage
Shallow groundwater-tables and swamps
Obstructed drainage on a slope
Artesian fountains and aquifers
Aggressive water
EXCAVATING
Levels
Character of soil
FOUNDATIONS AND FOUNDATION WALLS
QUESTIONS FOR SELF-EVALUATION
2
PAGE
36
36
36
37
37
38
40
41
45
46
47
47
47
48
50
51
53
55
55
55
55
56
57
57
57
58
58
74
35
hain CHAPTER 2
LEARNING OBJECTIVES
The objectives are to introduce the student to the basic principles regarding
soil mechanics and to present various types of foundations which can be used
in the erection of buildings.
After completion of this module the student should be able to distinguish
between different soil conditions and be able to consider alternative foundation
types.
2.1 INTRODUCTION
2.1.1 Character of soil
Before plans are drawn for a structure, the nature of the soil that is to support it
should be determined. If this cannot be ascertained only from existing structures
and test holes, borings should be made. These are often holes from 2 to 3,5 metres
apart, over the entire area, made with an auger about 50 mm in diameter and of
suitable length. As the auger brings up samples of the soil, the character of the
substrata is determined. When the importance of the proposed structure justifies
it, trial pits are dug from 3 to 7 metres apart. It is not safe to rely on the character
of the soil in close proximity to the proposed building site. The actual site has to
be tested. The soils usually encountered in building operations may be classed
under three divisions: rock, natural ground and filling.
Rock, in its original geological formation is spoken of as bed rock. It forms one of
the finest foundations for heavy structures, provided that it is of sufficient area for
the entire building to rest on. It is undesirable to have a portion of the foundation
rest on rock while another portion rests on softer material, since the building will
not settle uniformly and the walls will often crack at the junction of the rock and
softer material. It sometimes happens that the surface of the rock is uneven and
requires blasting and concrete work to secure a good foundation, which adds
considerably to the cost.
Sandstones and limestones are often found in strata (beds or layers) one on top
of another. If these layers are not separated by clay, and the beds are even, they
make a good foundation.
It has been said that "a wise man builds his house on a rock”, which implies that
a foundation should be immovable. Most buildings are however built on a thick
layer of soil with inherent properties that cause problems. Certain problems are
identified before or during construction but others are dormant and may confront
the unsuspecting owner with a catastrophe years later. If a property practitioner
wishes to offer a reliable service, he should be aware of these problems.
2.1.2 Scope and purpose
These lectures present an overview of the specialised knowledge of the
geotechnical civil engineer and the engineering geologist. The purpose is to
make the property practitioner aware of the problems and task of the
geotechnical specialist, who normally has to offer foundation solutions.
Foundations may give way because the strength (resistance) of the soil has been
exceeded, or they may collapse, from millimetres under a portion of the building
to a situation where a whole building disappears down a hole. Clay may expand
or contract, making a building unsafe.
Water in the ground may cause problems and bad stormwater drainage may
convert a downpour of rain into a tragedy in areas where dolomite is found. Water
may contain chemical substances which corrode building materials, and slopes
may be unstable or may move.
2.2 TYPES OF SOIL AND ROCK
When rock weathers, soil is formed. The type of soil is determined by many
factors, of which the most important are the parent rock, the climate and the slope.
Geotechnical maps of the whole Republic and neighbouring territories are
available from the Government Printer. Soil maps for agricultural purposes are
published by the Department of Agriculture and there are engineering soil maps
for most of the larger centres.
A proper soil examination must be carried out for each new development. The
different types of soil that occur are a function of the geology, topography and
climate. In any specific climate condition, soil problems can be predicted from
the geology
The climatic factors to be considered regarding soil types are rainfall, evaporation
and temperature. In South Africa the effect of rainfall is the most important, and
the relevant rainfall figures can be divided into high, medium and low rainfall.
According to Dr HH Weinhart, our climate can be expressed in a single figure
(his N value). Where there is high rainfall, N is less than 2, where there is medium
rainfall, N is between 2 and 5 and where the rainfall is low, N is greater than 5.
As rainfall increases (i. e. there is a decreasing N value), weathering is of such a
nature that more clay is formed, while in a dry climate little clay is formed and the
weathering process is mainly the mechanical breakdown of the rock by changes
in temperature. The final product is then sand and gravel.
From a knowledge of the parent rock and the climate, one can predict which type
of soil problem could be expected. Table 2.1 gives this information. Deep soft
organic layers of clay form in marshes which swell and shrink. Flooding is an
additional problem here.
Table 2.1 Type of problem
Climate
Dry
N greater than 5
Medium
N between 5
and 2
High rainfall
N less than 2
Parent rock
Expected soil type
* All types of rock Silt, sand, gravel
* Lightly colouredSand and clayey
igneous rock and sand
sandstone
* Dark igneousrock and shale
* Lightly colouredigneous rock and
sandstone
• Dark igneousrock and shale
Clay and silt
Sand and clay
Clay and silt
Expected problems
Settlement on loose wind-blown
sand, dune formation, wall cancer
in marshes, erosion, poor garden
soils on slopes
Collapsing sand
Swelling and shrinking, poor
garden soil
Collapsing sand, unstable slopes,
high water-tables (poor drainage)
Deep, soft clay types, unstable
slopes, low bearing capacity and
high water-tables
2.2.1 Types of soil
Soil may be defined as the unconsolidated top layer of the earth. There are
Dbasically four types of soil with individual characteristics: clay, silt, sand and
gravel.
Clay
Clay is soil consisting of particles smaller that 0,002 mm. There are many
different types of clay, but they are all plate-like crystals of aluminium and
silica compounds where the length and width of the plate are 10 to 100 times
the thickness of the plate.
This characteristic determines the properties of clay. The flat fine plates are
like small pieces of paper. They are extremely sensitive to electrochemical
forces and water. Dry clay is as hard as a brick, but when it is wet it can
"flow"-like water.
Water penetrates the adjacent plates and sometimes even the crystals of
the plate itself. The clay then expands when it is wet and contracts when it
dries.
Clay can be recognised by the following characteristics: it is soapy to the
touch when it is wet, it is not shiny and no movement of moisture is visible
when it is rubbed between the fingers.
Silt
The particle size is 0,002 mm to 0,06 mm and it consists mainly of needlelike or sub-rounded crystals,
mainly of silica. The surface effect is less
significant as in the case of clay but silt is still so fine that no individual
particles are visible with the naked eye.
Silt can be easily compacted and structures often settle downwards on it. It
is so impermeable that it cannot be dewatered and it can easily flow away.
It feels like clay, but it does not stick to the hands and can be wiped off. If it
is rubbed in a moist condition, it presents a shiny polished surface and if it
is kneaded in a saturated condition, it becomes alternately dull and shiny as
the surface moisture moves.
Sand
Sand consists of cubic or sub-angular to round crystals of silica from 0,06 to
2 mm in size. In pure form they look like glass but they may be discoloured
by oxides or other salts.
Due to the size and shape of sand, its properties are not greatly affected by
water. The only effect is the fact that moist sand forms vertical walls in a
trench but collapses when it becomes dry or saturated. The permeability of
sand is high.
Sand is easily recognised. It can further be subdivided into fine, medium and
coarse sand, as indicated in table 2.2.
Gravel
Gravel consists of sub-angular to round particles of between 2 mm and 60 mm.
It usually contains quartz, but can contain other minerals in dry climatic
conditions and could even contain gypsum.
Gravel is very permeable, strong and very easy to compact. It can also be
divided into fine, medium and coarse gravel, as indicated in table 2.2.
Table 2.2 Grain size classification
Rock
60
Coarse
2.2.2 Rock
20
Gravel
Medium
6
2
SIZE (mm)
0,6
Sand
Fine Coarse Medium
0,2
Fine
0,06
Silt
0,002
Clay
All particles larger than 60 mm up to the solid crust of the earth are described as
rock. However, rock may be weathered to such and extent that it may be very
similar to soil, or it may be cracked to such an extent that it crumbles to gravel
on exposure.
Rock may be igneous, sedimentary or metamorphic rock. As the name indicates,
igneous rock originated in a fluid form in the deeper layers of the earth and
solidified at or near the surface of the earth. Sedimentary rock is sand and clay
that was transported by water or wind, deposited and changed to rock by
cementation, heat and pressure. Metamorphic rock was also formed in one of
the above ways and then changed by high pressure and heat.
‫܀‬
Igneous rock
Igneous rock originated from lava flow. It is usually finely grained because it
contained air bubbles that were subsequently filled. Sometimes it is intrusive
in the form of plates or passages (as a wall) in the upper older rock and it
then has a coarser crystal structure.
Depending on the percentage of silica and felspar in the rock, it may be light
in colour (felsitic) or dark (mafic). The following is a typical list of rocks that
are light in colour: granite, syenite, felsite and granodiorite. Examples of
dark rocks are: pyroxenite, gabbro, morite, andesite, dolerite and diabase.
Sedimentary rock
When rock weathers, it produces sand and/or clay, which is transported by
water or wind and then deposited. Rapidly moving currents of wind or
water deposit sand while slow-moving currents water deposit clay and
silt. Successive layers of deposited material are compacted and with further
cementation, sandstone is formed from sand, or shale is formed from clay.
Metamorphic rock
The properties of rocks subjected to high pressures, high temperatures and
water, or water rich in chemicals, change to form a new type of rock. In this
way quartzite is formed from sandstone and shale.
When rocks under high pressure and temperature are subjected to large-scale
movements (earthquakes), schists develop. These schists are layered, for
example mica, with a rippled shiny texture.
2.2.3 Resistance of soil
Introduction
Dry sand can run through the fingers like water, but when it is moist, the
same sand will remain firm in a child's sand castle. Buildings can be built
from dried unburned clay bricks, but when the same clay is mixed with
sufficient water it can be pumped.
Strength of soil
The strength of soil is the combination of internal friction and cohesion. These
two concepts can be explained with the help of the braking force of a tyre on
the road as shown in figure 2.1.
Weight
Figure 2.1 Internal friction and cohesion
Tyre
Braking force
Road
The braking force on the wheel will increase if:
(i) The weight of the wheel increases
(ii) The roughness of the road increases
The braking force will decrease significantly if the road is wet. All these factors
contribute to the friction. If the tyre is attached to the road by an adhesive,
there will be a braking force, irrespective of the weight on the wheel. This is
the cohesion part of strength.
Soil
Figure 2.2 The strength of soil
S
Lid
Split box
Table
To determine the actual strength of soil, it is placed in a split box, of which
the lower part is fixed to a table (see figure 2.2). A lid that is just smaller than
the box is placed on it and a mass is placed on the lid, causing force p. To
move the two halves of the box, a force s is required. The results for pure
sand and clay are discussed below.
Pure sand
If there is no force p on the lid, the box will be moved with little effort
(force s), but by increasing p, force s will also have to increase to move
the box. Figure 2.3(a) shows the graph of force versus pressure where
the angle ø is the internal friction angle of the sand. This angle relates
to the angle which the sand forms, as indicated in figure 2.3(b), also
known as the angle of repose.
S
Figure 2.3(a)
Strength versus pressure
Figure 2.3(b)
Friction angle
Beaker
Sand
Clay
If pure clay is placed in the box in figure 2.2, there will be a resistance
s against movement, even if there is no force on the lid. This is the
cohesion of the clay, and it is independent of p, i. e. with increasing
force on the lid, the resistance s does not increase. The strength graph
is shown in figure 2.4.
Cohesion
Figure 2.4 Strength graph for clay
Mixtures of clay and sand
The various soil types usually consist of mixtures of clay and sand and
show the properties of mixtures. The strength graph of such a material
is shown in figure 2.5.
S
Cohesion
Figure 2.5 Strength graph of a sand and clay mixture
Water pressure
As in the case of the car tyre, the effect of water on the strength of soil is of
great importance. In the first place the cohesion is reduced with increasing
moisture, and the effect of force p is also reduced when the water pressure
in the soil increases due to an increase in moisture.
Implications of the above
The strength of sand increases with increasing depth and density. The
strength of clay increases with decreasing moisture content and increasing
density. Increased water pressure reduces the strength of sandy materials
in particular.
Compressibility of soil
Compressibility of soil is the resistance of soil to deformation.
Soil
Figure 2.6 Consolidation test
Steel cover plate
TW
Steel ring
To illustrate this, an experiment such as the one shown in figure 2.6 is
conducted. Soil is placed in a steel ring to keep it from spreading laterally, but
it can be compressed vertically. The experiment is called the consolidation
test and the process is called the consolidation process.
The pressure on the cover plate is increased systematically while the
downward movement of the cover plate is measured very accurately.
With increasing pressure, the cover plate moves down, the soil becomes more
compressed, becomes stronger and offers more resistance to compression.
The graph of pressure versus deflection is shown in figure 2.7.
Downward
movement
Figure 2.7 Pressure versus deflection
2.3 BEARING CAPACITY AND SETTLEMENT
The purpose of a foundation is to transfer the load of the structure to the soil in
such a way that the soil is not exposed to excessive pressure or the structure to
excessive movement that may occur in the soil.
The foundation and soil should not be regarded as separate items but rather as
one item in the complex pattern of interaction between soil and structure. The
structure is equally strongly influenced by the foundation as the condition of the
soil. A flexible structure which is able to withstand some differential movement
will require a lighter foundation than an inflexible, rigid structure that cannot
withstand differential movement.
When the foundation under a building is subjected to pressure, it can stretch or
break. When the load of the foundation exceeds the strength of the subsoil, the
soil fails; this failure is the bearing capacity failure. A safe bearing capacity must
be used; this is usually 1/3 of the failure value.
Even with a safe load the stress on or consolidation of the soil could be so great
that the foundation moves downwards to such an extent that the walls may develop
unsightly cracks, even though the structure is still safe. This process is called
settlement.
Ridge develops
771) =
WIS
Foundation
S
Figure 2.8 Bearing capacity failure
Wall
TRI
Ridge develops
पाया
The result of bearing capacity failure of a foundation is shown in figure 2.8. With
increasing pressure p on the foundation, the soil mass tends to move along the
circle. The foundation moves down while the soil next to the base moves up.
Along the circle the shear strength of the soil opposes the movement. The failure
occurs relatively quickly and causes a ridge to develop next to the foundation (on
one or both sides). It follows that the bearing capacity of a foundation will increase
with increasing depth (under natural ground level) and increasing strength.
This type of failure seldom occurs in practice as the size of the foundations is
prescribed by building regulations. The prescribed sizes are more than adequate
and problems occur only in exceptional cases. In the case of large structures a
structural engineer will be consulted and there should not be any problems.
This type of failure has however occurred on the fine, pure sands of the Cape Flats
where the water table rises to the surface during the rainy season which reduces
the bearing capacity. To prevent this the foundations should be made wider and/or
placed deeper.
Actual bearing capacity failure, usually caused by large-scale movements, destroys
the structure and makes repair impractical.
2.3.1 Settlement
popor
Figure 2.9 Settlement
joppan
Original ground level
Ts
Settlement
When the soil under a foundation is compacted or consolidated due to pressure,
the foundation moves down or settles without failure taking place (figure 2.9). All
foundations settle, except those built on solid rock. The settlement should be kept
within acceptable limits by adhering to the building regulations or by obtaining a
proper design from a structural engineer.
Unacceptable settlement sometimes occurs on pure, loose sand, but in this case
the settlement occurs while the building operations are in progress. At this stage
the building material is still "soft" and the building is only finished off later, therefore
this settlement is seldom of any importance. On soft, saturated clay the settlement
is very slow and cracks may appear over a periodtime.
2.3.2 Repairs
If damage is caused by settlement, the cracks that have developed will stabilise if
there is not a fundamental problem. At this stage repairs can be done by fixing
and redecoration.
Where movement has affected large structures, they can be structurally reinforced
or additionally founded, but this is very expensive.
2.3.3 Recommendations for compact filling under floors andfoundations
Filling is used in most building operations and range from deep terraces, to obtain
a level building site, to shallow fill to provide a level base for a groundfloor surface
bed. In all cases the filling material must be carefully selected and compacted.
The main purpose is to ensure a level surface to place the building on. Occasionally
a fairly deep layer of compacted filling is required to provide a strong base by
which the structural pressure can be distributed to a weak stratum below. This
application must be designed carefully and applied under professional supervision.
The main requirement of filling is that it must be strong enough to carry the applied
pressure without failing and without causing undue movement of the structure.
It must also be stable, i. e. it must not contain expanding substances and there
must be no deterioration with time due to the penetration of water or the presence
of organic material. These objectives will firstly be satisfied by using selected
material and secondly by ensuring adequate compaction when it is placed.
2.3.4 Selection of filling
The ideal is a clean granular soil such as crushed rock, gravel or sand, or a
mixture thereof. Quality material is however not always available at a reasonable
cost.
The correct filling should be specified and compliance enforced by means of
inspection and testing in laboratories and on site. However, the lack of the
necessary testing facilities on the average building site make enforcement difficult.
The following practical guidelines can be given for filling material:
(a) It must be granular.
(b) It must not contain any organic substances such as wood, plants or plastics, as these could possibly
rot and cause cavities or weak areas in the filling.
(c) It must not contain material such as lumps, soft shale or unburned bricksthat may soften when wet.
(d) It should not contain clay since it must be non-plastic for compaction purposes, and clay will shrink
and expand in future with changes in moisture content.
The tendency of clay soil to form lumps is useful in measuring the clay content.
If a handful of moist soil is rolled into a ball and forms a hard lump when it is dry,
the soil is too clayey. If the ball is easily broken by pressing it, the material is
acceptable.
2.3.5 Collapse
Introduction
In this section problems which are not apparent initially, but which can result
in a rapid and dramatic collapse will be discussed. Collapsible soil and
dolomitic areas will be examined.
Collapsible soil
Mechanism
Collapsible soil is loose soil that is held together by a temporary binder,
such as iron oxide or clay.
These soils nearly always have a reddish colour. The grains are packed
in a loose structure, as shown in figure 2.10.
Dry
Binder
Wet
Figure 2.10 Structure of collapsible soil
In a dry condition this soil is strong and can even support multi-storey
buildings. The entire grain structure is supported by the temporary binder.
As soon as the soil becomes wet, the binder softens and the grain
structure collapses under pressure, with an associated sudden collapse
of the soil (it is compacted). Material is not displaced laterally or upward
and no ridge is formed.
Formation
When granite weathers in high rainfall, the result is a mixture of clay
and sand. The clay is leached by the water and a coarse sand with a
very low density and very fine clay as a binder is formed. The clay is
concentrated in the lower layers which are densely compacted.
In a dry climate wind causes sand within dunes to remain in a very loose
condition. Rain, drying out and capillary action bind the sand grains with
iron oxide, which forms a layer of collapsible soil. All reddish sands that
are relatively loose should therefore be regarded with suspicion.
Construction methods
(a) The foundations can be placed deeper than the collapsible soil. Sometimes the collapsible layers are
several metres thick, in whichcase this solution is not economical.
(b) Piles can be driven through the collapsible soil to displace thepressure to deeper levels.
(c) In the case of single storey buildings the foundation trench can bedug deeper, to a depth twice the
width of the foundation, the
excavated material can then be moistened, replaced in thin layers
in the foundation trenches and compacted with a mechanical
compactor.
Repair
(a) In extreme cases of collapsible soil the structure is usually damagedto such an extent that it has to be
rebuilt. If the damage is not too
severe, the foundation can be supported by small pile foundations
and moved by jacks to the desired level. This work must beperformed under the supervision of a
structural engineer.
(b) The problem can be contained by diverting all rainwater into concretechannels and ensuring that no
leaking water or sewerage pipes exist.
2.3.6 Sinkholes and subsidence
Origin
Dolomite is limy rock that originated from chemical deposits in shallow seas.
It occurs in extensive areas of South Africa and in certain centres it is not
always possible to avoid these areas.
When carbon dioxide dissolves in water it forms a weak acid that in turn
dissolves the calcium in the dolomite and carries it away, leaving only a chert
portion. Very large cavities are formed; the Cango caves are an example
of this. If there is a soil layer above the dolomite, a real trap is formed - as
shown in figure 2.11. If water regularly flows downward, the soil bridge is
eroded from underneath until it collapses and a sinkhole is formed.
Sometimes the underground cavities are filled with chert gravel and the
topsoil may flow into this. In such a case only a subsidence is formed at
the surface.
Sometimes the cavities are filled with wad (a very fine silt) that has no strength
in a saturated condition. When the water table becomes lower, the wad flows
to deeper cavities, even through the smallest passages, and bigger voids, as
shown in figure 2.11, develops.
Soil
Soil
bridge
Cavity
Figure 2.11 Formation of a sinkhole
Soil
Dolomite
The most dramatic example of the above in South Africa occurred in the
Carletonville area approximately thirty years ago. There an entire stone
crusher, as well as house, with all its occupants, disappeared down a
huge sinkhole.
The probability that sinkholes will occur is reduced in relation to:
(a) the thickness of the soil layer above the dolomite;
(b) the presence of intrusions in the form of supporting plates.
Prevention
(a) The simplest solution is to avoid dolomite areas. All such areas shouldbe viewed with suspicion.
(b) (i) If there is no alternative, specific areas in dolomite regions must bescientifically identified where
the possibility of sinkholes is minimal.
These areas are usually identified through extensive drilling and
sonar testing in order to map those areas which can be used for
development. Geological maps are available in metropolitan areas,
indicating the extent of underground cavities. Consult a geologistin this regard.
(ii) The foundations of the building must be adapted to the situation byspreading the structural weight
over a larger than usual area.
(c) With existing structures on dolomite, no water must be concentrated atany point. Rainwater must be
drained off as far as possible in watertight
concrete channels or PVC pipes. Great care must be taken that
sewerage and water pipes do not leak.
2.3.7 Swelling clay
Introduction
In the medium-rainfall areas clay soil always involves risk because it may
swell. Most developed areas in South Africa has some clay soil. A large
number of buildings are cracked to such an extent that they are unsafe, and
millions of rands are spent annually on fixing cracks resulting from swelling
clay.
Mechanism
Clay is a plate-like mineral but the finest and flattest platelets occur in the
case of montmorillonite clays. Water molecules penetrate between the layers
and cause the mineral to expand considerably, as shown in figure 2.12.
These clays originate from the weathering of darkly coloured igneous rock,
or where certain types of shale weather to become clay in medium-rainfall
areas.
Montmorillonite clay
000
OOOO
Figure 2.12 Swelling clay
Plates
Molecules
Variation in moisture conditions
Where there is a deep water-table in medium-rainfall areas the water moves
up and evaporates, with the result that lime forms in the upper layers when
the clay dries out. During winter and between rainstorms cracks develop in
the soil, which could be several metres deep.
When a building is erected on this clay, evaporation is cut off and the cooler
area under the house attracts moisture. The moisture content of the clay
increases, the clay swells, the building is lifted unevenly and the walls crack.
When development of a township takes place in a wetland area, the drainage
improves and large trees are planted which absorb the moisture, the clay
shrinks and the buildings crack.
Requirements for a swelling or shrinking problem
The following must exist for a swelling or shrinking problem to develop:
(a) There must be a deep active layer of clay present.
(b) The layer of clay must be desiccated (dry) or totally saturated.
(c) There must be a mechanism that will change the moisture conditionsappreciably.
Prevention
(a) If possible, areas with deep swelling clay must be avoided.
(b) If the layers of swelling clay are less than 2 m thick, the clay can beremoved and replaced by inactive
gravel.
(c) The structure can be erected on a reinforced concrete raft foundation sothat it can withstand
movement without cracking.
(d) The structure can be provided with joints to ensure that movement takesplace at controlled
positions.
(e) Piles can be driven through the active clay and the structure placed ontop of the piles, completely
clear of the soil.
(1) Great care must be taken that sewerage and water pipes do not leak. Standard flexible systems are
available.
(g) Concrete paving can be built around the entire building to move theabrupt transition between
covered and uncovered areas further awayfrom the structure.
(h) If there are existing buildings in the area, they could be examined forcracks and repairs. This will
show up any swelling problems.
(i) Consult an expert geotechnologist when clay is encountered.
2.3.8 Slopes and retaining walls
Introduction
Nature tends to maintain areas as level as possible. Therefore, to create a
difference in height between level plains, there must be a resisting force.
To accommodate a difference in height, one needs an intermediate slope or
retaining wall. Rock can stand vertically but clay, sand and silt require very
gentle slopes.
Failure of slopes
Simple slope
Figure 2.13 Circular shear failure
TWITT
TIIVIT
UUTTT
Circular failure
A slope can fail in different ways, the most frequent shown in figure 2.13. In
this case the slope fails along a circular failure level.
The force causing this movement is the weight of the soil above the internal
friction angle. This force will increase with steeper slopes and heavier soils.
The force that resists the movement is the shearing strength of the soil along
the failure circle.
BUILDING PRACTICE – VOLUME 1
Effect of water
Increased moisture necessarily makes a slope less safe. It reduces the
strength of the soil and increases the weight of the soil, facilitating a slide
down. Water can also increase the pressure on the failure level, which will
reduce the strength of the slope even further.
Prevention of failure
(a) Existing slopes should not be made steeper and no new slopes shouldbe built without consulting a
civil engineer. Construction work with slopesis a specialised field.
(b) If a building is to be built on a steep slope or above a steep slope, anexpert should also be consulted.
(c) Keep water away from the slopes by using planned channelling.
(d) Plant large trees with tap roots on the slopes. They absorb water fromthe slopes and bind the soil
mechanically.
Retaining walls
Retaining
wall
Drainage
hole
Figure 2.14 Retaining walls
Drainage channel
-Original slope
-Filling
Stone filling
If there is not sufficient space to place a slope between two levels, a retaining
wall must be used. This retaining wall is a structure of concrete, brick or even
stones in wire baskets. The strength of the soil is again of importance, and
the dimensions, shape and weight of the retaining wall are to be designed to
accommodate the particular situation.
One of the critical aspects is to prevent water pressure from adding to the
soil pressure building up behind the wall. Drainage holes must be made in
the wall at regular intervals (+1,5 m) and a drainage channel should be
provided behind the wall.
2.4 UNDERGROUND WATER
2.4.1 Groundwater and seepage
Groundwater causes foundation problems. At a certain depth in the ground the
groundwater table is found, which is the level of the free water in the ground of
that area. The depth of the groundwater table at any particular place at any time
depends on a number of factors.
Those factors include the depth and nature of the soil, the geology and topography
of the terrain, rainfall, vegetation and evaporation. Sometimes the groundwater
level is above natural ground level as in the case of fountains, streams and marshes.
In other areas it can be dozens of metres below the surface or virtually non-existent.
Groundwater is not static, as there is a continuous flow of water in the ground,
causing a rise and fall in the table level.
A great deal of the rain that falls on a slope of a hill will seep through the soil to
the rocks below and then along the surface of the rocks to the valley. This flow
can occur as a continuous expanse of water across the whole slope of the hill or
it can be restricted to certain channels or underground valleys formed by rock.
When these channels are obstructed or blocked, the water rises to the surface
as a fountain.
Seepage problems are encountered when buildings are constructed below the
groundwater table or when water flow is obstructed.
2.4.2 Shallow groundwater-tables and swamps
In South Africa one should be careful when building on low-lying ground. In the
dry season the soil may appear perfectly safe for building and the groundwater
may be at a depth of one to two metres, but in the rainy season the soil may be
waterlogged up to the natural ground level.
One should be cautious about building in areas with heavy black soil and reedlike vegetation. The only
way such an area can be made suitable for building is
to divert the water flowing into it by water channels above ground and subsoil
drainage systems below ground. The drainage trenches divert water away from
the area while a network of agriculture subsoil drains is built to drain the excess
water in the ground away and maintain the groundwater level at an acceptable
depth.
2.4.3 Obstructed drainage on a slope
Moisture problems are frequently encountered when buildings are built on slopes,
especially in the case of structures on two or more levels. In this case building
operations during the dry season may not reveal the problem.
.
Floor level
Soil
Rock
Flow of moisture
Obstruction
Figure 2.15 Drainage on a slope obstructed by a building
When a building is placed on a sloping site, rainwater seeps through the higher
lying ground and flows along the surface of subsoil rock or other dense soil until
it dams up against the building and causes dampness and even free water inside
the building.
If this problem is anticipated, damp proofing or tank proofing can be applied to
the outside surface of the wall (or between "skins” of the wall). Water will still
dam up and exert pressure against the wall which requires that a agriculture drain
be constructed between the wall and the higher lying ground to catch the seepage
water, which should then be channelled around or under the building.
The only real solution for serious seepage in existing buildings is that the outside
wall is regarded as a basement retaining wall and it is provided with seepage
holes for water to drain through. This water is then collected in a floor drain and
pumped away. An inside wall is built as a decorative wall to form a cavity with
the floor drain located in the bottom of the cavity. Several drains can be provided
along the upstream sides of the building in order to drain the higher lying ground
in general.
2.4.4 Artesian fountains and aquifers
An aquifer is a relatively porous geological stratum of loose stone that can store
water. If this layer occurs between two layers of less porous rock, such as shale,
the aquifer becomes an underground dam. If the aquifer lies on a slope, it will
become filled with water during rain and the lower end will be subjected to
considerable hydrostatic pressure. If a hole is drilled into the aquifer at this point,
the water will flow out at the surface because of the artesian condition (the water
is under pressure).
In cases where there is a crack or opening in the top layer over the aquifer, an
artesian well can develop below the building which has been unknowingly
constructed over such a crack (see figure 2.16), resulting in a natural outflow of
water inside the building whenever the water table rises.
Building
Artesian
well
Crack or fissure under
water pressure
R
Porous
aquifer
Impenetrable
layers
Figure 2.16 Artesian fountain
Impenetrable
layers
Water
table
This problem can be solved by the installation of a sump and pump with automatic
water depth control.
2.4.5 Aggressive water
In conclusion it should be mentioned that the groundwater could contain chemicals
that may be dangerous to building materials.
Dissolved sulphates and other salts are transported by water and absorbed by
foundation walls. When crystallisation takes place, the crystallisation forces may
cause structural damage. The presence of certain caustic agents accelerates the
corrosion of metals. Water containing sulphates are present in certain areas of
South Africa and requires specialised knowledge and expert analysis and advice.
2.5 EXCAVATING
2.5.1 Levels
When a site is prepared for the erection of a building, it is done in such a way
that the structure will be placed on a specific level. All the work is executed in
relation to this specific level, also known as a datum line, or simply the datum.
On the plans levels are given in metres above and below this line for all the floor
levels and other building components.
BUILDING PRACTICE – VOLUME 1
In the case of all buildings the datum is established from contour maps of the
site.
2.5.2 Character of soil
Before plans are drawn for a structure, the nature of the soil that is to support it
should be determined. If this cannot be ascertained from existing structures,
test holes or borings should be made. These are done to a grid pattern over the
entire area, made with an auger about 50 mm in diameter and of suitable length,
or by digging holes for personal inspection.
It is generally safe to build on bed rock provided that the foundation beds are kept
level. Gravel, even when mixed with small boulders, can be considered perfectly
reliable for any ordinary structure, under normal conditions.
Sand will carry very heavy loads, if it is confined. Great precautions must be
taken to confine it properly, and also to keep water from it, especially running
water, as the action of this can wash it away underneath foundations. ·
When compact and dry, clay will carry large loads, but water should be kept from
it, both under and around the structure as the foundations might fail, owing to the
pasty or semi-liquid nature of wet clay. Clay containing moisture could be suitable
as a foundation, provided that the water contained in it is retained. Fluctuations
in water content will cause swelling and shrinking resulting in structural damage.
Serious failures in buildings can result from founding on sand or clay, and where
it cannot be controlled, clay and sand as a base should be avoided.
Marshy spoils and filling should only be built on when using raft foundations or
piling, designed and supervised by a structural engineer.
2.6 FOUNDATIONS AND FOUNDATION WALLS
Purpose and design
Purpose
The purpose of a foundation is to provide a level surface to work on
and to enable the dead and live loads acting on a structure to be safely
transferred to the ground without causing excessive settlement which
could damage the structure or adjoining structures. To enable foundations
to perform this purpose, they must be placed deep enough to ensure
stable conditions, and to avoid damage being caused by surface water.
Foundation design
Foundation design can be divided into three main stages: The determination of the safe bearing capacity
of the soil on which
the foundation is to be constructed.
The selection of the type, size and depth of the foundation to be
used to ensure that the safe bearing capacity of the soil is not
exceeded, and that excessive settlement, particularly differential
settlement, is avoided.
The structural design of the selected foundation type must ensure
that it is capable of carrying, without disintegration, stresses to which
it is to be subjected.
Types of foundations
Strip foundations (unreinforced)
Unreinforced strip foundations are used for load-bearing walls for small
buildings such as houses. The foundation, shown in figure 2.17, usually
projects equally on either side of the wall and is made of concrete having
a mix of not less than 1:3:6 (cement: sand: stone, by volume). The
thickness of the foundation (E) must be at least equal to the projection
of the foundation (D) and never less than 150 mm.
The width of the foundation would be established by calculating the load
(including weight of the foundation) to be distributed per square metre
of soil, having allowed for a safety factor and according to the bearing
capacity of the soil. For simple structures it is unnecessary to calculate
the required foundation because the National Building Regulations can
be followed with safety.
The allowable bearing pressure would be established either by loading
tests or by establishing the type of soil. Note that the damp-proof
course (C) in figure 2.17 must be at least two layers above ground level
to prevent seepage from the outside at or above the damp-proof course
level.
Min. 2 brick courses
Min. 500 mm
B
A Solid one brick wall in superstructurein 1:5 cement mortar
B Solid one brick wall in foundationsin 1:4 cement mortar
C Damp proof course (DPC)
E
Figure 2.17 Strip foundation with solid one brick walland solid floor
Strip foundations on sloping sites
On sloping sites it is usual to step the foundation to follow the gradient
(slope) of the site and at the same time to keep the foundation the
required depth below the ground, as shown in figure 2.18 - see method
1 and method 2. Dimension (B) has to be at least 300 mm. Down step
(C) must be done in heights in any plural of the brick thickness plus the
bed joint thickness (in brick layers).
C = Downstep in heights of brick courses(in plurals of a brick course + bed joint)
‫ܛܛ‬
B
Natural ground
level (NĞL)
Min. overlap 300
Strip
foundation
METHOD 1LONGITUDE SECTION THROUGH STEPPING STRIP FOUNDATION
Reduced ground level
Original natural ground level (NGL)
Strip
foundation
X = Natural angle ofrepose of ground
A
*Min. 300
Consolidated ground
filling
METHOD 2LONGITUDE SECTION THROUGH STRIP FOUNDATION ON
UNDISTURBED AND CONSOLIDATED GROUND
Figure 2.18 Strip foundation on sloping sites
Deep strip
The deep strip foundation, shown in figure 2.19 is particularly useful in
firm shrinkable clay, where the depth of the foundation (A) is likely to be
approximately 1,2 metres and the width (B) is likely to be 380 mm which
is adequate for a two-storey building in this type of ground. The deep
strip foundation eliminates the need for brickwork below the ground. The
damp-proof course (C) must be at least two layers above ground level.
It is advisable that this kind of foundation is designed by a structural
engineer.
Trench excavated
wider than
foundation to
provide working
space
NNNN
B
NON
Figure 2.19 Deep strip foundation
C = Damp proofcourse (DPC)
Min. 2 brick courses
Foundation sides
formed by
shuttering
A
Wide strip
The wide strip foundation, shown in figure 2.20, is used to give a greater
area of foundation in contact with the soil where the bearing capacity of
the soil is low.
Owing to the excessive width (A) and therefore thickness, it is usual to
place reinforcement (B) in this type of foundation, which allows the mass
distribution to be over a wider/greater area. It is good practice to place
concrete blinding (C) on the exposed bottom of the trench to prevent the
soil from being disturbed by workmen and to prevent the reinforcement
from becoming contaminated by the soil. The damp-proof course must
be at least two brick courses (D) above natural ground level.
DPC
Min. 2 brick courses
KA
+
280
330
800-1000
A
230
Figure 2.20 Wide strip foundation with solid 1 brick cavitywall, solid floor and 11/2 brick foundation wall
Raft foundations
The raft foundation, shown in figures 2.21, 2.22, 2.23 and 2.24, is used
for building on filling, soft natural ground and in areas which are prone
to ground movements caused by clay. The particular advantage of a
raft foundation over a strip foundation is that it acts as one unit, and
differential settlement of the foundation is eliminated. This type of
foundation takes the form of a slab of reinforced concrete, often with
concrete ribs underneath. The size of the raft could be the entire size
of the building it carries, or multiple rafts with expansion joints can be
used. The ground under the edge of the raft must be protected from
deterioration through weather conditions. This can be achieved in a
number of ways: by laying 1 m wide, 75 mm thick paving around the building, as
shown in figure 2.23;
by deepening the edge beam (A) as shown in figure 2.23;
by installing a well maintained agriculture drain (A) encased in gradedfill (B) alongside the edge of the
raft, as shown in figure 2.24.
In figure 2.21, 2.22, 2.23 and 2.24, all the unsuitable soil under the
proposed raft is removed and replaced by hard-core filling which is
blinded (surface area covered) with either sand or weak concrete ready
to receive the reinforced concrete raft. In all cases the damp-proof course
must be at least two brick courses above the ground level.
C
0111
110,
3440
2780
OLL" OLL
110
110.
DPC
|110
110
Slab 150 mm thick
6240
5580
PLAN
Slab 150 mm thick
वन
ARTY
SECTION C-C
Figure 2.21 Raft foundations
110
110
***-110
110
DPC
150
DPC
+1104
Internal wall
Thickening in slab
to form wall
foundation
Stool to support
reinforcing
600
*
*
t
220
220
#
t
600
Exterior wall
DPC
Ground back filling
Figure 2.22 Typical detail of raft foundation toe
INGL
А
DPC min. 2 brick courses above NGL
Concrete paving strip
1 000
Edge beam can be deeper
t
Figure 2.23 Raft foundation with projection to receivebrickwork
75
DPC min. 2 brick courses above NGL
B graded fill
Perforated drainpipe
Figure 2.24 Raft foundation with drainage protection
Isolated pad foundations
Isolated pad foundations are used for columns or detached brick piers as
shown in figure 2.25. The area of this type of foundation is determined
by calculating the dead weight of both the column (A), foundation (B)
and load to be carried, and the safe bearing capacity of the soil. The
thickness of the foundation (C) must be at least equal to the projection
from the column (D). Any necessary reinforcement is placed in the
foundation.
Pad foundation
thickness C
X
V/
T
TU
>
CH
el
H
27
Figure 2.25 Isolated pad foundations
Pier and beam foundation
ColumnA
Column pad
foundationB
Steel reinforcingE
Pier and beam foundations, shown in figure 2.26 are used for light
buildings such as houses, low-rise offices and factories on swelling clay,
or through shallow layers of poorly compacted filling to a firmer foundation
soil.
In this system, short unreinforced concrete piles (A) are cast in auger
bored holes. The piles, which are usually placed at pre-designed centres,
are spanned by reinforced concrete beams (B), which in turn carry the
walls of the building. (C) is the damp proof course.
It is possible to vary the diameter of the pile and bore depth, depending
on the specific soil conditions.
Short bored piles are often not reinforced, but if the beams are to be cast
some time after the piles, mild steel reinforcing (D) should be pushed
into the top of the pile and bent into the body of the beam later.
The beam (B) should be cast on top of a 75 mm layer of ash, sand or
other compressible material to enable the clay to expand and contract
without affecting the beam above.
69
Series CHAPTER 2
BUILDING PRACTICE – VOLUME 1
The beams can also be kept 50-75 mm above the excavated trench
floor and sealed off with a lining as shown (E).
Slab loose from wall
Steel reinforcing D
Compressible
material
NNNNNN
NNNNNN
Figure 2.26 Pier and beam foundation
Beam B
Lining to keep free
space under beam
free from filling E
Pile A
Foundations for high-rise buildings
Although there are quite a number of different types of foundations, most
are applicable to particular situations, and there is rarely any choice once all
the parameters are known. The two main types of foundations for high-rise
buildings are pad foundations and piled foundations.
Before going on to site, it is first necessary to be quite clear as to what the
soil conditions are. The services of a geotechnical engineer is normally
obtained. Through sampling and laboratory tests he will determine the
bearing capacity of the soil and hence determine on what level the foundations
can be laid.
Pad foundations
The dimensions of a pad foundation are determined by various factors,
such as the load imposed on the pad and the soil conditions of that
specific area. In figure 2.27 a typical framed concrete structure supported
by columns and pad foundations is shown.
Flat slab
(flat
underside)
Pad
foundations
Ribbed slab
(with beams
to underside)
Pad
foundations
Basement
XXXXXXXX
Column
Part longitudinal section Part transverse sectionFLAT SLAB CONSTRUCTION
Column
Basement
Part longitudinal section
Part transverse section
RIBBED SLAB CONSTRUCTION
Figure 2.27 Pad foundations
Piled foundations
A pile is a structural member, wholly or partially buried in the ground,
which receives load at its upper end, and transmits that load at depth to
the substrata.
Piles transfer loads from buildings and civil engineering structures to the
supporting soil; they can be more effective than foundations formed
nearer the ground surface in a wide range of situations. They are
particularly appropriate where soft or loose soils overlay strong soils or
rocks at depths that can be reached by driving or boring. Piling methods
are adopted when: The load imposed by a structure cannot be spread sufficiently over
the available ground area without exceeding the allowable bearing
capacity of the soil.
No firm bearing strata exists at a reasonable depth and the applied
loading is uneven (often making the use of a raft inadvisable).
Such firm strata does exist, but at a depth that makes slab, strip, or
column base founding uneconomical.
Shrinking clay is present, and piling serves as a means of founding
below the zone of seasonal moisture movement.
Pumping of subsoil water would be too costly, or planking and
strutting to excavations would be too difficult to permit the use of
column base foundations.
Structure is to be constructed over water.
Tension forces result in uplift or overturn, due to windforce, and there
is thus a need to resist such turning and uplift.
Resistance to lateral loads is necessary, in which case a raft would
be unsuitable.
Underpinning or strengthening of existing foundations is necessary.
Types of piles
Before a design engineer can consider what type of pile is best suited
to a project, the following basic information is required: Detailed soil information
A column layout with column loads
Allowable total and differential settlementsKnowledge of the site and its environs.
A wide range of piles can be used of which some are provided by
specific piling contractors only. Driven, pre-formed piles consist mainly of
precast concrete piles, steel H-piles and timber piles. Bored cast-in-situ
piles are normally augered and filled with concrete with the necessary
steel reinforcing. In figure 2.28 the complete sequence of such a pile is
shown.
Drilling
Enlarging
of base
Hand cleaning
of base
Concreting Completedpile
Ground
water level
- Ground
- Silt/clay
Sandy gravel
Stiff fissured clay
Rock
Figure 2.28 Stages in construction of large-diameteraugered foundations with reamed-out bases
QUESTIONS FOR SELF-EVALUATION
1. Why is it important to consider geotechnical problems in thebuilding industry?
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
List the various typical types of soil and give a short description
of the properties of each.
Explain what is meant by the "strength” and “compressibility” of
soil.
How can the problems caused by swelling clay in an existing
building be solved?
What is the difference between settlement and failure of a
structure?
Explain the causes of two types of soil/structural collapse.
What recommendations should be followed for soil filling under
floors and foundations?
What problems are caused by groundwater and which solutions
are available?
Discuss the laying of foundations on sloping sites. Make ample
use of sketches to support the discussion.
Provide a sketch with descriptions of a raft foundation.
Sketch and discuss an isolated pad foundation.
Discuss when a pier and beam foundation will be used.
(20)
(20)
(20)
(20)
CONTENTS
LEARNING OBJECTIVES
3.1
3.1.1
3.1.2
3.1.3
3.1.4
3.1.5
3.1.5
3.1.7
3.2
3.2.1
3.2.2
3.3
3.4
3.4.1
3.4.2
3.4.3
3.4.4
3.4.5
3.4.6
3.4.7
3.4.8
3.5
3.5.1
3.5.2
3.5.3
3.6
MASONRY WORK
Introduction
Joints in masonry
Bonding
Reinforced brickwork
Lintels
Brick arches
Cavity walls
DAVIP-PROOF COURSES
Horizontal damp-proof course
Vertical damp-proof course
FIREPLACES AND FLUES
ROOFS
îypes of roofs
The design of trusses
Joints between members of irusses
Bracing and fixing of roof structure and coinponents
Hipped roots
Valleys
Gutters
Roof coverings for psiched roofs
CONCRETE, REINFORCING AND FORMWORK
Concrete
Reinforcing
Formwork
BASEMENTS
QUESTIONS FOR SELF-EVALUATION
3
PAGE
76
76
76
76
78
83
84
87
88
89
90
93
93
95
95
101
102
105
107
108
109
111
123
123
127
133
141
LEARNING OBJECTIVES
The objectives are to iniroduce the student to basic building construction
methods and how it is applied in practice.
After completion of ihis module the student should be able to administer the
execution of basic building construction work.
3.1 MASONRY WORK
3.1.1 Introduction
Simple siructures are mainly constructed by masonry work where the primary
function of a wali is io enclose or divide space. In addition it may have to provide
support. Wal! s nay thus be divided inio two types: load-bearing and non-loadbearing. In order to fulfil
these functions efficiently, there are certain requirements
which it must satisfy, namely the provision of adequate:
strength and stability
weather resistance
durability
fire resistance
thermal insulation
sound insulation
A masonry wall is built of individual blocks of material such as bricks, concrete
blocks or sione, usually in horizontal courses, cemented together with moriar.
3.1.2 Joints in masonry
Meaning of masonry
By the term masonry is not meant only ihe bricks, blocks or stone, but also
the mostar in the joints. Its sirength is dependent on the strength of the blocks,
the sirength of the mortar and the method of layirg and bonding. Therefore,
the value oí a good masonry, so far as strength is concemeci, may be
decreased by the use of inferior mortar or by being laid by a tradesman who
is not proficieni in the trade. Mortar for ordinary masonry is mixed 1:6,
cement: sand by voluine.
Brickwork, being the most commonly used in masoniy, will be inainly ceait
with in this part of the coursework as the principles involved are applicable
to all masonry
O
Size of mortar joints and bricks
Thick joints in face brickwork preseni an unsightly appearance. In laying
bricks, a layer of mortar is first spread over the preceding course; then, each
brick is iaid in place and tapped with a bricklayer's trowel until sufficient moriar
is squeezed out to make a solid joint of the required thickness.
To force a brick down until it touches the brick beneath is not good practice,
as the joints become so thin that they lose much of their strength. The more
regular the surface of the bricks, the closer they can be laid and ihe smaller
the joints will be. With ordinary masonry, ihe joints should average 10 mm
in thickness for maximum wall strength.
The size of standard clay bricks is 222 x 105 x 73 mm with small tolerances
being allowed in each diinension. See figure 3. i.
| 131
222
106
Traditional brick
Header face(B)
Plaster brick
Frog
(A)
Press brick
Arris edges(D)
Stretcher face(C)
Figure 3.1 Standard bricks
190
90
Modular brick
UTIE
Hollow block
Wire cut brick
77
CHAPTERS
Jointing
Jointing refers to ihe finishing process regarding the exposed inortar between
the masonry. Pointing is used in the same sense in practice. Figure 3.2
shows various names of jointing commonly used. (A) shows struck or weather
jointing, and (3) shows a recessed joint. The latter (B) has poor weathering
qualities as water can gather at the bottom of the joint and, if this freezes, the
brickwork and mortar at this point will deteriorate. The jointing markedi (A) is
recommended for general use as its weathering ability is superior to (B) on
suríaces exposed to the elements.
A Struck joint
Recessed joint
Figure 3.2 Joints in brickwork
Wall joint
Cross joint
Closer
Vertical joint
Perpend line
Bed joint
3.1.3 Bonding
By bonding brickwork (or blockwork) is meani the process of laying bricks across
one another so that one brick will rest on parts of iwo or three bricks below it which
implies thai brickwork should never have a continuous vertical joini extending over
more than one layer of brickwork. This amounts io the same thing as breaking
ihe joinis. It is difficult for a wall built in this manner to crack except through actual
breaking of ihe bricks. When the bricks are placed length-wise on the face of the
wall, as at figure 3.3, they are termed stretchers. When placed crosswise, with
their ends exposed to view on the face of the wall, they are known as headers.
À course is a co. npleie layer of bricks on its bec joint, running the lengti of the
wall. When the course consisis of streichers it is called a stretcher course, and
a header course consisis of brick heads showing on the face of the wall.
When bricks are laid on their ecge and with their heads exposed io view, a brickon-edge or roller course
is formed. A course laid with the bricks standing on its
edge is called a brick-on-end or soldier course. By lap is meant the horizontal
disiance between the vertical joints in two successive courses with ihe minimum
required one quarter of a brick length.
When a wall is buiti consisting of one "skin" only it is known as a half-brick wall,
whilsi a two "skin" wall is known as a one-brick wall.
D
Figure 3.3 Brick courses
Stretcher course
Header course
Brick-on-edge
course
Soldier course
Typical brickwork bonding principles are shown in figure 3.4.
mes
tel.
Figure 3.4. Brickwork bonding
Header bond
General rules for bonding:
The arrangement of alternate courses is usually identical. (There are
exceptions to this rule, as in garden-wall bonds.)
There should be no continuous vertical joints on the face of a wall.
In stretcher bond, the bricks overlap each other by half a brick. In most other
bonds, they overlap a quarter of a brick.
Closers should only be used near the comer of a wall.
Walls should show the same appearance on boſh faces of the wall, e. g. a
course consisting of stretchers on the front elevation should show stretcher's
on the back elevation.
As few closer's as possible should be used.
The following cominonly-used brick bonds are available:
Header bond (figure 3.5)
When all ihe courses present the ends of the bricks on the face of the wall,
the wall is then composed entirely of headers, and is said to be built in header
bond. This method is particularly suitable for use in sharp-curved walls.
HUNIA
Figure 3.5 Header bond
Stretcher bond (figura 3.6)
All the courses consist of stretchers with two hali-brick leaves and is the
mosi commonly used bond. The wall is also used for internal walls where
the wall is halí a brick thick.
Figure 3.6 Stretcher bond
VanMNULU HINDI
English bond (figure 3.7)
In English bond, probably the strongest method of bonding brickwork,
header and stretcher courses are laici alternately, making use of closers
near corners.
Figure 3.7 English bond
English cross bond and Flemish bond (figuros 3.8 and 3.9)
These bonds are altemalives io üle English bond and also provides a stronger
wali than strelcher and header bond wails.
Figure 3.8 English cross bond
Figure 3.9 Flemish bond
Toathing
Toothing is used where ii is known that extensions are io be added to a wali
at some later daie. The end of the wall is left, as shown in figure 3.10, so thai
the additional work can be carried out without disturbing the existing wall.
Toothing
Figure 3.10 Toothing of brickwork
Toothing
Reking
Raking is the ierm used where brickwork is steppeci down to ensure proper
bonding at a later cate when work is resuined. This is superior to foothing.
See figure 3.11.
Figure 3.11 Raking of brickwork
Raking
(Steps)
3.1.4 Reinforced brickwork
Reinforced brickwork consists of brickwork boncied in the normal manner, but
with metal reinforcernert (commercially known as “brickforce") incorporated in
the joints. The reinforcement stiffens the wall generally and adds to the tensile
strength of the wall by functioning in the same way as reinforcing in concreie work.
Ordinary mild steel reinforcing up to 10 mm in diameter is also used in joints where
more sirength than that afforded by "brickforce" is required.
Reinforced brickwork can be used io resist unequal settlemeni when structures
are built on soils of unequal bearing capacity and should be used under the eaves
io distribute roof loads more evenly, and over windows and doors to prevent
cracking. Brickforce consists of two wire strands spaced 100 mm (half-brick walls)
or 200 mm (one-brick walls) apart, joined by cross pieces at 150 inm to form a
ladder effect. It is supplied in rolls or long lengths laid flat. Brickforce laid in the
horizontal joints oi brickwork over an opening act as a beam. Tihe amount of
reinforcement necessary is determined by the span. For example, for a typical
window or door opening 1 200 min wide, iwo courses of reinforcement would be
necessary and the height of the brickwork above the opening would have to be
at least 5 layers. li is good practice to place brickforce in every fourth layer of
brickwork in ail instances as ii substantially enhances the stability and strength
of a wall. Figure 3.12 shows reinforced brick inasonry.
Figure 3.12 Reinforced brick masonry
3.1.5 Lintels
Reinforcing in
stretcher brick joints
Header brick course
over opening
Lintels are the "beams” formed or placed over openings in brickwork.
In situ brick lintels
in situ lintes are createci by forming a "beam” in the brickwork by reinforcing
it wiih sieel, usually brickforce. In general the reinforcement is placed in the
first moriar bedding joint above the soffit (bottom row) bricks over the opening.
The amount of inforcement required cepends on the size of the opening,
the depth of the lintel section and the loads to be supported. It also depends
on the position of the opening in the wall and on the proximity of adjacent
openings to each other. These factors will also determine how many layers of
brickwork reinforcing is required.
Special care shoulc be taken to ensure complete filling of all joints with mortai
and full embedding of the reinforcement in the mortar. The inortar in all joints
must be solid. Sicie cover of reinforcement should not be less than 10 min
io prevent listing. See figure 3.13.
ELEVATION
х
Х
HHH
SECTION X-X
Steel reinforcing
bedded solid in
mortar with at
least 10 mm
cover to outside
of wall
Figure 3.13 In situ brick lintels ("built-in-position")
In situ reinforced concrete lintels
In situ concrete lintels are reinforced with steel bars to give them tension
strength. These lintels are usually designed for specific applications, wnicy
will determine the steel reinforcing and concrete inix strength required. Typical
examples are shown in figure 3.14. (A) to (C).
Rooftie
Beamfilling
Sprocket
Gutter
Fascia
board
Gutter
Steel
reinforcement
Roofing
Roof batten
Wall plate
V-joint in plaster
Stirrups
Lintel depth
Reinforced concrete lintel
(precast or cast in-situ)SECTION X-X
(A) Reinforced concretelintel over window with
roof overhang
Concrete
beam with steel
reinforcement
Figure 3.14 In situ reinforced concrete lintels
Х
X
ELEVATION
(B) Reinforcedconcrete lintel
over opening
Precast pre-stressed concrete lintels
This is ihe most commonly used lintel in brickwork. The main advantages of
pre-stressed lintels are that they are light in weight and only a brick size
(110 x 75 mm) in section. They are inexpensive and available in standard
practical lengths. By themselves they are not particularly strong but in
combination with reinforced brickwork over it, forms a very successful beam
over openings.
The “pre-stressed" refers to ihe factory manufacturing process of the lintels
where the reiníorcing in the lintels is "stressed mechanically in a factory before
the mould, in which it is placed, is filled with a high density concrete. This
results in a very strong, sinall profile concreie “beam". See figure 3.15.
Steel reinforcing
Fine high-density
high-strength
concrete lintel
100
ok*
Figure 3.15 Precast pre-stressed concrete lintel
3.1.6 Brick arches
The main purpose of an arch is to support the weight over an opening in a wall
and to transmit this weight io either sicle of the opening. A brick arch consists of
wedge-shaped bricks built around a curve and arranged in such a manner that
they support each oiher and the weight from above. Ordinary bricks (not wedgeshaped) can also be
used in which case it requires excellent workmanship,
particularly when face bricks are used. See figure 3.16, showing wedge-shaped
bricks.
Radius
ELEVATION SEMI-CIRCULAR ARCH
Figure 3.16 Brick arches
3.1.7 Cavity walls
Use of cavity walls
Frequeni use is made of cavity walls as outside walls, particulariy in high
rainfall areas.
A cavity wall consisis of two skins (leaves) of brickwork, blockwork, stonework,
etc., with a cavity (space) ir-between. The main object of ihis arrangeinent
is to protect the inner surface of the wall from dampness wiven the exterior
is exposed to severe wind and rain. When the cavity wall is properly
constructed, dampness will only penetrate ihe outer skin, with the cavity
between the skins forming an effective barrier to water reaching the inner skin.
Another objective of the cavity is to provide an air space between the two
skins, to aci as a thermal and sound insulator. The thermal insulation value
of external cavily walls can be appreciable in comparison io that of ordinary
solid brick walls of the same thickness.
The 'wo skins musi be tied together to prevent buckling due to wind pressure
or to loads imposed by the weight of the structure and roof. A cavity musi be
ai leasi 50 mn and not more than 75 mm in width. Each skin must be at least
105 mm (inalf-brick) ihick at any level. Ties must be placed ai not more than
every 4 layers horizontally and 500 mm centres vertically.
Gavity wall construction
In figure 3.17 is shown at (A) the half-brick outer skin of brickwork; at (B)
the 50 mm wide cavity (air space); at (C) the half-brick thick inner skin of
brickwork; and at (D) the galvanised metal wall ties. A twist is formed at
the centre of the tie (or the tie is bent zigzag for its entire length) to preveni
the passage of moisture from the outer to the inner skin and to ensure that
it does not pull out of the brickwork joints. The end of the ties are fanned
out as shown and to prevent any danger of the passage of moisture, they
musi be kept free from mortar droppings during construction.
50
106
106
Galvanised
wall tiesD
Figure 3.17 Cavity wall construction
C Half-brickinner skin
B Cavity
A Half-brickouter skin
3.2 DAMP-PROOF COURSES
Special precautions must be taken to prevent moisiure penetrating a building
from an external source, or from one part of the siructure to another. iioisture
can become a problem when it: rises up walls from the ground,
flows down walls from parapets or chimney stacks above roof level,
passes through openings, orenters a building under pressure from below.
It is therefore necessary to provide a layer of impervious maierial at certain points.
This layer is termed a damp-proof course (DPC) and the actual site conditions
will determine the extent of DPC required.
The properties required of a damp-proof course are that: It should be impervious to moisture;
it should be tough enough to avoid damage when it is being laid and whenthe operations which follow
the laying of the DPC are being carried out.
Polythene sheeting is the mosi durable for ordinary work and is thus the product
in common use.
3.2.1 Horizontal damp-proof course
Figure 3.18 shows ihe horizontal da. np-proofing arrangements required for a
groundlevel wall anci floor for wei conditions. Figure 3.19 shows the damp-proof
membrane around windows required in a cavity wall in very wet regions.
to
Min 4 brick courses
110
50
***
Н.
110
H
A Concrete strip foundation
Brick foundation wall
C Ground backfilling
DNGL (Natural ground level)
E DPC (Damp-proof course)
F Horizontal damp-proof course
G Face bricks
H Half-brick leaves to form cavity wallCavity
1919
111114
Iік
L
J
M
230 min
#1
150 ,75,75L1
150
Min 500
*
+
3 25 12
One coat internal cement plaster
K Floor skirting
L Quarter round
M Final floor covering
N Cement screed
O Concrete surface bed or cover course
P
Concrete surface bed
Q Hard core
R Ground filling
Figure 3.18 Stripfooting with cavity wall and solid floor for wetconditions
NNNN
ANNNN
SINNE
NNNNN
SECTION A-A
Details for
facebrick
walls in
wet conditions
DPC
Concrete
lintel
DPC
under
window
sill
DPC
behind
outer
brick
skin
HE
FRONT ELEVATION
DPC under window sill taken
1/2 brick past openingSECTION B-B
.
Figure 3.19 Water proofing of window openings in cavity walls
3.2.2 Vertical damp-proof course
Vertical dpc is for protection against dampness to basements, or io other parts
of a structure which may be below ground level. Figure 3.20 shows an example
of this. The vertical waterproofing (A) is continuous from the normal dpc level
down to the waterproofing (B), passing through ine basement floor.
This method (often called tanking) should prevent dampness inside the building
but is not recommended in very wet regions where proper basement construction
should be followed.
NGL
Vertical damp-proof course
(A)(DPC)
Half-brick leaf as protection
of damp-proof course
(A)
Concrete foundation
NNNNNS
NNNNNNNNN
CZ
ZA
Figure 3.20 Vertical damp-proof course
Cavity wall
Horisontal damp-proof course
on surface bed
(B)
Concrete surface bed to receive
horisontal damp-proof course
(B)
3.3 FIREPLACES AND FLUES
When a iracitional fireplace is required in a building it imusi be of sound desigri
io ensure structural stability, funcionaliiy and fire prevention. See figure 3.21.
650
220
65 110 65
Figure 3.21 Fireplace and flue
450
oc
220
| 350 min.
Structural requirements
Chimneys, ilue pipes, hearths and fireplaces must be so constructed that: they will not be unduly
affected by heat, condensation or combustion
ignition of any part of the structure is prevented
smoke cannot escape into the building
ilue pipes are so placed and/or shielded that there is no isk of accidental
damage to the pipe or of danger to persons in or about the building
they are properly supported, and discharge into the open air
The flue and chimney
A flue musi be at least 150 mir in diameter, and must be lined to resist acids
and other by-products of combustion.
Flues may be lined with any one of the following:
rebaieci or socketec flue linings made from asbestos-cement or kiln-burnt
aggregate and high aiumina cement
glazed vitrified clay pipes and fittings
glass (vitreous) enamelled salt glazed fireclay pipes and fritings
3.4 ROOFS
Roofwork has to be designed in such a way that it is able to carry the weight of
the struciure, the roof covering, ceilings, workmen, wind loads and other dead
weight such as snow or hail.
3.4.1 Types of roofs
Figure 3.22 shows various iypes of roof structures whilst figure 3.23 provides roof
terminology.
Flat root
with parapet
Mono-pitch
Gable roof
Flat roof
with overhang
Lean-to
Gambrel roof (Brit)
Butterfly
or vee roof
Hipped roof
Mansard roof (USA)
Figure 3.22 Roof types
Clerestory roof
Pyramid roof
Mansard roof
Gambrel
Saw tooth or
south light roof
Jerkin head
Monitor roof
Parapet gutter
Ridge
Gable
Verge
Gable end
Lantern light
Gambrel vent
Box gutter
Valley
Gutter
Downpipe
Finial
Pyramid light
Domelight
Figure 3.23 Roof terminology
Parapet
Apron flashing
Spout (gargoyle)
Stepped flashing
Hip ridge
Hip
Eaves
Hipped end
Eyebrow dormer window
Dormer window
Lucarne
Skylight
Figure 3.24 shows the components of a iypical truss. Of particular importance is
the camber which is formed in the truss to allow for deflection io a horizontal
position once the truss carries the full weighi of the roofing and ceilings. The
various pieces (wood) of a truss are collectively known as members.
Top
rafter
King post
-Pitch
Bearing Tie beampoint
Overhang
Apex
Struts/webs
Splice
Nodes
Span
Camber for
downward deflectionwhen loaded
Figure 3.24 Roof truss components (members)
Sprocket
Figure 3.25 shows various configurations (types) of trusses. Only common truss
shapes are included here. However, trusses are versatile and complicated
profiles can be designed and manufactured, particularly so when factory
manufactured products are used.
NAME
King post
Queen post
Fink
Fan
FW
Double w
Triple w
King scissors
Queen scissors
Howe scissors
Double howe
Scissors
Triple howe
SCISSORS
Warren scissors
Double warren
Scissors
Modified scissors
Modified scissors
Modified scissors
Modified scissors
Modified scissors
Polynesian
or gambre
Polynesian
or gambrel
Mond-half
howe comp
Mond-half scissors
howe tension
Monc-half
scissors warren
MAX.
SPAN
(M)
16
16
16
7
7
6
9
10
13
13
18
4
6
5
6
CONFIGURATION
NAME
Polynesian
or gambrel
Polynesian
or gambrel
Simple attic frame
Queen post
attic frame
Howe attic frame
Vaulted ceiling
Vaulted ceiling
Vaulted ceiling
Vaulted ceiling
Bowstring
5. to 9 panels
Howe girder
Double howe
girder
Triple howe
girder
Inverted howe
Inverted
double howe
Mono pitch hip end
45° corner set
Hip type "A"
Hip type "B"
truncated system
Hip type "D"
(dutch hip)
Hip type "E"
Figure 3.25 Roof truss configurations (types)
MAX.
SPAN
(M)
16
10
14
14
13
18
18
18
6
10
10
CONFIGURATION
TITE
Figure 3.26 shows a number of eaves detailing and iruss hold down io l'esist
blow-off by wind.
Wedge
Diagonal
z bracing
2,8 mm x 40 mm Lg.
clout nails
38 x 114 wallplate
38 x 1,2 mm hoop-iron strap: (Or
galvanised wire strands tied around
rafters.) Built into 7 courses of
brickwork and nailed to the truss.
(Where trusses are supported on
concrete beams, straps are to be
cast a minimum of 400 mm depthinto the beam.)
Truss hold down - essential to resist the
uplift forces due to wind action on light roofs.
Figure 3.26 Eaves detailing and truss hold down
BUILDING CONSTRUC170M
3.4.2 The design of trusses
The design of trusses is based on the principle that the forces in the element meet
ai the nodes in such a way ihat wringing does not iake place. Trusses which are
bolted are more inclined to wringing ihan trusses connected in one plane with
inetal nail plates in a factory.
Traditionally trusses were made of rough timber, bolied together on site. In the
metropolitan areas this practice has been replaced by factory manufactured
irusses, connected at the rodes by metal nail plates, Lising selected planned timber.
Truss designs are calculated by a computer program in factory manufacturing,
optimising material utilisation and strength.
Tiled roofs are iypically erecteci with irusses spaced not more than 750 inm centre
io centre anci with galvanised iron roofs not spaced more than 1200 mm centre
to cenire. Overhangs generally do not exceed 800 mm.
Figure 3.27 shows the reaction of the various forces at the nodes (joints) in trusses.
V
Torsion
IHI
1.1
Gusset
Torsion
Gusset
Gussets both sides
Figure 3.27 Nodes of wooden roof trusses
Force
Force
Force
When designing and erecting trusses the following aspects should be considered:
Bonding
Bending in iruss inembers should be avoided by ensuring that loads, or
reactions to these loads, are appiiec to the frame by suitable arrangement of
the members. Some load, via purlins or battens or from water tanks, eic.,
which could cause bending are often unavoidable and must be allowed for
in the design of the members. If the truss is supported ai places which are
not node points, excessive bending will occur and the addition of furtirer
inembers inay be necessary to avoid bending.
Compression members (Struts)
Buckling may occur in long compression members (struts) which have a
length to breacith ratio greater ihan 50. The likelihood of buckling may be
enhanced by faulty timber and a-centrically applied loading. The rafter of a
truss is a compression member and is usually the meinber subjected to the
highest direct compression. Rafters are prevented from buckling sideways
by the purlins or battens fixed to them. Compression members can be
strengthened by bracing when their length to breadth ratio is too high.
Tension members
Unlike compression members, the size of a lension inember carrying a given
load is the same for all lengths and cross-sectional shapes of timber. The
size of the member in tension will usually depend on the jointing material
rather than on ihe force applied to the member.
3.4.3 Joints between members of trusses
There are two basic ways of joining the ineinbers of a truss together: Lap joints, which are formed by
overlapping the members and securing them
together with one or other of the following types of connectors – nails, bolts,
or toothed plate connectors. Adhesives should not be used for joints.
Butt joints, which are forined by cutting the ends of the ineeting inembers at
the correct angle to form a buti joint and by fixing gussei or splice plates
across the joint to tie the iwo members together. The plates are punched
metal connector plates with teeth or nails mechanically pressad into the ümber
on both sides of the joint in a factory. ivieta! gusset plates with pre-purched
holes for nails are also used for on-site applications.
Lap joints
Until about 15 years ago inosi trusses for single storey buiidings in South Aíica
have been constructed using ! eppec joints wilich have generally beer secured
together by nailing or bolting. Nailed or boiteci joints are the easiesi forin of
construciion and the cheapesi for lap joinis, but ihis method generally does
not coniorin with engineering requiremenis and consequently failures at joints
often occur. In adcition, lapping of the joint inakes it impossible to make the
truss in one plane and when erected, the truss members will inevitably be oui
--of plumb, especially iſ the pitch of the truss is low. This is often apparent in
the skewness of eave sprockets.
Permissible safe load values for nails and bolts for various strengihs of timber
together with minimum ecige disiances and spacing, are given in the National
Building Regulations (SABS).
Failures of nailed or bolted joinis may be due to: overstressing of the timber in bearing against the nail
or bolt.
the nail pulling out (i. e. insufficient number of nails or volts to resist the
forces at the joints).
splitting of the timber ai the nail or boli hole (this imay occur wher the
nail or bolt is driven or fixed too close to the edge of the timiser or the
holes are too close together). shearing oui of a piece of inber.
As a result of the failures, there will be slip at the joint with settlement of the
truss on to intemal cross-walls or redistribution of loads through purlins or
battens via the rafters to the wall-plate. The roof irusses üven no longer
perforin their design iunction and loads may be transferred to internal walls
noi originally designed to be load-bearing. Trusses with overloaded joints
are subject to severe creep deflection and there is little or no elastic recovery
on removal of the load.
While it is unlikely that the truss will often be fully loaded to the design value,
the nails and possibly one bolt which are provided at the joints for trusses
construcieci on site are toially inadequate. li is no wonder thai excessive roof
deflections, especially over rooms spanning the full width of the building, are
often to be seen.
Butt joints
As mentioned previously, buit joints for trusses are formed by square cutting
or bevelling the end of the member to the meeting angle to ensure firm contaci
at the abutting surfaces. The meinbers are then fasteneci together with
punched metal plates and provide trusses which are superior to those with
lap joints.
Several manufaciurers in South Africa imarket nail plates of various
configurations for which design data have been deterimined for use with
graciec SA pine to form joints for roof trusses. See figure 3.28.
104)
:: ::::
Example of a punched metal nail-plate connector
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ըմընըմընընլ Ս.
(0) 07նընդUը |
Example of joints
Connection of trusses
Truss hanger
Figure 3.28 Punched metal plates
Licensed truss fabricators
BUILDING CONSTF: UC770N
The inanuíacturers usually iicence a truss fabricator to assemble roof trusses
with their nail plates in accordance with approved designs, and they provide
a design service for trusses of unusual configuration or loading.
"The trusses assembled with nail-plate connectors are generally factory
assembled in jigs. Large russes are sometimes transported in two sections
and joined together on site. It is essential that the manufacturer's
recommendations for joining on site be closely followed as poor assembly can
seriously impair the high performance which can be expected from factoryassembled trusses. Erection
of the trusses on site should also be undertaken
with care as bending of the truss may cause nail plates to be loosened or
pulled out. As the forces in the inembers of the truss meeting at a joint are
of different values, it is important that the plates at a joint be placed strictly
in accordance with the design requirements so that there are sufficieni nails
in each to transfer the forces effectively and safely. Buti joints at the end of
compression members should be reasonably close fitting as usually only pait'
of the force is designed io be transferred through the nail plate at compression
joints, the remainder being transferred at the butted timber faces.
3.4.4 Bracing and fixing of roof structure and components
Distortion and failure of roofs is often due to iack of proper bracing of the roof
siructure. Hipped ends will supply rigidity to the whole roof structure and on
sheeteci roofs the large sheets fixed firmly io the framing wili usually supply
sufficient bracing. Small roofing units such as tites and slates will contribute little
if any to bracing.
On long rooís with gable ends, bracing must be supplied to prevent racking or
tilting of the frames. Temporary bracing is required during erection to keep the
trusses veriical and to stop buckling. Gable walls which are not buttressed should
not be used to stabilise the roof structure."
Rafter and tie bracing
Large roof sheeis fixed firmly to the framing via the purlins provide adequate
bracing íor the rafters. Diagonal bracing in the plane of tire rafters musi,
however, be provided for roois covered with small rooſing units.
At each gable end of the building, bracing inembers should be nailed to the
underside of the rafters at an angle of approximately 45 degrees to the line
of the rafiers and extend from the well plate to the ridge line.
BUXOING PRACTICE - VOLUME 1
Suction (uplift), especially on low-pitched roofs with lightweight coverings, may
induce compression in the tie of the truss. Because of its length and small
lateral wicth, ihere will be a tendency for the tie to buckle.
Ceilings construcieci with brandering anci sheet materials or iongued and
groovec boards will provide adequate bracing for the tie but false ceiling
constructions consisting of inverted "T" meta! stringers and loose infill panels
will have no stiffening effect and, where deemed necessary, tie bracing ai
each end of the building should be nailed over the top of the tie beams at an
angle of 45 degrees from the comer of the building.
Long web (strut, bracing
Long compression web inembers (struts) in trusses will require bracing when
their length to breadth ratio is greater ihan 50. Cross-bracing members at
approximately 45 degrees over several struts with a runner connecting all
struts to this braced section should be provided.
Gable bracing
Long, nigh gable walls require bracing against wind forces which would tili a
gable with consequent cracking at its base. It is therefore advisable to stabilise
high gabies by building up a buttress in brickwork from longitudinal walls, if
these are conveniently situateci, and to free the roof structure froin the gable
brickwork. Alternaiively, high gable walls could be braced by timber members
extencing down to the wall plate.
Fixing
When trusses have been erected into position and before final ixing, the
following points must be checked: All trusses should be vertically plumb and without bow.
Asymmetric trusses, such as cantilevers must be instailed ihe richi way
round.
Trusses must be spaced according to the instruciions.
Trusses must not have been cut or drilled at any time.
Wall plates must be firmly fixed to supporting walls.
The irusses may be levelled using hardboard shims. Wedges which
encourage the truss to tili over should not be used.
If all the above points are satisfied the irusses inay be fixed by skew nailing
them to the wall plates. The trusses must be held down to the wall as detailed
previously
3.4.5 Hipped roofs
Two basic methods of hip framing are used in South Africa.
Traditional method - hip rafter's
The traditional method of hip forming is to use heavy hip rafters (see figure
3.29). Proper design and construction of a hip requires careful consideration
if a stable and economical construction is to be achieved. There is considerable
interaction between all members of the roof and this largely accounts for the
relatively small number of failures despite the higir incidence of unsatisfactory
framework
Strengthened truss
Figure 3.29 Hip rafters
Heavy hiprafters
Hip trusses
For large roofs hip trusses may be required in place of hip rafters. The
configuration of the hip truss will determine whether the load will be casi on
to the apex of the main truss or on to its tie, and the connections at these
joints must be designed accordingly. Special truss hangers are availabie for
this purpose.
Strengthened truss
Figure 3.30 Hip trusses
Hip truss
3.4.6 Valleys
It is probable that only a small percentage of valley construciion in T-shaped
buildings are adequately performed as the principles of valley construction are
generally not understood. This usually results in the valley member feing supported
on internal walls, which inay or inay not be accepiable, depending on winether
these walls are able to carry the load.
The design to be used will depend on the layout of the building and the support
conditions available. Where there is no interna: wall to support the framework, the
configuration would take the form as shown in figure 3.31.
Protrusions through ine roof such as chimneys and vent pipes should not be
placed close to valley gutters. Special valley tiles inay be used on roofs with a
pitch greater ihan 35 degrees. Corrosion-resistant meial valley gutters should
comply with the detail shown in figure 3.32.
Provision must be made for screens to guard agair: st blockage of valleys and
internal (box) gutters iy hail in areas where this is a hazard.
The arrangement of trusses to form valleys is extensively used by the nail-plate
truss manufaciurers and provicies an easy and cheap imethod of construction.
1st Valley = Truss spacing x 2
3rd Valley = Truss spacing x 6
5th Valley = Truss spacing x10
Last valley truss next to
girder/full standard truss
is always less than a truss
spacing away
Figure 3.31 Valley trusses
Standard truss "A"
Standard truss "B"
2nd Valley = Truss spacing x 4
4th Valley - Truss spacing x 8
6th Valley = Truss spacing x 12
Roofing tiles
BattenPacking tiling
fillet
Metal
gutter
Figure 3.32 Valley gutter for tiled roofs
Waterproofingunderlay
Jack rafter
Valley board
Valley rafter
3.4.7 Gutters
The size of the gutters required will vary for different rainfall intensities. In the
areas where the rainfall intensity is known to be high, the gutter size and downpipe
arrangement must be sufficieni to avoid serious flooding (overflowing) which may
cause damage or damp-penetration to or through other parts of the building.
SABS Code of Practice 021 deals with the drainage of roofs. Table 3.1 gives
recommended sizes of gutters and downpipes for different areas of roof in South
Africa,
Table 3.1 Sizes of gutters and downpipes
Area of roof
drained (m2)
15
25
40
60
80
100
125
Size of gutter (mm)
Half-round
100
125
150
Rectangular
125 X :00
150 x 100
200 x 100
Size of downpipe (mm)
Round
100
Rectangular
100 x 100
100 x 100
125 x 100
Source: SABS Code oí Practice 021 (1973)
Details of chimney and abuiment gutters are shown in figure 3.33. Box gutters
draining water from the rooi have a high leakage risk and great care musi be talen
to ensure aciequale size and good construction. A minimum slope of 1:200 is
advisable to ensure proper drainage of box gutters. Box gutters made of galvanised
sheet steel are liable to give trouble at soldered and riveted joints and are subject
to corrosion problems and should be given a protective pair coating on both sides,
repainting the inside at least once every three years.
150 mm from
top of tile
Flashing
Et
75 mm min.
ELEVATION OF CHIMNEY
Flashing 150 mm wide
150 mm
PLAN OF CHIMNEY FLASHING
DETAIL OF CHIMNEY GUTTER
150 lap
125 mm or 150 mm flashing
depending on shape of tile
Approx. 200 mm wide gutter
Metal cover flashing
Approx 200 mm depending
on batten gauge
Gutter
Not less than
150 mm except for
pantiles 230 mm
BoardingTile
Cleat
- Trimmer
- Rafter
Between rafters
25 mm or 150 mm flashing depending
on shape of tile. End cut to shape
of tile and bent into groovesFLASHING ON SIDE OF CHIMNEY
Figure 3.33 Chimney flashing and gutter for tiled roofs (alsoapplicable to other roof coverings)
Rainwater discharge from higher roofs should not discharge on to low-slope roofs
unless suitable means are provided to prevent the possibility of leakage. Discharge
acijacent to laps between sheets should be avoided.
3.4.8 Roof coverings for pitched roofs
Roofing materials
The materials generally used for covering of pitched roofs are the following,
of which fixing deiails are shown in the stated figures:
Concrete roof tiles (figures 3.34 and 3.35)
Asbestos cement roof sheeting (figure 3.36)
Slate roof covering (figure 3.37)
Pressed steel roof tiles (figures 3.38 anci 3.39)
Trough sheeting with secret fixing (figures 3.40 and 3.41)
Ribbed metal roofs (IBR) (figure 3.42)
Batten
[ile
Clip
A
(used in areas
with high windscould also
be nailed through
top of tile)
305 mm
Detail of clip
Tilting batten
First tile + 30 mm
from outside edge
MN
End batten: 38 mm wide x 50 mm deep minimum
Figure 3.34 Concrete roof tiles
C
BURSING PRACTICE - VOLUME 1
Roof batten
Interlocking tiles
X
Side seal on tiles
SECTION X-X
Plastic membrane on trusses
Tiles
Membrane
Figure 3.35 Concrete roof tiles with slope < 26 degrees
Main fixing
8 o fixing bolt
416
906
5
100
BUILDING CONSTRUC110M
Avarage effective cover width 600 mm
Overall depth245 mm
Nominal thickness8 mm
Galvanised steel cup washer
Grey plastic washer
906
Main fixing
Cup washer
under nut
or head
Additional fixing point
Main fixing points are always positioned on high corrugations as indicated
Main fixing bolt
Timber filler piece
Main rafter
Cover flashing
Metal flashing
Asbestos-cement or timber supports
Figure 3.36 Asbestos cement roof sheeting (Canalit)
90 mm lap
610 x 305
centre-nailed
slates
VELANA
13 mm clearance
610
Gauge260 mm
25° pitch
375
Figure 3.37 Slate roof covering
Gutter
70 mm
Fascia
Gable and cover strip
60 mm
Timber
barge board
Gable end
Tie beam
57 57 mm
DETAIL Y
Timber
barge board bearer
Half-round
ridge tile40 x 20 battens
50 x 20 counter-battens
at 375 mm centres
Untearable felt on
insulation board
Half round ridging
Battens 38 x 38 mm at truss
apex fixed 57 mm both sides
Gable wall
Figure 3.38. Pressed steel roof tiles
38 x 38 roof batten
HIP
VALLEY
Tiles must be cut
and fitted
Jack rafter
Bearer
Hip rafter
Sheet valley tining
Continuous bearer
fixed between rafters
Trimmed rafter
Valley rafter
Figure 3.39 Pressed steel roof tiles (continued)
NNN
Female rib* 5 mm
42 mm
Centre rib
5 mm
148 mm
406 mm cover width
Cover flashing
Under flashing
Upward bend
HEAD WALL FLASHING
L
SIDE FIXING
Male rib
Ooo
Die
Punch
String line
Male rib
IVANT
45 mm
Cover flashing
Under flashing
Self-tapping screw
SIDE WALL FLASHING
Direction of laying deck
Clip
Figure 3.40 Trough sheeting with secret fixing
Female rib
Saw cut 13 mm deep
Decking stop ended
Galvanised screw on nail with 25 mm
soldered lead washer 2 400 mm vlc
Rib cap
RIDGING ALTERNATIVE 1
Rib slots notched on site with notching shear
Galvanised screw or nail 1 200 mm víc
Timber packing piece
140
127
25
59
MAX:
RIDGING ALTERNATIVE 2
50
Figure 3.41 Trough sheeting with secret fixing (continued)
Ridge covering
686 mm
Ridge plate detail
Ridge plate
VALLEY GUTTER DETAIL
Figure 3.42 Ribbed metal roofs (IBR)
Roof screw
Toothed ridge
filling piece
Foam rubber filling piece
Roof screw
Roof batten
610 mm valley gutter
Flashings
BUILDING COHISTAUCTION
Flashing work is to be executed very workınanlike as it is the mosi cominon
cause of roof leaks. The actual turn-ups and caulking into walls with a strong
sanci: cement mixture (1:3) go a long way in preventing leaks. Detail sketches
are given in figures 3.43 to 3.48:
Fascia
Cap flashing
Roof tiles
Ext. wall
Battens
TOP OF MONOSLOPE ROOF
Figure 3.43 Cap flashings on top of monoslope roof
HHHHH
Battens
Roof tiles
Sprocket ends
External wall
Cap flashing
-Fascia
TOP OF ROOF WITH SLOPE TO ONE SIDE
Figure 3.44 Cap flashing at lean-to roof with concealed gutter
BUZDING PRACTICE - VOLUME
220 Gable wall
Roof tiles
HI
Battens
Cap flashing
Fascia
Figure 3.45 Cap flashing at gable and overhang with tiles
RIBBED SHEET METAL GABLE END
F
Тв
Alm
A 38 x 152 mm SA pine or 15 x 150 mm cementfibre barge board nailed or screwed to B
B 50 x 76 mm SA pine roof batten
C Sheets fixed on edge
D 38 x 114 mm SA pine truss rafter
E One brick wall
F Mortar filling
А
Figure 3.46 Cap flashing at gable end overhang with ribbedmetal sheets
Cover flashing
Under flashing
Roof screw
Upward bend
HEADWALL FLASHING
Side lap screws
Self-tapping sheetscrew
on galvanised washer
on bitumen washer
at laps
Prevailing wind direction
Cover flashing
Under flashingSelf-tapping screw
SIDEWALL FLASHING
Hexigon head wood drivescrew on
galvanised washer on bitumen washer
Roof screw
Figure 3.47 Ribbed metal sheets fixing and flashing details
CONCEALED GUTTER
80
40 min.
Cover flashing
Metal gutter
220 min.
Back gutter
Gutter size to be
in proportion to
exp ted water flow
Joint raked out 50 mm and pointed after
installation of cover flashing
Slates
Cover flashing
Overlap 50 mm min.
Soaker flashing
Extension over slates 75 mm min.
Figure 3.48 General flashing details
FRONT FLASHING
150
Edge is lipped up
DETAIL OF METAL SOAKER
3.5 CONCRETE, REINFORCING AND FORMWORK
3.5.1 Concrete
Composition and use of aggregates for concrete
Concrete is made by mixing the following ingredients in specific ratios to
obtair the requireci strengths:
cement
waterthe aggregates (crushed stone and sand)
The aggregates are inixed by hand or imachine. The "iype" (strength) of ihe
concrete is usually described by volume, say 1 (cement):3 (sand):6 (stone).
The larger the cement content, say 1:2:4, the stronger the mix. The cement
and water forms a "glue" which sets through a chemical process called
hydration of cement. If too much water is added the "glue" becomes too
diluted, thus producing a weaker concrete despite the volume of cement. The
aggregates could also be selected by weight as there is an obvious relation
between volume and weight. Mixing by weight is known as weight batching.
Aggregates occupy inuch of the volume of concrete, therefore the selection
of suitable material is very importani.
Good aggregaies have the following qualities: Hardness. The aggregate should be at least as hard as the
hardenedi
cement which binds it together wihen the concrete has hardened (set).
The particles should be free from coatings of clay, which would prevent
proper bonding (gluing) of the material.
Durability. Aggregates should not contain deleterious materials that arelikely to decompose or io change
in volume when exposed to the weather:
All aggregates should be clean and free from organic impurities. Dirty
aggregates make poor concrete.
Aggregates are classified as fine or coarse.
Fine aggregate refers to naiural sand and crushed stone, that pass through a
5 mm sieve.
Coarse aggregaie is crushed or pebble stone, that is retained on a 5 mm
sieve.
Sands and crusived stone (granite, basalt, and the harder types of limestones
and sancsiones) are commonly used as aggregates. The maximum size of
aggregate is determined by the intended use. For reinforced concrete, it must
be such ihat all the aggregate will pass readily beiween the steel reinforcing.
Coarse aggregate used for this purpose generally has a maximum size of
19 mm. The size of aggregate may be increased for foundations and mass
concrete work.
Aggregates should contain particles ranging in size from the largest specified'
(say 19 min) to small. The proportions of the amounts of the different sizes
are conirolled by using various sieves with appropriate imeshes. This grading
is very importani; ihe fine aggregate should fill the spaces between the coarse
aggregate, leaving the minimum percentage of voids to be filled by the cement.
Thus the relative proportions of small to large should be such that a solid mass
is obtained when mixing it.
Concrete mixes
The iwo essential properties of concrete are durability and strength. Both of
these are closely related to density. In general, the denser the concrete the
greater its strength and the higher the percentage cement, the greater the
strength.
Sufficient sirength is necessary to carry the loads, and sufficient density to
ensure that the concrete will be impervious to water and that it will provide
adequate protection to the reinforcemeni.
The proportioning of the aggregates, either by volume or by mass depends
io a great extent on the quantity of concreie to be mixedi. As it takes longer
and is more expensive (but more accurate) to mix by mass, it is common
practice to batch by mass on large projects and on small projects by volume.
The quality of concrete produced by either method will depend on the quality
of the supervision, but it is generally accepted ihai mass baiching produces
a inore consisteni quality of concrete as it is usually undertaken by utilising
batching plants which are more consistently controllable.
Coment
Poriand cemeni is the usual material used and is manuíactured in South Africa
to conform to SABS specifications. This ensures that the cement has passed
iests for ſineness, chemical composition, sirength, setting time and soundness.
There have however been an alarning increase in cerrent types being
introcluced to the in. arket and extreine care should be exercised to ensure
that the correct choice is inade for each application. Legislation coes,
however, exist io ensure ihat the various "types" of cement conform to the
SABS specification.
Setting and hardening inust not be coníused. Setting refers to the süiffening
of the cemeni; harciening refers to the development of strength. The setting
time ior Portlanci cement is 30 minutes for ihe initial set and 10 hours for the
final set. The strength of the concrete (hardening) however keeps or increasing
for years, provided ihai il is kept wei. Temperature also plays an importani
role as the sirengih increases with higher temperatures during seiting.
The proportion of water in the inix is controlled by specifying the ratio of water
to cement by weight. This is termed the water: cement ratio. Other things
being equal, the strength of the concrete depends on the relative proportions
of water and cement - ühe higher the proportion of water, the weaker the
concrete.
The amount of water used should be the minimum necessary to give sufficieni
"workability" for efficient consolidation of the concrete. In practice, the ratio
will vary according to the inaterials used and the nature of the work.
Mixing and laying concrete
Properties and mixing
Concrete shouid be made by mixing cemeni with clear fine and coarse
aggregates. The proportions vary for different classes of work, from 1 part
of cement, 2 parts of sand and 4 parts of coarse aggregate, by volume
(1:2:4) in reinforced concrete construction, to 7 part of cement, 3 parts
of sand and 6 paris of coarse aggregate, by volume (1:3:6) for other kincs
of work. Laboratory iesting of reinforced concrete is required and 150
mm x 150 mm x 150 mrn test cubes are made for each portion of the
structure placed at a time. Test cubes are crushed on 7 days and 28
clays after the placing of concrete and the strength is measured in Pa.
The expected 7-day strength is 60% of the 28-day strength, thus
confirming within a week if the required 28-day strength is likely to be
obtained
A imechanical mixer is lised on most jobs because mechanical mixing
gives results that are more satisfactory and uniform than hand mixing.
In many inachines the quantity of water can be regulated by an automatic
Gauge. After the materials have been placed in the drum and the water
added, the drum should be rotated for noi less than three minutes. The
mixing water should be clean and fresh. Ti it is suitable for cirinking, it is
suitable for concrete, otherwise do not use it.
“Reacıy-inixed" concrete inay be supplied by truck or transit inixers,
operating frora a centrai batching plant. The cry materials are put into
ihe mixing drum and, as the mixer gels near the site, the water is added
*
and the mixing started. Ready-mixed concrete is useful where ihe site
is restricted and storage space limited.
Placing of congreic
it is important that the concrete be placed in its final position before the
initial set takes place. The usual requirements are that the concrete be
placed in position within 30 minutes of mixing (adding of water) and thai
it is noi disturbed after it has been placed.
Gonsolidation
The object of consolidating the concrete, whether by hand-tamping or
by imechanical vibration, is to achieve maximum density by forcing all
ihe air out of the concrete. The chief advantages of vibrated concrete
are:
drier inixes (less water in the mix) inay be used, giving a concrete
of greater durability and higher density and strength for a given
cemeni content;
the fornwork may be removed earlier irom vibrated concrete than
irom hand-tamped concrete.
The vibrator units may be secured to the forms, or internal vibrators may
be placed in the concrete. To be effective, external vibrators must be
firmly secured to the formwork, which must be sufficiently rigid to transmii
ihe vibration and strong enough not to be damaged by it. The vibrators
are switched off when all the air has escaped from the concrete.
Vibrators of the internal or poker iype are pushedi vertically into the
concrete at poinis about 500 im apari, and gradually withdrawn when
air bubbles no longer coine to the surſace.
Construction joints
Construction joinis are unavoidable ai the end of each day's work. Care
should be taken when laying is resumed that a good bond is obtained
between the exisiing and the new concrete. When new concrete is to
be placed on top or adjacent to existing concrete, any laitance should
be removed.
Laitance is a scum oí cement and very ine material from the aggregates
that forms on the surface of the concrete. A hardened surface should be
wire-brushed or, if too hard, hacked io expose a fresh face. A! loose
particles and dirt should be removed by washing with clean water and,
beſore concreting is resumed, the surface should be given a coating of
cement grout - a fluid cemeni and water mixture.
Guring
Concrete hardens as a result of chemical reaction (hydration) between
the cement and water. This process continues so long as the temperature
is favourable (high) and sufficient moisture is present.
The sirength of concrete increases with age if curing conditions are
favourable. The increase is rapid in the early stages, then continues
more slowly for an indefinite period. Curing is a method of increasing
the durability of the concrete by covering all its exposed surfaces with
sacking or sanci, which should be kept damp for at least seven days.
Waterproof paper may also be used, provided that it is kept in close
contact with the concreie surface and that the edges are held down to
preveni moist air escaping.
3.5.2 Reinforcing
General principles
Definitions
The term reinforced concrete is applied to concrete in which steel is
inserted for the purpose of strengthening the structure by enabling full
use to be made of the strength of the concrete in compression and the
sirength of the steel in tension,
In reinforced concrete the proportions of steel and concrete are so
designed that the stresses will be distribuied properly between ihe two
inaterials, having regard to their respective safe resistances. The forces
which tend to pull the particles in the material away from one another
produce tensile stresses. Those which tend io compress the particles
produce compressive stresses. The tendency of the particles to slide
one on the other produces shearing stresses.
Object of reinforcement
The primary object of reinforcement is to reduce the cost of construction.
Concrete has a low tensile strengih, and the amount of it that would be
required in structures subjected to tension would be very large. It is
therefor more economical to use sieel to resist tensile stresses. When
concrete members are reinforced they can be made inore slender in
section.
D
BUICING PRACTICE - VOLUME 1
On the other hand, the compressive strength of concrete is comparatively
high, and in most cases it is cheaper to use concrete to resist compressive
stresses. Consequently, a very economical and comparatively light
structure can be obtained by combining the two inaterials and designing
the siruciure so that the compressive stresses will be mainly resisted by
the concrete and the tensile stresses by the steel. This is the principle
on which reinforced concrete construction is based.
Concreie members that primarily resist compression, such as columns
and piles, are also reinforceci by steel to beiter withstard bending and
the effects of shocks than when unreinforced.
The embedded bars, tied together laterally by small diameter stirrup bars
are prevented from bending sideways and are thus able to take a portion
of the downward load.
The mass of concrete is held together by üne reinforcement, which forms
a cagework around it and ihus can suppoit a greater load than would
otherwise be the case.
Protection of stool from corrosion
There are many cases on record in which steel has been found in perfect
condition, aimost free from corrosion, on being removed from concrete in
which it had been embedded for many years. The danger of corrosion
(rust) is slight if the concrete is property made and the steel is a sufficient
distance from the surface. The normal requirement (terminology) is that
reinforcemeri should have a sufficient "cover" io prevent rusting and to
ensure that it can fulfil the intended purpose without "bursting" out of the
concrete.
* Bonding of reinforcementThe reiníorcernent in beams and slabs consists of round bars, with the ends
of the bars hook bended in order to increase ihe resistance to sliding.
Another practice is to use high tensile steel bars, which are twisted, to provide
a imechanical bond with the concrete. In addition to bars of this nature, there
are bars with a portion of their length bent upwards, which, in addition to
preventing diagonal cracks, offer a considerable resistance to sliding.
The main principle involveci is that reinforcing erbecided in concrete, bonds
completely with the concrete as a resuli of the fact thai concrete shrinks when
drying, thus “gripping” the reiníorcing over its entire surface. The concrete
anci ihe stee! thus forms a "reinforced concrete" meinber acting as an eleineni
of ine structure.
Golumns
The reiniorcement in a concreie column serves primarily io bind it together in
such a way that it becomes effectively a iromogeneous member, with the two
materials acting together when subjected to a load. Practical considerations
show that a syslem of longitudinal bars, braced with light stirrup bars in the
form of loops or a spiral, gives the inost satisfactory results. Columns with
spiral (helical) reinforcement should have at least six vertical bars within the
spiral. All other columns should have at least one longitudinal bar near each
corner of the column. At all joints in longitudinal reinforcement, the bars should
be overlapped for a length equal to iwenty-four times their diameter. This lap
joint is as effective as if the bar is continuous due to the concrete shrinkage
averting any slip. In figure 3.49, the stirrups (A) (ties) are placed at intervals
which should not be ess than the least of the following:
the easi laieral dimension of the column;
twelve times the diameter of ihe smallesi longitudinal reinforcing bars;
300 min.
Stirrups A
Stirrups A
PLAN
Figure 3.49 Column reinforcement
Main column reinforcement
Figure 3.49 also shows the arrangemeni of ihe reinforcement stirrups. Stirrups
should be so arranged as to prevent ouiward bending of verticai bars between
ühe stirrups. As compression increases on columns, they can bursi" outwards
ii sufficient stirrups are noi provided.
Beams
in the case of beams, the primary reinforcement is that which is introduced
to strengthen the portion of the beam which is in iension.
Boin ühe concrete and reinforcing in reinforced-concrete beams are usually
united with the concreie and reinforcing forming ihe columns. A beam being
fixed ai the end's, iends when loaclec, to assume ihe form shown (exaggeraiec)
in figure 3.50 (A). Not only is there tension ai (a) in the lower poriion of the
beam in the centre of the span, with a corresponding compression in the
upper portion (d), but the stresses are reversed in the part of the beam near
the supports, where there is tension in the upper portion as shown at (b).
Further, there is what is termed diagonal lension, tending to produce cracks,
running naturally at right angles to the direction of the stress (c). Although
this diagonal tension (which increases toward the supports oí a beam) is
present in both supported and fixed beams, and in all materials, it seldom has
to be taken into account in materials other than concrete which are usually
of sufficient strength to counter it, as ii is not composite materials like reinforced
concrete (composed of steel reinforcement anci concrete). However, concrete
is so weak in tension that, in addition to the reinforcement at the points where
the beam is subjected to ordinary tension, further reinforcement against
diagonal tension must be provided. One method consists of introducing speciai
bars attached to or forming pari of the lower tension bars, inclined toward the
supports at an angle of 45 degrees. Another widely used method consists
of carrying up one or more of the lower tension bars to the top of the member,
as shown in figure 3.50 (B). This treatment achieves a double result: The bars in their inclined position
resist the diagonal tension.
When carried along the top portion of the beam near the supports, the
bars resist the tension in this portion of the beam and usually renderunnecessary the provision of any
further reinforcement in it.
In the cross-section through the centre of the beam shown in section Y-Y
of figure 3.50 (B), the four bars (a), (b), (c) and (d) are shown at the bottom
of the beain where the tension is greatest.
In section X-X of figure 3.50 (B), which is a cross-section near the supporis,
two of the bars (a) and (b) are shown to have been brought to the top of the
beam by running them up at an angle, as shown at (a) and (b).
In figure 3.50 (B), the bars (c) and (d) are being carrieci inrough horizontally
for ine entire length of the beam.
х
c'd
X
Loading,
(weights)
booba
ai
Do
Jinni
A: SECTION THROUGH BEAM
Y
a
b
с
b
B: SECTION THROUGH BEAM
Figure 3.50 Beam reinforcement
a
с
SECTION Y-Y
a
SECTION X-X
Slabs and beams
The previous remarks about beams apply, almost without exception, io slabs.
As in beams, it is necessary io providie for the effect of reversal of stresses
ai ihe supports. The commonest instance of this occurs at the junction of a
slab with a bear.. it is customary to carry every other, or at least every third
one, of the reinforcing bars well over to the opposite side of the main beam.
This is shown in figure 3.51. The bars which are carried over being shown
at (a) and (b), and those which run ihrough horizontally at (c) and (d).
In practice, these bars would be inserted in the concrete in the same
horizontal plane and at the same distances from the top and lower faces of
the concrete but, for the sake of cleamess, figure 3.51 shows them rurning
above and below one another.
The inclinec portions of these bars also increase the resistance of the concreie
to diagionai tension. Floor slabs are occasionally reinforced in both direciiors.
When so constructed they are considerably stronger than slabs with their main
reinforcernent in one direction only.
Wall panels, which, iogeiher with the framework of columns and stanchions,
form the enclosures of a building, are ciesigned on much the same principles
as are slabs. Instead of floor loads, these panels have to resist the vertical
load (concrete) on it and the tension (steel) due to wind pressure, which varies
according to the height and situation of the building. The reinforcing bars of
wall panels are usually vertical, out additional bars running horizontally are
provided to distribute the load.
a
Figure 3.51 Slabs and beams
3.5.3 Formwork
b
introduction
Concrete constructional meinbers (columns, walls, siabs, bears) require a
mould in which it can be cast to the required shape. These moulds are
generally calleci formwork or shuttering. Formwork inusi be assembled and
erected in such a manner as to be capable of withstanding the mass of the
wet concrete, the forins themselves and the loads caused by the men and
equipment pouring concrete on, or into, the formwork, and the vibrating of the
wet concrete. The formwork inust be constructed in such a manner as to
prevent the leaking of fine particles of sand and cement ugh joints while
the wet concrete is poured and vibrated. The formwork must also be erecied
in such a fashion thai it is easy to disinantie when the concrete has set.
Materials
Formwork is generally consiructed iro. n timber, steel or fibreglass. Steel,
fibreglass and planed iimber give a smooih finish to ihe concrete.
The high cost of timber has led to many inventions and paients for steel
formwork with the object of reducing or avoiding the lise oſ timber.
This acivance is particularly obvious in the area of ihe suppoit iimbers,
where these relaiively costly pieces of timber have been replaced with
adjusiable steel siruts, column clamps and floor centres. The quality of
shuttering (iormwork) used to hold concrete accurateiy in position until it
has set sufficiently is very important as it is labour intensive, and concrete
and reinforcing are expensive.
The requirements for good fornwork are: strength ard rigidity;
tight joints which do not leak when concrete is poured and vibrated;
provides clean, smooth surfaces;
ease of erection and dismantling (also called stripping or striking); cost-effectiveness (determined by the
number of times used).
The use of steel forms avoids wastage of timber and the expense of cuiting
and fitting timber forin. s. Steel forms are made up in standard units, panels
and sections with interchangeable connections so that any two or more may
be locked together. Steel forms are expensive at first cost, but they can be
used repeatedly and are cheaper in the long run. Because they are easy to
dismantle, work can be executed more quickly. They also produce a better
surface on the concrete than do timber forms. For intricate "once-off" members
it is usualiy cheaper to use timber to manufacture high quality formwork.
Fibreglass, bonded with resin or resin-based adhesives, is widely used as
formwork for certain applications. It is lighter than steel and is particularly useful
as shuttering in profiled work such as coffer slabs, and it provides a very
smooth finish.
Rolcase agents
Before reinforcing is fixed against formwork or any concrete is poured onto
or into formwork, a release agent should be applied to the formwork. Release
açents take the form of oils, greases, paints and lacquers and provide a film
on the face of the formwork which prevents the concrete from adhering to it.
Therefore the forinwork is easier io strip and clean and inany more re-uses
are attainable.
Removal of formwork
The formwork of beams and slabs are designed so thai the sicies may be
removec leaving the bottom and strutting undisturbed while hardening is
effected. In other classes of work, all the formwork is usually removed at one
time. It is essential to leave the formwork in position unül uniform, continuous,
even cirying and sufficieni hardening has taken place.
The length of time required depends on the ieimperaiure of the air, the
characier of the member, the setting properties of the cement, and the mass
A
which the member carries of the finished structure after stripping of the
formwork. The structural engineer provides the earliesi stripping days for
the difereni members, depending on each specific situation.
Examples of formwork
Typical details of standard formwork are shown for slabs – figure 3.52 (A),
columns – figure 3.52 (B), walls – figure 3.52 (C) and beams – figure 3.52
(D).
FLOOR SLAB FORMWORK
Steel panels
or wood
boarding
B
COLUMN FORMWORK
Standard
steel
panels
Steel
support
centres
or wood
beams
Column clamps
Figure 3.52 Formwork
Standard
steel
panels
UJOUR
C
WALL FORMWORK
D
BEAM FORMWORK
ENTE
Standard
steel
panels
Tie rod
Reinforced concrete finishes
Depending on the type of building, various design options are available for
reinforced concrete. The type of finish required to the underside, edges,
coiners and general surfaces will determine the quality of shuttering required.
For concrete receiving further finishes, ordinary shuttering is used. Concrete
which is not going to receive further treatment and which forms part of the
aesthetic appearance of the building requires the most expensive shuttering,
called smooth formwork or off-shutter finishes.
Fiat slabs
Ordinary flai slabs are used in light sirl: ctures such as small office and
apartiment blocks, houses and schools. The coluinn spacing is typically not
far apart, usually noi more than 4 in in one direction and 8 m in the other.
Sounci isolation on these structures are not very good and it is therefore
seldom used on prestige projects. The underside (soffit) can just be painted
if the shuttering is adequate, for example in parking garages or it can receive
plaster, or other finishes. See figure 3.53.
The loading capacity and column spacing of an ordinary fiat slab can be
increased substantially by adding beams between coluinns. The cost of
construction, however, increases whilst it is much more time consuming and
expensive to construct. See figure 3.54.
1
Plane
Plaster
Screed
Reinforcing
Figure 3.53 Ordinary flat slab
Reinforced
concreteslab
Beam
Plaster
Screed
Reinforcing
Figure 3.54 Flat slab with beams
Reinforced
concrete
slab
1
Composite hallow block and concrete slab
Used in struciures which require a bigger span between columns. it has the
addeci advantage thai good sound isolation is obtained. The appearance of
the soffit is, however, unticy and can seldom be left without further finishing
being applied. This type of slab is an improvement on flat slabs but more
expensive. See figure 3.55.
Plaster
Hollow blocks
Concrete
Reinforcing
Figure 3.55 Composite hollow block and concrete slab
Goffer s/ap
Cofier slabs are used where large spans and heavy loading are required.
Conference rooms, spacious entrance foyers, parking garages and public
areas typically demand coffer slabs. Shuttering is inevitably of a high quality,
leaving a clean "egg box" effect on completion. Fibreglass shutiers are usually
L'seci and the underside of the completed slah (after stripping) is often left
as is or painted. See figure 3.55.
ou
Concrete
Coffer
Concrete
Figure 3.56 Coffer slab
1
1
Coffer
Reinforcing
6:0
Pre-stressed beam/słabs
Pre-stressed beam/slabs usually require heavy lifting equipment to place the
beams and is not as commonly used as the other types. The steel
reinforcement in the beams are stressed mechanically in the formwork before
the concrete is poured to form the beam. The beams are manufactured in a
factory and placed on site by crane. The main advantage of the system is
that less formwork is required as the beams have a bearing capacity of its
own. The hollow blocks rest on the beams requiring no or very little further
support before the concreie is poured. See figure 3.57. Pre-stressed slabs
can also be formed very rapidly by placing inanufactured concrete planks in
place as a slab. See figure 3.58.
Reinforcing
Concrete
Plaster
Pre-stressed beam
Figure 3.57 Pre-stressed beam/slabs
(E/2) Pre-stressed "plank" slabsScreed over top
OV:0:0:0:00:00.0
Pre-stressed concrete "planks" laid on wall or
ended in "in situ" concrete beams
I
Figure 3.58 Pre-stressed concrete "plank" slabs
Hollow block
0.00
Post-stressed concrete slabs
This is a sophisticated heavy load, long span slab which is costly. Certain
designs, however, dictate this as the most acceptable option. The slab (and
beam) construction is commenced as for an ordinary slab, but some of the
reinforcement is replaced with sleeves through which high tension cables are
placed. After a specified curing period for the slab, the cables are stressed
hydraulically to the tonnage required by the engineer. After tensioning the
sleeves are sometimes cement/sandi grouted with the end clamps or the
side of the slabs covered up. The soffit is formed by ordinary or smooſh
formwork. See Figure 3.59.
Tension cable sleave
Tensioning cables placed through sleeves and stressed
mechanically
Washer plateReinforcing
8 - Lock sleeve(light)
SECTION X-X
X
х
Washer plate
Lock sleeve
Figure 3.59 Post-stressed concrete slabs
0
Columns/walls
Columns/walls (shuttering) can be rade up in many shapes to satisfy the
requirements of the designer.
They are, however, normally square, rectangular or round, sometimes receiving
some structural and/or aesthetic capping. Formwork can be ordinary or
smooih in quality. See figure 3.60.
PLANS (ALTERNATIVES)
☺
Figure 3.60 Columns/walls
11
Second floor
First floor
3.6 BASEMENTS
Dry basements are ihe result of proper design and workmanship. In principle
there are iwo broaci possibilities to construci successful basements. Firstly, the
design can be to create an "urclerground tank” which is watertight, or secondiy
the approach can be to collect water via cavity walls and drains leading to a sump
from where it is puinped away. In certain instances these two principles can be
split by waterproofing the walls and draining the floor area. The expected water
pressure and volume will determine the most suitable option. See figures 3.51
io 3.65, which details proper construction methods.
if something does however go wrong, dampness, or even free water will be
experienced in basements.
D
E
☺
in
K
A Half-brick wall to protect waterproofing and receive finishes
B One-brick retaining wall
C Waterproofing (sealed tanking)
D Consolidated earth filling
E Broken stone 40 mm covered with fibreglass felt cloth
F Agricultural drain to sump if required
G Broken stone 40 mm covered with fibreglass felt cloth
H 100 mm concrete surface bed (1:3:6) floated smooth to receive waterproofing75 mm concrete surface
bed (1:3:6) to protect waterproofing and to receivefloor finish
J Concrete foundation (1:2:4)
K Floor finish
L Wall finish
M Natural ground level
Figure 3.61 Basement for single level
Figure 3.62 Basement for multi-levels
oe
VA
Alternative detail with
drain holes through slab
A Reinforced concrete slabs on columns or taken into retaining wall with waterchannel and seepage
holes (Alternative detail)
B Brick wall to receive finishes
C Void for surface water seepage
D Reinforced concrete retaining wall
E Water channel laid with falls to seepage openings
F Floor and ceiling finishes
G 100 mm concrete surface bed (1:3:6) laid on broken stone 40 mm
H Natural ground level
| Consolidated earth filling
J Fullbore water inlets
K Broken stone 38 mm around outlet covered in fibreglass felt cloth around pipe
[ 100 mm drain pipe to sump
M Agricultural drain to sump, 40 mm broken stone in fibreglass felt cloth around pipe
N Broken stone 40 mm
o Waterproofing membrane
P 75 mm concrete surface bed (1:3:6) to protect waterproofing and to receivefloor finish
Q Drain holes through slab built into D
Figure 3.63 Basement for multi-levels (continued)
А
-A
A Agricultural drains to fall to sump
B Retaining wall (type depending on site conditions)
C Sump to collect water
Figure 3.64 Plan of agricultural drain (not to scale)
А
In
A
SECTION A-A
E
A Water inlet from agricultural drain
B Submerged sump pump
C Water level depth control pump switch
D Water level
E Sump cover lid
Figure 3.65 Section of sump (not to scale)
PA
Disposal of
water
QUESTIONS FOR SELF-EVALUATION
1.
2.
3.
5.
6.
7.
8.
Discuss the procedure to ensure brickwork of a high quality.
Make ample use of sketches.
Draw a section through the internal wall of a simple structure
indicating strip footings, cavity wall and solid floor details.
Provide dimensions with complete descriptions of the elements
shown on the section.
Discuss five types of roof finishes using sketches with complete
descriptions.
iviake line sketches showing ten types of roof trusses.
Discuss the mixing and laying of concrete.
Discuss the funciion and use of reinforcing in concrete structures,
Use sketches to suppori the discussion.
Name and discuss five types of shuttering (formwork) for
reinforced concrete members, complimenting the discussion with
sketches.
Using sketches explain the construction inethod which you will
recommend for a inulti-level basement.
(25)
(25)
(50)
(30)
(15)
(15)
(25)
(35)
220
GEN
NOTES
BUILDING COMPONENTS
AND FINISHES
CONTENTS
LEARNING OBJECTIVES
4.1.1
4.1.2
4.1.3
4.1.4
4.1.5
4.2
4.2.1
4.2.2
4.2.3
4.3
4.3. j
4.3.2
4.3.3
4.3.4
4.4
4.4.1
4.4.2
4.4.3
4..4.4
4.5
4.5
4.6.1
4.6.2
WINDOWS AND DOORS
Window design and constructionTypes of windows
Methodis of window frame fixing
Door frames and linings
Doors
PLASTERING, SCREEDING AND TILING
Plastering
Screeding
Tiling
SHOPFITTING, JOINERY AND IRONMONGERY
Shopfitting
Joinery
Interior finishings
Ironmongery
ORDINARY CEILINGS
Gypsum board ceilings
Timber tongue-and-groove ceiling
General
Trapdoors
SUSPENDED CEILINGS
PARTITIONING
methods of consiruction
General
PAGE
... 151
151
151
151
152
155
156
159
15S
161
162
165
165
168
169
170
175
175
175
175
175
179
13:
18:
184
4.7
4.7.1
4.7.2
4.8
4.8.:
4.8.2
4.9
4.9. i
4.9.2
4.9.3
4.9.4
4.9.5
4.9.6
4.9.7
4.10
4.10. 1
4.10.2
4.10.3
4.10.4
4.10.5
4.10.6
4.10.7
4.10.8
4.10.9
GLASS AND GLAZING
Glass
Glazing
PAINTING AND DECORATING
Types of paint
Paperhanging
MEMBRANE WATERPROOFING
Definitions
General comments
Mastic asphalt roof coverings
Bituminous felt roof coverings
Elastomeric roof coverings
Expansion joints
Condensaiion and thermal insulation of concrete roofs
PAVING AND ROADS
Preparing the base
Tarred surfaces
Concrete paving blocks
Bonding
Prevention of puddle formation
Treatmeni of the ground
Construction oí edge restraints
Placing the sand bed
Laying of paving
QUESTIONS FOR SELF-EVALUATION
REFERENCES
184
184
187
191
192
20:
202
202
203
204
206
208
209
209
211
211
212
212
213
214
214
214
214
214
216
BUILDING COMPONENTS AND ! INISHES
LEARNING OBJECTIVES
The objectives are to introduce the student to the typical components and
iinishes found in building projects and the application thereof.
After completion oi this module the studeni should be able to inake iníormed
choices regarding building components and finishes.
4.1 WINDOWS AND DOORS
4.1.1 Window design and construction
Windows are openings in the wall of a building to admit light, or light and air. Their
form, number and size depend on the character of the building. In residences
where the inain object is to secure light and ventilation, some form of sash or
casement window is used.
4.1.2 Types of windows
Windows may be divided into iwo general types, namely: casement window frames with hinged
casements, and
double-hung sash frames with sliding sashes.
Casement windows
In casement window frames ühe casements (opening panels) are hung to the
frames by butts or special hinges, and may be top, bottom, side or centre
hung.
The casemenis may be so arranged that they open outwards or inwards,
but the latter method is seldom used owing to ihe Gifficulties encountered in
rendering the joints between the sash and frame waierproof and also because
of the possible danger of accident due io the obstruction caused by the sash
projecting into the room.
Steel and wood casemeni window fraines and sashes are used extensively
for all classes of building. The frames are built directly into the brickwork,
stone or concreie surrounding the window opening. Aluminiuin windows are
usually measured on site before manufaciuring to ensure thai a perfect fii is
obtained. Aluminiurn wirdows are ioo prone to darnage to be built in during
the initial construction phase.
The standard types and sizes of windows manufactured are numerous bui
they can be purpose made for specific applications.
For general building purposes, such as housing, it is economical to make use
of standard metal windows. These windows are available in a wide range of
patterns anci sizes and by using coupling members, two or more standard
windows can be combined to form a bigger unit.
Hot dip galvanising prevents deterioration or rusting of steel windows during
building operations and also gives protection in regions with high huinidity.
Galvanised steel windows are expensive and are therefore mainly used in
coastal areas io prevent corrosion. Figure 4.1 shows an example of a
standard steel window.
Side-hung casements have handles with two-point noses while top-hung
ventilators have peg stays with three stay positions.
Doubic-nung sash frames
For double-hung sash frames the sashes slide vertically, and are
counterbalanced by spring sash balances. The windows can be ieft open at
any height due to the sashes being balanced and are locked when closed
with a latch.
4.1.3 Methods of window frame fixing
Figure 4.1 shows the fixing of metal frames directly into brickwork and stone or
concrete. The factory fiited fixing lugs are built in as the work proceeds. The
lugs can be bent so as to coincide with the joints in the brickwork. To give a
weatherproof joint the space between the frame and brickwork is filled with mortar
and pointeci. The sketch aiso shows the various components of a steel window
frame and placement of the DPC below the winciow sill. If DPC is not inserted in
this position, dampness will enter through ihe sill and damage the wall firishes
below the internal sill.
Figure 4.2 shows a wooden window frame and opening casement in section at sill
level, and the window in elevation. Important features to note are the waterproofing
of the sill, consisting of a water bar and DPC below the external sill, and the homs
and fixing lugs to be built into the brickwork or other inasonry.
Side hung
casement
Internal sill
Figure 4.1 Steel window
Transom
iMullion
External sill
Reinforced brick lintol
DPC
Lug
Parlement hinge
(long hinge for
easy cleaning)
Glazing bar
Hopper window
K
.
H
DI
67
152
114
2
SECTION X-X
G
A Horns to be built into wall at four corners
† 911
B Water drip grooved in wood + 6 mm deep
C 9x9 mm glazing bar fixed with panel pins in 12 x 9 mm rebate
D 3 x 50 mm aluminium or brass weather bar
х
Х
ELEVATION
E Damp proof course152 x 152 x 19 mm grooved tiles bedded in 1:4 mortar, external sill
G Sheet glass fixed in frame with putty
H Internal sill
J
к
Metal lugs every four layers of brickwork, screwed to the wooden frame
and built into the wall for 300 mm
Side hung opening casement window
Wooden sill (part of window frame)
Notes
1. 12 mm spacing between opening sections and fixed sections
2. Wooden frames from Meranti or Sapele
3. Ironmongery aluminium or brass
Figure 4.2 Wooden window sill
А
4.1.4 Door frames and linings
Door frames
Door frames are built in as the erection of the structure proceeds. Provision
must be made in the frame to receive the door, ihat is to form a rebate against
which the door can shut.
This is achieved by solid rebating in wooden frames and by berding a rebate
into factory manufactured steel coor frames.
Examples of standard metal door frames are shown in figure 4.3.
Pressed steel door frame
Х
х
Transom
T-lugs three
per side
13 x 13
Stile ties
Three lugs
per side
Specified size
(110 or 220)
SECTION X-X
Figure 4.3 Standard metal door frames
44Steelframe
dimensions
Top vent
Pressed steel
transom
Door
Floor finish
Stile ties
AA
11:
PLANS]
Sidelight frames
Use is sometimes made of sidelight frames consisting of a door frame and
sidelighis (side windows) in a single unit, giving more lighting io ihe interior,
typically in foyers.
4.1.5 Doors
A door is basically framed or panelled work, but there is a great variety of forms,
arrangements of panels, and mouldings. The fact that it needs to open and
close means that it must be securely framed and glued. The swinging of a door
on its hinges puts greai strain on the joints in the stile on the hinge side, known
as the hanging stile. A sliding door hung from ihe top has its entire weight
suspended.
Sizes of door's
The width of a door is regulated by the purpose for which it is intended. In
public buildings provision is made for the free passage of several persons at
the same time, while in private houses and offices the standard size of
812 x 2 032 min is suitable for one person.
Construction of flush boarded doors
As a coor made of one wide board would shrink and warp, doors are made
up by putting several pieces together. These are held in place and stiffened
with stiles and ledges.
The best type of boarded door is one in which the framing is mortised and
ienoned together. Boarded coors are sometimes used as internal doors, and
a variety of effecis are produced by the finish on the door face which could
be natural wood, nardboard or patterned hardboard.
Figure 4.4 shows various commonly used types of boarded doors.
Ledged, braced and framed doors
Figure 4.5 shows the various doors discussed under this heading. The
ledged door is made up of three ledges usually from 125 to 175 mm wide
by about 25 or 32 mm thick according to the size of the door. To these are
nailed the tongued-and-grooved boards usually about i9 mm thick. The upper
edges of the ledges are bevelled when the door is to be used externally, so
preventing water lodging on the rails. The door is hung to a frame screwed
through the ledges.
The ledged and braced door is similar to the ledgeci door, except that it is
strengthened by braces. The hinges should be fastened to the side of the
door from which the braces rise, then any tendency for the door to drop at
its other side will be resisied by the braces. The boards and the top edges
of the braces and ledges are bevelled.
In the framed ledged and braces door the top rail and stiles are of equal
thickness, usually 45 mm and the lock (or middle) bottom rail and the
braces are less than the thickness of the stiles by the thickness of the
tongued-and-grooved boards. The stiles and rails are framed together with
mortise-and-tenon joinis.
HOLLOW CORE FLUSH DOOR
1
1
Ledge
Stile
Paper core
Lock block
30 x 114x710
Hinge block
30 x 68 x 255
Facing
SEMI-SOLID FLUSH DOORLedge
30 x120
Stile
30 x 114
Core strips
Facing
Figure 4.4 Boarded doors
BALANCED FLUSH DOOR
SOLID FLUSH DOOR
Ledge and stile
30 x 75
Paper core
Lock block
30 x 114x710
Facing
Ledge and stile
30 x 114
Laminated wood
core
Facing
LEDGED BATTEN DOOR
in
Top ledge
Tongued-andgrooved planking
Centre ledge
Bottom ledge
FRAMED, LEDGE & BRACED
BATTEN DOOR
PANEL DOOR
Top ledge
Brace
Centre ledge
Stile
Bottom ledge
Top ledge
Stile
251
Glazing bead
Glazing bar
Bottom ledge
LEDGE & BRACED BATTEN DOOR
Top ledge
Brace
Centre ledge
Bottom ledge
251 25
30
FRAMED BATTEN DOOR WITH BACKING
Top ledge
50 x 100
Intermediate ledge
19 x 152
Stile
50 x 100
Bottom ledge
25 x 220
FLUSH DOOR
Top ledge with
ventilation
openings
Core filling
Lock blockPlywood or
hardboard
Edge strip
Figure 4.5 Ledged, braced and framed doors
Lock block
XXM
In panelled doors ihe proportions and design of ihe panels vary considerably.
Panelled doors are suitable for internal and external use, but when they are
used externally it is necessary to provide against effects likely to be caused
by exposure to the weaiher. Exiernal coors usually have iheir panels of the
same material as the framework of the door and hardwood is commonly used.
4.2 PLASTERING, SCREEDING AND TILING
4.2.1 Plastering
Sand
The sanci for inaking plaster should be of medium fineness and free from
loamy matter or clay. Before it is used, all sand should be well screened
(sieved) to remove coarse particles.
The best plaster is made of sand thai is screened, washed and dried. In
most cases, the sand is merely screened river or pit sand. The river sand,
through possibly cleaner, does noî make such strong mortar as does pit sandt,
because the grains are water-wom sinooth and rounded, not angular and
sharp. Sand inust be washed to get rid of loamy matter and clay if necessary.
Sea sand should not be used unless freed from salt.
Ordinary plaster
Plaster is usually applied in a single 1:5 (cement: sand) coat although two
coais are used where a very smooth finish is required. The second coat is
a fine density gypsum plaster product.
Textured finish
To provide a textured finish the surface is scored with a tool to provide the
desired effect while the surface is only partially hardened.
Rough-Gast
Rough-cast is obtained by mixing 6 parts coarse river sand with 1 pari cement.
Water is added to form a slurry and the mix is dashed on to the wall or ceiling
with a hand-operated machine.
Pebble dash
This finish is obtaineci by dashing dry coarse grit, gravel or sione-chippings
on to a first coat of plaster while it is wet, so that the material becomes
embedded in it. Patented products are available where the pebble is dashed
onto a synihetic glue which has been applied to a dry plastered surface.
Labour only ftems
Certain plastering details are known as “labour only items” because they
require no further material. Figure 4.6 shows various of these details.
FLUSH JOINT
DPC
DPC
FAIR EDGE AND ARRIS
HALF V-JOINT
V-JOINT
Figure 4.6 Labour only items in plaster work
DPC
DPC
ARRISED ANGLE
UD
V
FAIR EDGE
BUILDING COMPONENT'S AND FINISHES
SLIGHTLY ROUNDED ANGLE
V-JOINTTROWEL-CUT JOINT
Figure 4.6 Labour only items in plaster work (continued)
4.2.2 Screeding
The screeding of iloors is clone to provide a smooth layer (also called topping)
on concrete surſace beds or slabs to receive floor finishes. In the case of ihin
floor coverings, such as vinyl asbestos tiles and other plastic sheetings, the screed
needs to be particularly smooth to ensure that irregularities are not shown in the
final finish.
Preparation of the base
It is very important that the concrete, before receiving a screed, is thoroughly
cleaned to ensure adhesion. This is done by chipping off all loose particles
and to expose some aggregate on the surface of the concrete. The surface
thus prepared is then washed clean with water. The area to receive the
screed is grouied by vigorously brushing a 1:4 cement: sand mixture onto it.
The surplus grout is brushed off and the screed laid while the grout is still
visibly wet.
Scrosd laying
The screeding is done by spreadirg a 20 to 40 mm ihick layer of damp inortar,
containing sand and coarser (5 mm) aggregates. The 1:5 mixture is spread
over the prepared area, roughly ievelled and then rammed for consolidation.
After working it off to the required level, it is smoothed off by a steel trowel,
spreading a 1:4 very workable grout over the area, which provides a smooth
final surface.
Grano
To provide a floor with a natural cement or coloured surface, not to receive
a further floor finish, a screed called "grano" (granolithic finish) is provided.
In this instance the aggregates used have high abrasive resistance and the
mixing proportion increased to 1:3. Grano should be laid in blocks which
are cui loose from each other by a trowel whilst still wet, not more than 9 m2
each.
4.2.3 Tiling
Tiles are clay products which are burnt in a kiln to ensure a hard durable product.
Natural clay tiles, commonly known as quarry tiles are normally 15 to 40 icin thick
and 150 x 150 mm to 300 x 300 mm in size.
Glazed tiles are thinner and manuiactured from a finer clay. Patterns, colours
and pictures can be applied before glazing. Thicknesses vary from 6 to 20 inm,
with ihe most commonly used size being 150 x 150 mm. iviany other sizes are
available, particularly in the case of imported tiles. The term glazed tiles are often
used when referring to wall tiles. Ceramic tiles are harder glazed tiles suitable for
iloors and walls, as are quarry tiles.
‫܀‬
Fixing
BUILDING COMPONENTS AND FINSHES
Tiles are placed in two ways: Thick bed: Floor tiles are laid in grout directly onto a damp screed which
has been prepared as described under screeding.
Tiles can be laid in an adhesive which is applied to the walls and floors
with a grooved trowel after the plastering and screeding have dried. This
is the most common practice which ensures a high quality finish.
Grouting jointing)
Grouting is done after the cement or adhesive has set. A patent filler is
usually used for grouting of the joints between tiles. The grout, in a paste
form (powder mixed with water), is worked into the joints, allowed to dry and
then smoothed off or pointed to the desired effeci.
General
Figure 4.7 shows details of various nosings and corners in tiling work.
Figure 4.8 indicaies the precautions to be taken when tiling over an area
where differential movement between different backing materials is expected.
Round edge tile
Cushion edge tile
Attached angle tile
Glazed edge tile
Mitred corner
Exposed unglazed
edge (common in
practice, not neat)
Glazing
Figure 4.7 Tile corner details
Horizontal internal sill
with round edge
Sloping internal sild
with round edge
Glazed
bulinose
// / / / /
Internal
corner detail
//
Concrete
Plaster
Concrete
Plaster
Tiles
Tiles
Brickwork
2.
Joint filled with elasto material (silicone)
Gauze
Brickwork
02
Brickwork
Tile grout
(solid Joint)
Figure 4.8 Movement and solid joints in tiling
Adhesive
onto
plaster
Adhesive
onto
plaster
Plaster
Adhesive
onto plaster
Tile
4.3 SHOPFITTING, JOINERY AND IRONMONGERY
4.3.1 Shopfitting
Shopfičting deals with interior furniture and fittings of a building which are
manufactured, installed and fixed in position after ihe structural framework and
most of the finishes have been completed.
These items are mainly pre-manufactured and are of a very high quality finish.
Corporate image is very important and shopfitting is often the vehicle used to
inake a visible statement.
Office shoplifting
A wide range of office furniture is available - from mass produced chairs,
cesks and cupboards to pre manufactured units delivered in “kit” form to be
assembled and fixed in each office. Reception counters, office furniture and
boardroom furniture and fittings are some of the more expensive items
designed to provide a specific corporate image.
Residential shoplifting
In the residential market, “shopfitting" mainly involves kitchen cupboards,
bathroom furniture, bedroom cupboards and entertainment area furniture.
All these items are normally pre-manufactured and are installed after all wei
trades have been completed and the building is weatherproof.
Kitchen Gupboards
Manufacturers generally use standardised catalogues in which the units
are classified as base (floor) or wall units. A wide range of items such
as wine racks, oven cupboards, pot-drawers, etc. are available. A range
of typical base and wall units with the relevant dimensions are shown in
figure 4.9.
A wide range of materials are used; from natural indigenous or imported
wood to different inelamine (plastic) finishes.
Built-in cupboards
As for kiichen cupboards, built-in cupboards have developed to a
standardised item. All the parts or the cupboard are pre-manuíactured
and supplied in kit form, whereafter the different units are assembled
on site to obtain a final product. It is important that measurements for
manufacturing are taken only when the building is ready to receive the
cupboards to ensure proper fitting in the allowed space.
Bathroom cupboards have also become a sianciarci pre-manufactured
item which is bought oíf the shelve.
SASE UNITS
Lengin
mm
Length
inm
Length
mm
300
Base unit
3 Drawers
400
Base unit
Full height
door
600
Base/sink/
hob unit
Full helght
door
Figure 4.9 Base and wall kitchen cupboards
11
300
Base unit
1 Drawer
500
600
Base unit
Full height
door
Base/hob
unit
1 Drawer
400
500
Base unit
Full height
door
Base unit
1 Drawer
600
Base/sink/
hob unit
1 Dummy
drawer
Base unit
1 Drawer
400
500
Base unit
3 Drawers
600
.€
Base unit
3 Drawers
CORNER WALL UNITS
WALL UNITS
Length 600 mm 740 mm 900 mmhigh high high
Length 600 mm 740 mm 900 mm
mm high high high
Length 600 mm 740 mm 900 mm
mm high high high
mm
625
300
633
733
933
800
683
783
983
[H
600
Unit
625
663E33 763E33963E33
300 300
Return Door
Figure 4.9 Base and wall kitchen cupboards (continued)
DIAGONAL CORNER WALL UNIUS
101
400
63
743
943
1 000
6 103
9 103
7 103
Length 600 mm 740 mm 900 mm
inm high high ilgh
625
663EDW|763EDW 963EDW
LI
500
653
753
953
1 200
6123
7 123
9 123
600
663
763
963
Gommercial shopfitting
The main areas of commercial shopfitting are counters, reception areas and
display areas in shops, banks and other commercial buildings, where trading
with the public takes place. There is less standardisation in this area.
Corporate image requirements often lead to standardisation within a specific
organisation regarding quality, design, etc.
Shelving for merchandise in shops involves pre-manufactured standardised
systems that can be bought in different heights, lengths and widths.
In restaurants shopfitting consists mainly of purpose-made counters and
decorative units. Furniture like tables and chairs are pre-manufactured and
installed either fixed or loose.
Traditional joinery shops are no longer playing a major role in shopfitting as
inost of the items are produced in highly sophisticated factories and supplied
in kit form, ready for site installation.
Shopfronts
Shopfronts consist mainly of aluminium frames fitted with safety glass. When
required as part of a marketing strategy, other materials such as wood are
used.
Shopfronts are part of the building and are installed during construction. The
owner of a building may not be willing to change shopfronts each time tenants
change, and such changes are normally for the cost of the ienant.
4.3.2 Joinery
Joinery guidelines
Joinery, as distinguished from carpentry, deals with those interior and exierior
ümber elements of a building that are fixed in position, usually after the wet
trades have been completed. In joinery the chief requirements are: quality tiinber
close-fitting joints
accurate workmanshipsmooth-finished surfaces
As good appearance is of great importance, joinery surfaces generally have
a clean finish and are prepared in such a manner that they form a good base
for painting or staining and polishing. Wherever possible the work should be
arranged so that no end grain is visible on ihe surface.
Timber is called "sawed" when referring to it in the sawn state from a log.
Allowance must be made in the sizes for p! aning, being 3 mm for each planed
(wrought) face of a member:
For example, the finished size of a 100 x 75 mm member wirich is planed
on all four faces, is 94 x 69 mm. For this reason it is common io quote on
joinery sizes as the “sawed" size to be planed all round (PAR).
Machinery and craftsmanship
The progress achieved in the design and operation of woodworking machinery
(often computer controlled processes) and the standardisation of many joinery
components, permits work which was previously produced by hand methods
to be machined with speed and precision. Examples of this are mass-produced
standard doors and window frames, where the only handwork necessary is
the assembly of the members after they have been machined. However,
"purpose-made" joinery and certain high-class individual handwork by a joiner,
give opportunities for the exercise of craftsmanship and skill.
Provision for expansion and contraction
All timber is subjected to changes in size due to climatic conditions. Joinery
work, therefore, should be fixed so that it is free to expand and contract
without damaging the product or becoming unsightly.
This is accomplished by securing one edge only when fixing, permitting the
other to rest in a grove in such a position that it may contract or expand.
When both edges are secured, shrinkage will cause the timber to split, and
when it swells, it will either bulge or push out the securing nails or screws.
Narrow boards are preferable to wide ones, as the swelling and shrinking
are distribuied over a larger number of joints and are less noticeable. After
the members have been prepared in the workshop, care in stacking prior to
use on the site is essential to prohibit warping or other damage.
A thorough knowledge of the properties of various types of timber is
important in joinery.
4.3.3 Interior finishings
Typical interior joinery finishings which are applied are the following:
Architraves
Architraves provide a lining to openings and can be secured as íollows: Where the architrave is of
softwood and to be painied, it can be nailed
or screwed to timber runners (grounds) which have been fixed to the
plaster surface.
Hardwood architraves to be varnished or polished can be fixed by
screwing from the face, the holes being filled in with timber pellets glued
with their grain in the same direction as that of the architrave.
Fiardwood architraves can be secured by secret slot screwing.
Skirtings
A skirting is the horizontal timber sirip placed at floor level to cover the joint
between the wall and the flooring. For neatness and convenience in fixing,
skirtings should not be unduly large and should preferably be of a simple
profile. However, large profiled skirting which has been fixed by a good
craftsman makes a superb high class statement in formal areas.
4.3.4 Ironmongery
‫܀‬
Door boits
A large variety of door bolts is available on the market. These bolts are made
in many sizes in steel, aluminium, brass anci bronze and may be procured in
a variety of finishes. Figure 4.10 shows several types of door bolts.
Necked barrel bolt
e
Flush bolt
Barrel bolt
14
Mortic bolt
Figure 4.10 Door bolts
Indicator bolt
Door chain
Keep
Cupboard bolt
Door locks
There is a great variety of types and quality of door locks. Generally tirey
are classified as rim locks and mortise locks. Rim locks are secured to the
surface of the door and exposed to view, mortise locks are let into a mortise
cut into the edge of the stile and only the face of the lock is visible on the
edge of the door.
Rim locks
Rim locks are generally used due to their low cost and because they are
easily applied to the doors. They merely need screwing to the surface
of ihe door and frame.
Rim locks may be obtained in various shapes and sizes. A typical
example of a rim lock is sirown in figure 4.11. The keyhole may be
double ended which allows the key to be used from both sides. When
the keyhole is single ended, the lock is provided with a hand knob for
unlocking from the inside.
Rim Lock
Figure 4.11 Rim lock
Mortise locks
ivortise locks are available in 2, 3 and 4-lever locks, indicating a rising
quality of mechanism for greater security. It is more time consuming to
fit mortise locks, making it more expensive than rim locks. Due to
functionality, however, it is ühe most used lock (see figure 4.12). Moriise
locks are also available with a cylinder which receives the lock key. The
cylinder fits into the lock mechanisin, operates with a small key and is
substantially more secure than an ordinary keyed mortise lock.
BUILDING PRACTICE - VOI. UME 1
Mortise lever lock
Striking plate fixed to frame
Cylinder lock
Knob set
Figure 4.12 Mortise locks
Mortise lever lock handle set
9.
Cylinder lock
Pins
Rotatingplug
Cylinder lock showing pin tumbler mechanism
General ironmongery
The following general ironmongery which is commonly used is demonstrated
in the following sketches: Escuicheons: figure 4.13
Barrel bolts: figure 4.14
Door ironmongery: figure 4.15
Sundry ironmongery: figure 4.16
Figure 4.13 Escutcheons
ថា
DO
TOWER BOLT
Bolt
PADLOCK BARREL BOLT
Barrel
Hoool
Barrel
Figure 4.14 Barrel bolts
HINGES
03
Butt hinge
TO
Dubl
hinge2
Parliament hinge7
0
O
Tee hinge1]
butt
Vasnered butt
Flap hinge8
3
Piano hinge12
Bolt
D
BARREL BOLT
Ballbearing
butt4
O
BoltBarrel
Plate fixed to door
‫ات‬
Hamborg
hinge5
StraightDovetail
9A9B
Counter flap hinges
Figure 4.15 Door ironmongery
Centre hinge13
on
Rising butt6
30
Strap hinge10
o
Flush hinge Offset hinge
1415
DOOR CLOSER
HASPS AND STAPLES
DOOR STOPS
Figure 4.15 Door ironmongery (continued)
10
Figure 4.16 Sundry ironmongery
4.4 ORDINARY CEILINGS
4.4.1 Gypsum board ceilings
Ceilings are usually cone in gypsum board in small buildings. The gypsum board
consists of two sheets of thick paper with gypsum pressed in between to form a
composite board.
These sheets are naileci to ceiling brandering with clout head nails (flat headed
nails). The joints are held together between the boards with a metal H-section or
the joint is covered with a ílat wood strip or gypsum board strip. See figure 4.17.
The joints can also be closed by using boards with bevelled edges. These edges
are butted together after which a jute or metai scrim is stapled to the boards in
the recessed edges and then plastered over with a skim coat of gypsum plaster
which fills the recessed area. On completion the ceiling displays a smooth
underside with concealed joints. See figure 4.18.
4.4.2 Timber tongue-and-groove ceiling
Timber ceilings are formed by using tongue-and-groove timber strips such as pine,
meranti, saligna, etc.
The timber is secretly nailed to the brandering through the back lip of the groove
which is then covered with the tongue of the next strip, which is fitted into the
groove. It is important not to fit the timber strips too tightly as this will cause
buckling of the ceiling with moisture increase in the air. See figure 4.19.
4.4.3 General
Ceilings are finished at ihe walls by leaving a gap between the boards/timber and
the walls for expansion and movement, which is covered with a cornice. In the
case of gypsum ceilings the cornice is usually made of profiled paper board with
gypsum in between. This cornice is butt jointed in length, with the joint smoothed
off with gypsum plaster or a pre-paint filler. See figure 4.20 showing a general
ceiling section.
Timber ceilings and sometimes gypsum ceilings, are finished against the walls
with a profiled timber quarter round or with a 40 x 20 mm rectangular timber strip.
4.4.4 Trapdoors
Airapdoor is insialled to provide access through the ceiling to every separate
void above the ceiling with at least one installed near the geyser or oiher services
above the ceiling. The minimum size for a trapdoor is 600 x 600 mm and it is
consiructed on site as shown in figure 4.21. Figure 4.22 shows a factory
manufactured ceiling trapdoor.
DETAIL "A"
38 x 38 mmbrandering
6 mm gypsum celling board
38 x 38 mm
brandering
Tie beam
6 mm gypsum
ceiling board
Pressed metal H-section
ceiling joint strip
Tie beam
6 mm gypsum ceiling board
6 mm x 38 mm wood or gypsum
celling board joint cover strip
Figure 4.17 Ceiling joint finishing
Gypsum plaster
over entire
ceiling area
38x38 mm brandering
Fibreglass plaster
gauze strip stapled
to ceiling board
Tie beam
12 mm gypsum ceiling board
Tie beam
38 x 38 mm brandering
12 mm gypsum ceiling board
with recessed sides
Fibreglass plaster gauze strip
stapled to ceiling board and
recess only plastered with
gypsum plaster
Figure 4.18 Gypsum ceiling with concealed plaster joints
E
38 x 38 mm
brandering
DETAIL "A"
Tongue-and-groove ceiling planking
38 x 38 mm
brandering
Figure 4.19 Timber tongue-and-groove ceilings
А
с
38 x 38 mm ceiling battens nailed to tie beams at 450 mm centres
(celling boards 900 mm wide)
Ceiling boards consisting of one of the following:
1. 6 mm thick gypsum board
2. 6 mm thick hardboard
3. 12 mm thick piastered gypsum board
4. 12 mm thick softboard
5. 6mm thick cement fibre board
6. 13 mm tongue-and-groove planking
AAN
Concealed
nailing
38 mm wood (meranti) quaterround fixed alternatively to wall and ceiling battens
75 mm gypsum board cornice fixed at 300 mm centres alteratively to wall and
ceiling battens
Coverstrip 6 x 38 mm of wood or gypsum board on joints between ceiling boards.
Wire (or metal strip) roof tie
Figure 4.20 General ceiling section
PLAN
SECTION A-A
А
с
D
E
F.
G
G
IN
D
ET
‫ب اه‬
G
Ceiling battens
Ceiling board
600 x 600 mm opening for trapdoor in ceiling
38 x 38 mm ceiling battens around opening in ceiling
38 x 38 mm batten frame with ceiling board fixed to it
10 x 50 mm plained and rounded angle planks. Mitred at ends to form a frame and
screwed to D through B so that frame projects 25 mm into opening to receive trapdoor
Tle beam
Figure 4.21 Site manufactured ceiling trapdoor
PLAN
À
SECTION A-A
А
с
D
E
G
E
Ceiling battens
Ceiling board
600 x 600 mm opening for trapdoor in ceiling
38 x 38 mm ceiling battens around opening in ceiling
38 x 38 mm batten frame with ceiling board fixed to it
Patented steel trapdoor
Tie beam
E
Pivot point
Figure 4.22 Factory manufactured ceiling trapdoor
А
4.5 SUSPENDED CEILINGS
Suspended ceilings are usually used in non-residential buildings such as office
blocks and shopping centres where it is imporiant to form a ceiling void io
accommodate air-conditioning ciucis, mechanical, electrical, water, sewerage and
other services.
Suspended ceilings are either demountable or fixed. Demountable ceiling panels
are mounted in suspended T-sections which are usually powder coated (paintec)
and visible. Fixed panels are slid into T-sections which are not visible, resulting
in the entire ceiling forming a continuous boarded effect.
Suspended ceilings are of modular design which ties in with air-conditioning,
electrical and partitioning systems. Fixed panels should only be considered where
no services are concealed in the ceiling void. A further disadvantage of fixed
panels is that if one panel is damaged, a large portion of ceiling has to be stripped
to do remedial work.
A variety of ceiling board types are available in orcier to achieve the desired
acoustic and aesthetic effect.
Typical sections demonsirating suspended ceiling systems are shown in figure 4.23.
Electrical
services
Concrete floor slab
Air-conditioning ducting
DETAILS "A"and "B"
Suspended hanger brackets
Suspended
ceiling
hanging
bracket
O
Water
Wall
Sewerage
Cross T-section laid loose
between boards
Fixed with power
nails or screws
Removeable celling boards
Main
T-section
ALTERNATIVE T-SECTIONS
Figure 4.23 Suspended ceiling systems
DETAIL "B"
SECTION
Underside
of concrete
slab or other
roofing
Fixed ceilingpanels
4.6 PARTITIONING
Partitioning is lised io divide space within a building into a varieiy of room/office
sizes. With the ever changing needs in buildings, the use to which space within
a building is put changes during the lifetime of the building. It is thus more
economical to use cerrountable partition walls. The advantage of future flexibility
musi, however, be set against the increased initial cost to obtain demountability.
Demountable partitions and suspended ceilings are norinally used simultaneously.
4.6.1 Methods of construction
There are numerous partition systems available, mary having patented fixing
devices. Partitioning consists of one of the following systems:
frame and panel system
Gypsum plasterboard drywalling
Frame and panel system
Rolled galvanised steel sections or aluminium extrusions are used to form a
frame into which panels of a variety of materials are fixed. iMore complex
panel construction may incorporate a single or double skin of pressed steel
or aluminium sheets. This type of double skin panel may be fitted with glass
fibre or mineral wool to improve sound isolation. Most proprietary systems
offer a number of permutations of glazed to solid arrangements and are
available as single or double glazed units. The glass is usually secured with
a gasket type fixing. Figure 4.24 shows a iypical frame and panel system.
Solid
panel
51 mm
solid panel
KEY ELEVATION
Ceiling
51 mm
aluminium or
PVC cornice trim
76 mm
aluminium or
PVC skirting
Floor
Glazing
Solid
panel
Junction
component
Glazed
panel
Solid
paņel
Door
frameDoor
ISOMETRIC
6 mm foam rubber
WWW017resilient seal
Aluminium
junction component
Spring
clip fixing
Wiring
ducts
Springclip fixing
6 mm foam
rubber seal
Aluminium
door frame
Foam rubber
draught seal
Semi-solid
flush door
Timber infill
A simple concealed fixing frame and panel system
©
Figure 4.24 Frame and panel partitioning system
Gypsum plasterboard drywaliing
Timber stud framing
Aluminium
junction component
4 mm glass
PVC
glazing bead
Sheets of gypsum board are attached to vertical timber studs set at
regular intervals. Timber sections are norinally 38 to 50 mm thick and
75 io 100 mm wide. A horizontal timber support is generally positioned
halfway beiween floor and ceiling for added rigidity. The joints are then
iaped and felted, sanded flush and the walls painted to give a monolithic
finish.
Motal stud trening
The frame usually consists of 0,8 mm thick (22 gauge) galvanised steel
channels approximately 65 mm wide, secured to the floor and ceiling timber or
concrete slab, into which galvanised steel studs at 600 mm centres (maximum),
are inserted by twisting them into position. The flanges of studs and channels
are crimpece together at floor and ceiling. Double studs may be provided on
each side of door and window openings with a track channel lintel above.
Gypsum boards are attached to the studs and framework. A variety of finishes, like
paint or vinyl cladding (wall paper), is used to provide the desired finish. See
figure 4.25.
Gap for
movement
0,8 mm thick studs
at 600 mm centres
Track channel
shot or nailed to
concrete floor with
high tensile nails
Plastic skirting fixed
with adhesive
Figure 4.25 Gypsum board partitioning system
Aluminium
cornice
Sealer compound
if required
Track channel shot or
nailed to concrete
ceiling with high
tensile steel nails
Glass-fibre insulation
can be installed in
cavity
12.7 mm gypsum board
Timber skirting
fixed to studs
Post and panel system
This system has a joint between ihe edges of the panels and posis. The
panels and posts are retained at floor and ceiling level by means of timber.
plates, galvanised steel studs, or aluminium sections. The panels consisi of
storey height sheets of gypsum board, or other suitable material.
4.6.2 General
iviany systems have special details such as adjustable floor fixing and levelling
supports, telescopic transom rails or removable pilasters to service ducts. In
most of the systems the studs and other sections are manufactured from
galvanised steel, with the studs having holes punched through the web-section
to accommodate services.
4.7 GLASS AND GLAZING
4.7.1 Glass
Glass is composed of three chemical constituents: silica, soda and lime. These
are mixed in varying proportions to suit the requirements of each case. It could
also be mixed with an additional element to vary the colour or degree of
transparency of the finished produci.
Three general varieties of glass are used in ordinary buildings: sheet glass,
float glass and plate glass. Each is used under certain conditions limited by the
character of the work and the properties of the glass.
Giear sheet glass
The raw materials from which sheet glass is made are melted and refined in
a tank furnace at a temperature of about 1 400 °C.
In a continuous process, the glass passes from a melting furnace to a
reheating chamber, from which the molten glass is drawn upwards from the
tank by rollers. These rollers control the width of the sheet of glass, whicii
passes between them in the form of a broad ribbon. As it passes upwards
its temperature decreases ai a rate which is careíully controlled. The
temperature of the last pair of rollers is kepi at 125 °C. The rate at which
the glass is drawn upwards depends on the thickness required.
After passing through the rollers, the glass enters the cutting room wiere it
is cut into standard sizes. The two surfaces of drawn sheet glass are never
perfectly flat and parallel, so there is always some distortion oí vision.
Sheet glass is the most commonly used glass for general glazing, and is
available in various thicknesses. When specifying sheet glass, it is described
by the thickness of the glass.
The available thicknesses are 2, 3, 4, 5, 5.5, and 6 mm, bui owing to the
lack of parallelism of the glass surfaces these values sirould be regarded as
nominal, with some degree of tolerance, either positive or negative, being
permitted.
Three qualities of sheet glass are obtainable:
ordinary glazing quality (OQ), suitable for general glazing;
selected glazing quality (SQ), used for glazing work needing a sheet
glass superior to the ordinary glazing quality;
special selecteci quality (SSQ), used for high grade work.
Polished plato glass
The melted glass passes through casting rollers in a continuous ribbon
before it is cooled. It ihen passes through a long horizontal heated tunnel
with carefully controlled temperatures. While passing through the tunnel,
the class ribbon is supported on steet rollers. It passes through a machine
which grinds and polishes the rough surfaces, making them perfectly parallel.
It is thicker than sheet glass but until polished, lacks the transparency of
sheet glass. It is completely free from imperfections and does not distort or
disform objects as does sheet glass. Plate glass is norinally used in large
panes, such as shopfronts as it permits undistorted viewing.
Rolled glass
The initial steps in the production of rolled glass are much the same as in
the manufacture of plate glass. The glass is melted in a tank furnace, then
passes to one of several types of machines, ihe actual type depending upon
the particular form of rolled glass required. The essential common feature
of these machines is a pair of steel rollers, both of which may be plain as in
the manufacture of rough cast glass, or one (usually the bottom roller) may
have a pattern cut into fis surface in order to imprini a pattern onto the glass.
The molten glass is forced between these rollers and einerges as a ribbon
which is patterned before being cut to lengths.
The principle varieties of rolled glass are: rough cast, plain rolled, figured
rolled, cathedral rolled and wired glass. Special glasses, such as prismatic
glass, are also forms of rolled glass.
Rough cast glass is a rolled glass in which boih su faces have an irregular
texture, one surface being smoother than the other.
Plain rolled glass is transluceni roiled glass. One surface bears a pattern of
narrow parallel ribs, the other is flat. The parallel ribs diffuse the light and
reduce direct glare from the sun.
Figured rolled and cathedral glasses are rolled glasses wilich may be tinted
or untinied. One surface of cathedral glass has a definite texture, whereas
one surface of figured rolled has a pattern. According to the configuration
of the pattern or texture, vision can be obscured to any desired extent.
Float glass
The float process is very simple in principle. The glass obtains its lustrous
finish and perfect flatness by floating the molten glass on a bath of molten
tin in a chemically-controlled atmosphere. The ribbon of "floated" glass is
then cooled, while still advancing on the surface of the tin, until the glass is
hard (cold) enough to be taken out of the bath without the rollers marking the
surface. This process is more efficient than that for polished plate glass.
Because the glass is smooth and the surface absolutely parallel, grinding and
polishing are not necessary.
Hired glass
Wired glass is rolled glass in which wire is embedded during rolling. It can be
obtained either in the rough-cast form or with a polished finish. The roughcast form is used where clear
vision is undesirable. The polished form
provides the clear vision characteristics of polished plate glass. The wire
mesh is typically a Georgian welded mesh, 25 x 25 mm square.
The wire is embedded in the molten glass at a temperature which ensures
cohesion between the mesh and the glass, and the two materials become
one.
Consequently, if the glass is broken by shock, intense heat, or from some
other cause, the pane as a whole reinains intact and ii does not shatter like
float glass.
Wired glass is practically burglar and impact-proof and when glazed in
metallic frames, forms an efficient fire-retardant window.
Toughened glass
Armourplato glass
Orcinary float or polished plate glass is made into a toughened glass
and sold urder ihe trade name Armourplate. A process of heating and
suciden cooling is used which produces a glass of greatly increased
sirength, much more resistant to impact and sudden and large iemperature
changes. Any drilling of holes on this and other toughened glass must
be done before ihe toughening process because it cannot be done
afterwards. Armourplate glass and other toughened glasses are used
in building work for shopfronts and frameless glass doors.
Armourlight glass
This trade name is applied to certain shaped and moulded glasses when
ioughened. These glasses may be used for roof and pavement lenses
as well as for glass bricks in walling where resistance to impact and
severe thermal conditions are required. Armourlight products are specially
designed for translucent constructions. They have an exceedingly high
resistance to mechanical loads and severe thermal conditions.
Other toughened glasses
The toughening process can be applied to several other flat glasses.
The extent to winich the strength of the glass and its resistance to sudden
temperature changes can be increased will depend upon the type of
glass.
4.7.2 Glazing
Fixing with putty
Glazing into wood
The simplest form of glazing is into rebates formed in wood frames, the
glass being held in position by means of putty - a composition of raw
linseed oil and whiting, ground and keaded into a stiff paste resembling
cough. The glass should be slightly smaller in size than the extreme
distances between the rebates, in order that the intervening bed of putty
may prevent the glass from coming into contact with the frame, thus
preventing fracture owing to concussion or expansion.
The woodwork should first be primed with a woodsealer so that the putty
will adhere. Failure to prime the woodwork will result in rapid absorption
of the oil in the putty, making the putiy britile, which in turn causes it to
fall out.
An example of putty glazing into wood is shown in figure 4.26. After the
primer is dry, a layer of putiy is spread over the rebate into which the
glass is firmly becided.
Back
putty
Window glass pane
Front putty (outside)
Frame
Figure 4.26 Fixing of glass with putty into a wooden frame
Fixing with beads
In high quality work timber beads known as glazing beads are used in
lieu of putty only.
The glass is back-puttied before the beads are fixed with screws or panel
pins so thai it may be removed in the case of glass breakage. Figure 4.27
shows the usual method of fixing with wood beads.
Panel pins or screws
24
Beading (outside)
Window glass pane
Back putty
Frame
Figure 4.27 Fixing of glass with glazing beads into awooden frame
Glazing into metal with glazing beads is similar to thai for wood, except
that in all cases the beads must be screwed. This is accomplished by the
use of tapped (threadieci) holes, previously prepared in the inetal members
to receive threaded screws, the wood beads being drilled accordingly.
The wood beads can also be replaced with steel or aluminium beads.
In the latter instance rolled aluminium channels are sometimes used.
Glazing into metal
This is performed similarly to glazing into wood. Various proprietary
mastics and putties for glazing into metal are available. Back and front
putties are required, the metal first being coated with a metal primer.
Figure 4.28 shows a iypical detail.
Exterior plaster
Front window putty(outside)
Back window putty
Opening window
casement
47
External window sill
1.'
2
Lug
Interior plaster
Fixed profile
Window pane in
putty
Fixed profile
Internal window sill
Damp-proof course
Figure 4.28 Fixing of glass with putty into a steel frame
Patent glazing
Putty is unsuitable for glazing large panes of glass due to excessive expansion
and contraction of the glass and frames. Special forms of glazing, which
dispense with the use of putiy, have consequently been devised.
The Lise of patenied aluminiuin frames and glazing bars has proved very
successful for large windows, giving lightness in weight and a high degree
of resistance to corrosion, requiring no maintenance.
Figure 4.29 shows typical details.
2400
DETAIL A
Mastic
bed
600 600
KEY ELEVATION
25
600
C/S of bars
19 mm
|3
25
25
Sidewall
patent
glazing
Extruded
aluminium
glazing bar
-6 mm glass
Aluminiumcapping
600
C/S of bars
Neoprene
sealerstrip
6 mm glassExtruded
aluminium bar
Aluminium capping
Stainless
steel screws600
Cs of bars
DETAIL B
Concreteslab
o
2 371
w
Aluminiumclosure
Overall length of glazing bar
Compo
bedding
6 mm
glass
Draughtfillet
Concreteslab
Figure 4.29 Aluminium window glazing
Fixing plugs
at head
and sill
Aluminium
muntin used
where two
types of glass
are required
in one fler
2 400
Aluminiumsil
SECTION C-C
.
4.8 PAINTING AND DECORATING
The guidelines in this section (4.8) have been adapted from the Council for
Scientific and Industrial Research's "A Technical Guide to Good House
Construction" (1978:173-177) and are hereby acknowledged.
Paints are composed of two general ingreciients, the pigments and a liquid, which
changes to a solid film when painted and dried. Dryers may be added to increase
the rate of crying, and solvents or thinners to adjust viscosity or to assist application.
The liquid used in the paint is referred to as the "basis” of the paint. All paints are
thus “based" on a specific liquid.
It should always be borne in mind that the durability of any paint coating depends
very much on the thickness of the paint. Thai, however, does not mean thaí each
coat of paint should be applied as thickly as possible.
A coat that is applied too thick will cause the paint to sag and run, and will give
rise to other problems such as slow drying, wrinkling, poor gloss of the final coat,
etc. A thick coating is achieved by applying several coats of the same type of
paint. When painting a new surface, always start off with the right primer.
Different primers are available for galvanised iron, steel, wood and even concrete
and plastered surfaces, and in each case the primer serves a special function.
Primers in general are paints specially formulated to give good adhesion to the
surface for which they are intended. So for wood, concrete and plastered
surfaces, the binder of the primer is such that it penetrates the surface in order
to give good adhesion and at the same time to bind the pigment into a proper
film. Primers for asbestos cement, concrete and plastered surfaces are
normally also resistant to the alkaline surface to which they are applied, whereas
primers intended for metal surfaces contain corrosion-inhibitive pigments
protecting the surface from any spreading of corrosion if the paint surface should
be damaged.
After the primer has cried, an undercoat should be applied. The undercoat serves
a fourfold purpose. Firstly, it provides a good bond between the primer and the
finishing coat. Secondly, it is a relatively cheap paint which helps to add to the
thickness of the final paint film thereby giving the required thickness for a durable
paint coating system as pointed out above. Thirdly, when cry, it can be sanded
lightly should there be any roughness in the surface; this will ensure a smooth
finish when the finishing coat is applied. A very fine grade of sandpaper should
be used as heavy sanding will take off all the paint in patches, leaving weak spots
in the film where early paint iailure may occur. In the fourth place, it has the
purpose of maintaining the appearance of the finishing coat. This imeans that
although the undercoat has a somewhat absorbent suriace, it is so formulaied
that it allows the finishing coai to maintain its ability to dry to its normal finish. undercoat has dried
properly, dust it off before applying ihe final coai.
The finishing coat's function is to provide a durable water and weather resistant
finisi, providing the necessary protection to the underlying primer and undercoat.
It adheres well to the undercoat, provides the desired colour and finish, and
normally has good flow and application properties so as to achieve a smooti
professional finish. Each coat of paint therefore plays its part in forming the
complete paint system.
The above types of paint apply only to solvent-based paints. Water-borne
(emulsion) paints are self-priming and need no undercoat.
All paints must be properly stirred to ensure that they are well mixed. Always
read and follow the manufacturer's instructions – these are usually printed on
the label of the tin.
Some paints dry faster than others and can be ready for the next coat within a
few hours but, unless otherwise indicated in the manufacturer's instructions, it is
best to leave a coat of paint to cry overnight before applying the next coat.
4.8.1 Types of paint
Different paints are required to perform varied functions. The qualities to be
expected from a paint system include some or all of the following: adhesion to the surface being painted
impermeability to water (liquid)
permeability to water vapour
protection, including shielding the material being painted from the effects of
the weather, steam (e. g. in a kitchen) and wear and tear
obliteration oi any unsightly marks and stains
decorativeness, including imparting the desired colour or texture
elasticity, i. e. an ability to accommodate thermal movements of the painteci
material
durability
A paint system usually has the following components:
Knotting for wood)
Shellac is the basis of "knotting solution", which, although noi really a paini,
is applied to knots in new timber to prevent the natural resins in the timber
from damaging the succeeding. coats. PVA (polyvinyl acetate) paints are also
frequently used for this purpose.
The primer
The function of the primer is to proteci the maierial being painted and to
provide a surface io which subsequent coats will adhere. There are various
types inade either to seal porous surfaces such as softwoods, plaster or
brickwork, or to protect metallic surfaces from rust or corrosion, or even to
bind smooth surfaces.
The undercoat
This layer must completely blot out any unsightly rarks on the surface being
painted and adds to the total thickness that contributes to the life of the paint
system. The undercoai also dries to a matt surface to provide a good grip
for the topcoat.
The topcoat (final or finishing coat)
This is the layer that must provide the desired finish, colour and texture, and
the resilience that protects the paint sysiem from damage. The topcoat is
the only one of the three that dries with a surface that is not always suitable
for painting on - a fact which is often a cause of failure in repainting jobs.
Each of these paint types generally contains some or all of the following
basic ingredients:
a binder
a drier
a solveri (the basis)
a pigment
Nowadays there are literally thousands of chemicals that could be used in
paints with the result that it is important when specifying a paint system thai
the various coats are all compatible. The simple solution is to ensure that
the complete paint system - the primer, undercoat and topcoat - are as
recommended for ihe purpose by the same manufacturer.
Principle kinds of topcoats available
Limewash
The main constituents of limewash are lime, sodium chloride and iallow
or oil. Although once used extensively for outside plasierwork, limewash
has now largely given way to emulsion paint for new work.
Distemper
The pigment is often bound with ordinary water-soluble glue or size,
although oil-bound distempers are also made. Although cheap, distemper
is not used much today and cannot be used externally. As with limewash,
its big disadvantage is that recoating with any other type of paint at a
later stage usually involves complete stripping of ihe initial coating.
Oll paint
This is the traditional "enamel" paint in which a long-lasting pigmeni
such as titanium dioxide is bound with a drying oil such as linseed,
soya or sunflower seed oil. Although oil paints of this type have been
largely superseded, they are still successfully used on some surfaces,
particularly external woodwork.
Alkyd resin paint
When normal drying oils are chemically treated they can produce a family
of synthetic compounds known as alkyds. They have more flexibility than
the traditional oil paints and at present form the bulk of "gloss enamel"
paints sold.
PVA (polyvinyl acetate) and similar emulsion paints
This group sometimes referred to as “plastic paints", includes PVA,
PVA-acrylics, acrylics, PVA-maleates, and various other polymers and
co-polymers. In America, these are usually referred to as latex paints.
Water is the basis of all paints of this type.
Among the reasons for the popularity of these paints are that they are
water-dispersable prior to setting, enabling them to be easily thinned,
and ihat brushes and rollers can be cleaned using water. Another
advantage is their rapid recoatability.
They are also alkali resistant, which makes them very useful for applying
io fresh cement work. These paints are relatively porous when drying
which makes them able to "breathe" and therefore less likely to be forced
off the wall by water vapour from within.
PU (polyurethane paint)
This is a syniheiic resin paint that is extremely durable and can be used
on most surfaces. It is available as a one or two-pack system. However,
ihere can be problems due to loss of adhesion on some surfaces. Special
solvents must be used for thinning and brush-cleaning.
Epoxy paints and coatings
Epoxies are amongsi the hardesi resins known and, wien correcily
appliec to a sciupulously clean surface, have exceptionally good adhesion
characteristics. They can be loaded with pigment and fibre and are the
basis of the more successful one-coat painting systems. They are not
cominonly used in conveniional construction but are useful in specific
situations for the protection of metal surfaces against corrosion and for
camp-proofing the surfaces of concrete surface beds and mortar
screeds.
Epoxies can, however, present serious problems where a second coat
is needed after a time, or where a surface has to be repainted, as it
does not receive further coats successfully due to a lack of adhesion.
Special solvents are norinally required for thinning and cleaning of
equipment.
Chlorinated rubber paint
Chlorinated paints are extremely resistant to water penetration and
chemical attack and are used io good effect on metals in marine
environments. However, some formulations have poor flexibility and low
resistance to heat. They are also used on cement-based surfaces for
certain applications, e. g. swimming pools. Chlorinated rubber thinners
should be used as a solvent.
Clear finishes and stains
Clear finishes include the shellacs, lacquers, polyesters, polyurethane
varnishes and phenol-formaldehyde resin varnishes, and are mainly used
on wood surfaces.
The protection offered by clear finishes is generally inferior to that offered
by opaque coatings, i. e. paints. Although many of these products may
be used successfully internally, few are suitable for use externally.
For internal woodwork, short-oil varnishes or spirit varnishes containing
shellac have tracitionally been used. Short-oil varnishes have a higher
proportion of resin than long-oil varnishes and they generally dry more
quickly, are harder anci exhibit a higher gloss. The polyester varnishes
commonly used nowadays are more impact, abrasion and stain resistant
and also far less brittle.
For external woodwork, long-oil varnishes and other products inay be
used, but their life is generally short. The polyurethane varnishes
currently available are not suitable for use outdoors. A water-repellent
stain will give far better results where a natural finish is required for
timber exposed to the weaiher.
Preparation of the surface
Preparing the surface correctly is an essential step to achieving good
adhesion and a satisfactory texture.
Wood
For best results timber should be ai "equilibrium moisture content" wihen
it is painted. It should, as far as possible, be protected from the weather
before being painted. The wood must be sanded smooth, all dust
removed and all cracks, splits and nail-holes stopped with a suitable
iller. A suitable knotting solution should be applied to all knots and
then be sanded smooth.
Timber musi noi be painted when it is wet or even damp.
Meta!
Grit blasting is the best method of preparing steel for painting..
Unfortunately this is not always possible on a building site. ivietal musi
be completely free from all dust, grease and rust. A technique for
galvanised steel is to brush it down hard with a stiff wire brush and then
to rub the surface with a steel pot scourer or sandpaper. A rust remover
should then be applied to the surface, which should be thoroughly
washed off on completior.. The surface must be thoroughly dry before
the primer is applied. Priming must always be undertaken immediately
after cleaning, otherwise rusting of the metal will again take place.
For galvanised and ungalvanised steel, special cleaning pastes or
detergents are available to remove the protective oil coat or wax
applied at the factory. The cleaner must be washed off thoroughly and
the steel allowed to dry before paint is applied. Using the above
cleaning agents and the right paint, correctly applied, it is no longer
considered necessary to allow galvanised surfaces to weather before
painting.
Gament-work
A concrete or plastered wall should be washed down thoroughly with
water and detergent, and then well rinsed and allowed to dry before
being painted. All surface irregularities, cracks and inoles should also
be filled and sandpapered smooth before painting.
Particular attention should be given to the removal of any mouldi (shutter)
oil on concrete. "Glazed areas" on concrete shoulci also be roughened
before painting. This is liable to occur where plastic inoulds have been
used.
Some suggestions for painting various surfaces
Paints for ungalvanised steal
All surfaces of steel components should be given a coat of the appropriate
primer, after having cleaned ihe surface with a solvent in the factory
before delivery to site. For exposed steel which will not be subjected to
the climatic conditions of the coastal areas and the Cape Peninsula, a
system of preparation, priming paints, and appropriate overlayers
conforming to ihe relevant SABS codes of practice and standard
specifications should be used. The total dry-film thickness of the paint
film should not be less than 100 micrometres. Methods of preparing the
steel for painting and the types of coating to be used should be selected
from the SABS schedules appropriate to the building method used, e. g.
SABS 064, 312, 630, 631, 681, 684, 801 and 912.
For exposed steel subjected to the climatic conditions of the coastal
areas, the steel should be blast-cleaned, or pickled in an acid bath and
coated with two layers of red-lead priming paint to SABS 312, Type 2
Grade 1, followed by two layers of micaceous iron-oxide oil or oleoresinous paint, and over-coated with
a finishing paint to SABS 684,
Type A or B.
Red-lead type priming paints do not generally lend themselves to
prefabricated building methods, owing to their rather long drying tiine.
Another imethod of painting steel for protection under the climatic
conditions in the coastal areas may therefore have to be used. Other
choices include a high-build chiorinated rubber paint system or a system
incorporating phenolic-based pigmented etch primer and micaceous
iron-oxide paini.
Paints for galvanised steel
Any areas of steel components where the galvanised coating becomes
damaged should immecliately be touched up with the appropriate primer
prior to building in or fixing. Exposed galvanised steel which will not be
subjected to the conditions of the coastal areas should be coated with
calcium-plumbate priming paint to SABS 912 after the surface has been
properly cleaned, followed by emulsion paint to SABS 940, or roof paint
to SABS 583, Type A or B. iiicaceous iron oxide paint is also
successful. The manufacturer of steel roofing sheets, for example,
ofien applies temporary protective coatings (such as wax) at the ſactory
to enable the product to be transported and stored with a minimum of
corrosion problems.
All traces of such storage oil, wax or resin on galvanised steel musi
therefore be properly cleaned off with a special abrasive cleaner or
cietergeni before painting.
For corrugated steel roofs, a single-layer coating which provides longlasting protection iſ applied over
scrupulously cleaned, new galvanised
steel sheeting, is emulsion-type roof paint to SABS 940. Galvanised
units destined for use in the coastal areas will require different paint
systems, such as one of the following: one coai of calcium-plumbate priming paint to SABS 912 followed
by two coats of roof paint to SABS 683, Type A or B, or two coats
of micaceous iron-oxide alkyd paint;
one coat of etch primer, followed by one coat of zinc-chromate primer,
one coat of micaceous iron-oxide alkyd paint, and a finishing coaiof paint to SABS 684, Type B, or SABS
683, Type B.
In coastal areas, corrosion is extremely likely to occur at laps in the
roof where moisture can collect. It is therefore essential that these
areas are adequately protected by one of the above paint systems
before erection. Factory precoated galvanised steel roofing sheets,
which can be used in coastal areas, are also available.
Paints for aluminium
Before aluminium is painted any oxices that may have formed on the
surface should be removed. Cleaning should be followed by the
application of a wash-primer conforming to SABS 723, and thereafter, a
zinc-chromatic primer to SABS 679, Type 1. An undercoat and a topcoat
should then be applied.
Paints for wood
After cleaning the surface of the wood, which should be at the equilibrium
moisture content, the knots and resin pockets should be coated with
one layer of knotting varnish. Thereafter, one coat of primring paint to
SABS 678, Type II, should be applied, followed by one layer of undercoat
paint to SABS 681, and one or iwo finishing coats of paint to SABS 530.
In the case of timber exposed to the weather, pre-oiling generally extends
the lifespan of the paini system. This can be accomplished by brushing
a 50:50 solution of linseed oil and mineral turpentine over the cleaneddow'n surfaces. Afier about an
hour the surface should be wiped with a
cloth to remove excess solution not absorbed by the timber. Painting
should begin the following day.
The main function of a paini on exposed timber is to protect it against
the weather and, in particular, water entry. However, regardless of the
effectiveness of a finish as a water barrier, entry can occur at butt ends,
joints and small cracks that may develop after a period. If, as a result of
this, the wood becomes wet for prolonged periods, it is subject to decay
unless it has been pre-treated with a suitable preservative. Softwoodis
are particularly prone to decay under these circumstances unless
protected. It is therefore recommended that all softwoods (coniferous)
exposed to the weather and which are to be painted should, prior to
installation, be ireated with preservative in accordance with SABS 05.
Where timber exposed to the weather has not been treated in this way,
it is preferable to apply a water-repellent stain instead of a paint. At
least iwo layers of water-repellent stain should be applied. li is usually
available in "natural" forin and in various "wood tints",
Paints for plastered walls
Two coats of emulsion paint conforming to SABS 633 or 634, as
appropriate, should be used. For bathrooms and kitchens it is
suggested that SABS 634, poly-acrylic type, be used. Filler coats are
not recommended for use on exterior walls.
Oil-bound and alkyd resin paints may also be used for plastered walls,
but because new cement always contains an excess of alkali in the form
of lime, these paints can deteriorate under moist conditions if applied to
such surfaces. The oils in some paints saponify (form soap) when they
come into contact with alkalis. With an oil-based paint system, a
proprietary sealer should first be applied to the wall, but the danger oí
trapping damp behind the layer of paini still exists with this system.
Paints for asbestos-cement boarding, shesting and panels
Two coais of polyurethane paint (two-pack type) should be applied, or one
coat of resinous wall sealer, followed by two coats of acrylic emulsion
paint to SABS 634. A single layer only of the sealer should be applied.
The build-up of a continuous glossy layer should, however, be avoided.
Particularly where the latter paint system is to be used, it is importani
inat ali nail and screw-heads are touched-up with calcium plumbate or
oiher suitable primer before painting.
Paints for concreta
Two coais oſ acrylic emulsion paini to SABS 634 should be applied on
external concrete surfaces, or, one coat of oleo-resinous bonding liquid
followed by two coats of PVA CO-polymer emulsion paint to SABS 634.
Internal concrete surfaces should have one coat of oleo-resinous bonding
liquid followed by two coats of PVA co-polymer emulsion paint to SABS
633.
The use of gypsum plaster or gypsum containing fillers for levelling should
be avoided externally and in any areas where damp conditions are likely
to prevail.
A cement paint may also be used, but its application requires considerable
care and the manufacturer's instructions should be strictly followed.
Common paint fallures
The following are some of the mosi common paint failures and the reasons
for them.
Blistering
This is often caused by moisture or grease trapped below the paint surface,
which, when the surface is later subjected to heat, as from the sun, vaporise
and fom blisters in the paint film. Problems of this kind can be obviated if
the surface to be painted is properly prepared and cleaned.
Alligatoring
This disfiguring break-up of the surface texture of a paint system is usually
caused by incompatibility between the various coats of the paint system,
too rapid surface drying, or even too ihick a coating.
Cracking
This may occur with paint on woodwork where the wood was not properly
diy prior to painting or where a hard-drying paint or varnish is used which
cannot accommodate movements caused by temperature, moisture and
impact.
Flaking
This is usually caused by inacequate preparation of ihe surface to be
painted. Flaking following loss of adhesion occurs because the surface
was ioo smooth or was not properly cleaned, as with the protective oils
on new galvanisec steel. It may also be caused by the use of an unsuitable
primer.
Failure to dry properly
If non-drying oil, wax or grease are allowed to become inixed with the
paint, it may remain tacky almost indefinitely.
Chalking
This is the result of natural elements such as ultra-violet light destroying
the binder so that the pigment comes off as a powder. All paints are
eventually degraded in this way and it is generally regarded as a fault
only when it takes place too soon afier application.
Fading
Where this occurs prematurely, it may be because paint meani for
internal use has been used externally.
4.8.2 Paperhanging
Wallpapering is a decorative finish which can easily be renewed. Wallpapers are
made to standard widths in rolls, and used primarily as a high class wall finish. A
wide variety is available for use as part of the interior decorating process, including
the following: Plain or pulp papers: the primary material is paper with patterns or pictures
printed on it.
Flock papers: the pattern is printed on a tinted paper in a sticky colourless
composition. Flock is then dusted over the paper, and by adhering only to
the sticky parts, forms the pattern.
Ingrain papers: ordinary or pulp papers into which a specially prepared
fibre is incorporated. These papers are made both plain and ornamenta!.
Embossed papers: made principally form pulp, the pattern being ſormed by
raising or embossing the surface.
Plastic-coated papers: with a thin plastic surface boncied to a paper base,
which can be coloured and patterned in endless varieties. This is ihe mosi
commonly used wallpaper.
The "hanging" of wallpaper
The correct choice of pasie is essential because different papers require
different types of pasie. There are three basic classes of pasie: those baseci on starch and flour, of which
there are three iypes, namely
hoi water, cold water and tub paste;
D
those coniaining water (soluble cellulose ethers) which require care in
their use because they give excessive penetration of water on some
papers;
pre-glued wall papers.
Plastic-coated papers require a paste that contains fungicide, in order to
prevent the development of moulds beneath their impervious surface.
However, most wallpapers nowadays are pre-glued. All that is necessary is
to wet the paper with water and it is ready to hang.
The old method of using glue has been mentioned because care must be
taken when repapering to ensure that the glues are compatible. In the cost
calculation it will make quite a difference if the old wall paper has to be strippeci
down to the plaster or if the new wall paper can be hung directly over the old
paper.
Wallpaper is now always sold ready trimmed and is hung with its edges
butting against one anoiher (without overlap), the first length being hung to a
plumbline. The work is started at the lighter end of a room, working away
from the light so that any inadvertent overlap casts the minimum of shadow.
Ceiling paper is hung similarly, but instead of using a plumbline to set the first
length, this is done by measuring and striking a guide line on the ceiling.
4.9 MEMBRANE WATERPROOFING
The main aspect which will be dealt with here is waterproofing of flat concrete
rooís. Whatever waterproofing system for flat roofs is used, the work should be
entrusted to a contractor specialising in the particular system.
The iníormation in this section (4.9) has been adapted from the Council for Scientific
and Industrial Research's "A Technical Guide to Good House Construction."
(1978:130-136) and is hereby acknowledged.
4.9,1 Definitions
The following definitions are applicable in this chapter: Adhesive (cold): The material used to bond
waterproofing membranes,
applied withoui heating.
Adhesive (hot): The bitumen-based material wirich is applied hot to stick
membranes to underlying surfaces.
Asphaltic compound: A compound based on bitumen and an inert filler.
Bituminous compound: A suitable mixture of bituminous binder and filling
maierial.
Black sheathing felt: A coarse impregnaied felt not coated with tar or bitumen.
Dry: Refers to dry surface conditions.
Felt: A material that is "felted” by interlocking the fibres and is then pressed
and cut into sheets.
Foot traffic: Traffic on the roof or similar outdoor recreation area where potplanis, garden chairs and
other heavy objects may be placed.
Impregnated felt: A felt saturated with bitumen.
Joint sealing compound: A material used for making joints watertight.
iviastic asphalt: Asphali containing suitably graded mineral matter to form
an impermeabie mass, iluid enough to be spread by means of a hand floai
when heated.
Primer: A bitumen io which a suitable volatile solvent has been added and
which is used to prepare a surface for the operation that is to follow.
Roofing felt (coated felt): A felt saturated and coated with bitumen-based
compound on both sides.
Acrylic waterproofing system: Consists of a primer, saturator, fibre glass felt
and a top coat available in a variety of attractive colours.
4.9.2 General comments
Goverings
Preference should be given to inaterials obtainable in accordance with SABS
standard specifications. Roof coverings may consist of mastic asphalt,
biiuminous felt, synthetic rubber, polymers or a proprietary material. All these
roof coverings should be protected from the elements by one of the following:
bituminous aluminium paint
tiles (of clay, concrete, asbestos-cemeni or naiural stone)
slate
stone chippings or pebbles
emulsion on bicicun.
If bituininous aluminium paint is used as a proiective coating, the covering
should be inspected at 12-monthly intervals and, if necessary, repainted.
Covering the top surface with tiles or paving slabs will have the additional
advantages that both solar heat gains and thermal movement of the roof
itself will be considerably reduced. Hollow clay tiles are particularly effective
for this purpose.
Application of coverings
Normally app! ied to flat or low-slope roofs of less than 10 degrees.
Surface to be covered
This should be firm, smooih, dry and continuous, without ridges and with
adequate provision for expansion and contraction, which should not exceed
the ability of the covering used.
The surface on which the covering is laid musi have a minimum fall of 1 in 50
(approximately 1 1/2 degrees).
A suitable mix for a screed to receive waterproofing is 1 part of cement to 5
parts of clean aggregate, by volume. Lightweight aggregates are sometimes
used for screeds, which also provide thermal insulation.
Fiashings
Flashings are a very important element of membrane waterproofing as
Gefective flashings are one of the main causes of leaks. Details recommended
by manufacturers should be strictly adhered to. Some detailing will be
discussed in ihe following text.
4.9.3 Mastic asphalt roof coverings
Materials
iviastic asphalt should comply with the requiremenis of SABS 297. li is
delivered to site in a solid state, usually in blocks and chunks up to 300 mm
square or diameter, which is then imelted in a heated pot and applied by trowel.
Details of applicationIt is essential thai an underlay is used over all surfaces that are to receive
mastic asphali as it allows relative movement between the asphalt and
the deck, and prevenis rapid cooling and blowing due to vapours on
camp concrete surfaces. The underlay may be a black sheathing feli,
thick building paper or lighiweight rooſing felt.
Each coat of mastic asphalt should be applied in bays whose eciges do
not coincide with the edges of other coais or with the joinis of any
underlay Lised. No bay may include a change of slope, and may therefore
not traverse either a run-off or a ridge line. Any mastic asphalt work left
uniinished should be warmed up and cleaned at the edges before fresh
material is laid next to it.
The mastic asphalt should preferably be applied in two layers with a
resulting total thickness of not less than 20 mm, but may be applied in
one single layer of at least 15 mm thick. With one-layer applications the
joints need particularly careful treatment.
For each coat of mastic asphalt, thickness gauges should be used. On
no accouni should nails or the like be driven into previous work to set
levels for the following application.
In all cases where the mastic asphalt abuts against parapet walls,
chimney stacks or oiher upstands, a fillei should be constructed with
mastic asphalt anci a skirting, formed in the manner shown in figure 4.30
and a metal cover flashing should also be used.
Where mastic asphalt is taken over an external angle, care should be
taken io maintain the fuld thickness of the coat.
The finished mastic asphalt should be adequately protected from the
weather. This may be achieved by coating the surface with a bitumenbased paint, preferably aluminium,
or a paint or similar reflective properties,
or by applying a layer of stone chippings.
Brickwork in stretcher
bond with wire tiles
Bituminous compound
Precast coping
bedded in mortar
DPC
110 mm wide over
wall joint
Metal cover flashing
Mastic asphalt skirtingMastic asphalt
-Underlay
Screed to falls
Figure 4.30 Typical mastic asphalt waterproofing
Mastic asphalt with a tiled covering
Materiais
The mastic asphalt used as the waterproofing should consist of a mixture
oſ soluble bitumen complying with SABS 297 and suitably graded mineral
aggregate. Asbestos-cement, burnt clay, cast stone, concrete, terrazzo
and slate have been used successfully as a tiled weather-resistant
aggregate in this iype of construction.
Deialis of application
At leasi iwo coats of mastic asphalt with a total thickness of not less than
20 mm should be laid. Tiles, slates or paving slabs are then bedded in
cement mortar on a slip-layer of polyethylene sheeting on the mastic
asphalt. The joints between tiles or slates should be solidly filled with
mortar with expansion joints provided at not more than 3 m centres both
ways. For lighter types of tile covering, bituminous adhesive may be used
in lieu of cement mortar, in which case the tiles could be butt-jointed.
4.9.4 Bituminous felt roof coverings
Materials
Coated felts (mineral-stabilised bitumen roofing felts surfaced with finely
powdered mineral matter) should comply with SABS 92.
The jointing compound should be:
a hot jointing compound complying with SABS 317; or
a cold adhesive in the form of a bitumen emulsion; or
a rubberised bitumen cement containing a solvent.
Details of applicationThe felt is laid in strips, at least iwo layers thick with hot-sealed overlaps
as shown in figure 4.31.
Before laying, the felt inembrane is first prepared by cutiing it into lengths
which should not exceed 7 m and which are left exposed for as long as
possible, to allow them to expand before laying. Where end joints occur,
an overlap of at least 150 mm should be made and sealed. Whenever
practicable, the felt should be laid across the fall of the rooi.
At leasi two layers of coated feli should be used. The layers of felt are
siuck continuously to each other with hot or cold bituminous compound,
but the suriace in contact with the deck should not be stuck down
continuously. It should be left unbonded or partially bonded sufficiently
to prevent wind “uplift". However, where the deck is of concrete and the
slope exceeds 7 degrees the felt should be fully sealed to the deck.
Sheeing around pipes and outlets should only be sealed to a previously
primed surface for a width of 150 to 200 mm.
If cold adhesive is used, the sheets should be rolled immediately with a
roller weighing about 50 kg to expel any air trapped between sheets and
to ensure good overall adhesion.
In all cases where the bituminous felt covering abuts against parapet
walls or other upstands, a fillet should be constructed and a skirting
for. med. A metal cover flashing should also be used.
For durability, a blinding of fine aggregate, or a coat of bitumen-based
aluminium paint may be applied.
Galvanised metal or bituminous feltCover flashing
75 x 75 mm corner
Concrete roof slab
Screed to falls
Bituminous felt
waterproofing
Cover flashing
Commence first layer with 500 mm width,
thereafter use 1 m widths with 50 mm laps
Figure 4.31 Two layer bituminous felt waterproofing
Bituminous fait with a tile covering
Rainwater
outlet
Materials
The felts and jointing compounds should conform io those described
above and the üle to be used for the covering may be chosen from the
following: asbestos-cement, burnt clay, concreie, terrazzo or casi
sione.
Details of appilcation
Tiles inay either be laid in a flood coating of hoi bitumen or a cold applied
asbestos-filled bitumen compound may be applied, but this should be
allowed to cure thoroughly before tiles are laid.
When tiles are to be bedded in cement mortar, a flood coat of hot
bitumen should first be applied to the membrane to protect it. Loose
laid tiles are not recommended where regular foot traffic exists as
movement of the tiles can damage the membrane.
For occasional foot traffic, paving slabs with raised studs on the undersurface may be used, with noi less
than 25 mm clearance. The studding
will reduce the movement and will also prevent moisture from accumulating
between the üle and the felt.
4.9.5 Elastomeric roof coverings
Materiais
Elastomeric materials such as chloroprene rubber should comply with SABS
580 and should not be less than 1,6 mm in thickness. The jointing
compound used for sealing the sheeting should be approved by the
manufacturer of the sheeting.
Details of applicationSheets are laid with side and end laps not less than 100 mm.
Before any adhesive is appliec, the sections of the sireet should be
thoroughly prepared by sanding or solvent cleaning. Depending on the
structure and iocal requirements, a glue line of not less than 100 mm at
intervals of 1,5 m should be applied.
Sheeting around pipes and outlets should be sealed io a previously
priined surface for a width of 150-200 mm anci ſlashed.
Whenever practical, each sheet should be laid across the fall of the rooí.
The joints should be rolled immediately with a small hand roller to expel
any air trapped in the joints and to ensure good overall adhesion.
In all cases where the elastomeric waterproofing covering abuts against
parapei walls or other upstancis, a fillet skirting is formed. A metal cover
ilashing should be used.
For durability, the application should be finished off with two coais of
approved paint.
in areas which will be trafficable, a protective underlay of bituininous
sheeting, butt-jointed with ihe joints sealed to the screed, should be used
before the elastomeric sheeting has been laid, with a further protective
layer of bituminous sheeting lapped for a minimum of 100 mm laid over
the elastomeric sheeting where traffic occurs.
4.9.5 Expansion joints
Where expansion joints are necessary in the roof, care should be taken to inake
a weather-tight joint.
The raised-icerb type of joint is preferred, as in the example shown in figure 4.32.
Metal flashing
Metal clips at 1000 mm intervalsFlashing notched
and bent under clips
Layers of bituminous
felt covering
Screed
Cover strip fixed one side only
Figure 4.32 Raised-kerb expansion joint
4.9.7 Condensation and thermal insulation of concrete roofs
Genera!
The purpose of insulating concrete roofs is twofold. It is firstly to prevent
solar heat gains or loss through the roof, thus ensuring better indoor thermal
conditions, and secondly to reduce thermal movement of the roof itself. In
order io achieve this, the insulation should be applied on top of the roof slab,
below the screed. It should, however, be realised that the use of themal
insulation can increase the possibilities of condensation because of the
inevitable reduction in surface temperatures on the inside of the building.
vioisture condensed beneath the waterproofing in this imanner may evaporate
in subsequent hot weather. Pressure build-up may be sufficient to damage
the membrane or tear ii loose from the slab, forming bubbles. The problem
is particularly severe where it is not possible to allow the slab to dry out
sufficiently before being waterproofed.
There are several ways of reducing rooi temperatures or heat gains and
losses through concrete roofs, such as:
Non-trafficable surfaces
Insulation of concrete roofs is the most satisfactory method for improved
thermal conditions in buildings. The best insulation materials are those
with a low affinity for moisture. A layer of 20 mm thick foamed
polyurethane or 25 mm thick polystyrene or high-density mineral wool
will normally be suitable for the purpose. It is important to ensure that a
dimensionally stable type of insulation that is able to support the load, is
used. Ventilation can be achieved by cross-wise channels approximately
20 mm wide in the insulation itself. The ventilation channels in the
insulation should be located as close as possible to the waterproofing,
where condensation is most likely to occur. The moisture should be
disposed of directly to the outside air by means of openings or pipes in
parapets. These openings at roof edges should be protected against
rain penetration.
A layer of non-bituminous building paper should be laid over the insulation
before pouring the screed. The screed should be at least 60 mm thick
and reinforced with mesh reinforcement. The waterproofing membrane
is then laid on top of the screed as usual. There are other methods of
construction, which include putting the insulation on top of the graded
slab or screed, and laying the waterproofing membrane directly over this.
This however is not recommended.
Painting with an aluminium bitumen-based paini, or light coloured paints,
are fairly effective in reducing solar heat gains due to reflection, but it has
practical limitations. Accumulation of dirt soon renders it ineffective, and
this necessitates repainting at regular intervals. Light-coloureci marble or
stone chips may also be used.
The use of paving üles, as describeci previously, is also effective in limiting
solar heat gains and should be considered even where a trafficable
surface is not essential.
Construction to suit foot traffic
Another method of reducing adverse climatic efíects to ensure better
incioor thermal conditions, is the use of tiles above the waterproofing.
These may be used insiead of or in addition to the roof insulation
discussed earlier in this section. Hollow clay tiles cut in half and laid
with the cut side downwards are known to give good results because of
the additional resistance to heat flow afforded by the air spaces. Solid
paving tiles 25 to 40 mm thick of precast concreie, asbestos-cement or
burnt clay also give satisfactory results.
However, care should be exercised in the use of loose üles for flai roofs
that have no parapets or only very low ones. The tiles should be attached
io each other properly, or secured by some other means so that they are
noi lifted by high winds. This applies in particular to the areas near the
corners of buildings where local suctions or depressions in air pressure
created by winds can be sufficient to lift even relatively heavy tiles.
Comment
Insulation of all roofs, whether light-weight or heavy-weight, is desirable
under South African climatic conditions. Correct application of insulation
is, however, of the utmost importance, otherwise it can increase the
possibilities of condensation problem. s.
4.10 PAVING AND ROADS
Paving blocks date back to Greek and Roman times. For modern vehicular and
pedestrian use a wide range of block designs are available. Interlocking paving
blocks are functional and decorative. The modern demand is for hand-sized,
easy-to-lay, self-locating, top-chamfered, interlocking concrete paving blocks, of
consistently high quality wearing surface which provide a fully bonded surface ai
a reasonable cost. iviinimal expertise and mechanical plant is required for laying
on a suitably prepared sub-base without mortar.
Burnt clay bricks can also be used for paving. High quality clay bricks are used
for long wearing and aesthetical reasons. Beautiful colours are available in natural
clay products. The clay bricks can be laid loose or in mortar with the joints neatly
pointed. Cobble stone paving (broken bricks, normally stock bricks) are laid in
patterns with the joints filled with a 1:3 cement and river sand mixture.
Concrete paving may be laid in panels and should be at least 75 mm thick, or
90 mm thick iſ cast in strips. In order to prevent cracking, panel dimensions
should not exceed 2,5 m in length or width. The concrete can be coloured by
adding a colouring ageni. Various patterns can be pressed in the wet concrete
to obtain the desired finish, also forming expansion joints in the same operation.
Tarred suriaces are often cheaper than paved suifaces. The most importani
aspect which determines both the life and the aesthetic appeal of paved and
tarred surfaces is the preparation of the earth (soil) underneath the suríace area,
called the base.
4.10.1 Preparing the base
To prepare the base to receive a surface ireatment, siart by evaluating the quality
of the soil. The same principles ihat apply to the soil under building foundations,
apply to surface area base material. Cracking in the surface areas are however
of less importance when brick or block paving is used (as the joints permit
movement) ihan in tarred surfaces.
The general principle however, is that clay is unacceptable as is sand in thick,
uncontained siiuations. Generally the base preparation will require the following: Clay or sand are io be
removed and replaced with a stable inaterial which
can be compacted to a high density.
Good quality stable soils can be levelled and compacted to the required
density. In instances where the soil is loose or disturbed by building activity,
it is advisable to scarify the entire area to a depth of at least 150 mm ard
ihen to recompact to the same density over the entire area.
The preparation of the base to receive iar is very critical. Tar flexibility is
limited and cracking occurs if the base is not very stable and dense. The
final base layer is usually of crushed stone (crusher run) which can be
compacted to a high density.
4.10.2 Tarred surfaces
Tarred surfaces are available in three main categories: Spray and chip is the common name for cold or
hot tar being sprayed onto
the base (preceded by a primer) and then covered with a layer of small
stone (chip). The quality is determined by the number of layers and thus the
eventual thickness, which could be between 6 mm and 50 mm in standard
applications.
Mastic asphalt is a bituminous mix (sand, stone and bitumen) placed in hot or
cold layers by machine, either on a spray and chip surface, or on a priined
surface.
A premixed cold tar is also available with a water base. It is mixed like moriar
with water and generally applied in mainienance work.
li is common practice to engage a consulting engineer to design tarred or paved
surfaces io ensure proper functioning in heavy traffic situations.
4.10.3 Concrete paving blocks
These blocks are available in mainly two thicknesses, namely 60 mm and 80 mm.
The ihinner concrete blocks are used for gardien paving, pedestrian and lighttraffic areas. Industrial
areas, access roads and parking areas should be paved
with 80 mm thick blocks.
Ordinary bevelled edge concrete blocks are rectangular in shape with the top
sicie edges slightly bevelled. Colouring, if required, is done in the top 10 mm
of the block. These blocks are normally used for garden paving. See figure
4.33.
Interlocking blocks interlock on 4 sides with 6 surrounding blocks. The
vertical load on one block is supported by its neighbour, spreading the load
stresses to adjacent blocks. This interlocking action prevents horizontal
"creep" due to vehicular movement. See figure 4.33.
INTERLOCKING PAVING BLOCKS WITH
BEVELLED EDGE
RECTANGULAR BEVELLED EDGE PAVING BLOCKS
Figure 4.33 Interlocking and rectangular bevelled edgepaving
4.10.4 Bonding
Rectangular and other non-standard inierlocking paving blocks can be laid in a
variety of pleasing patterns. The most commonly used bonding is herringbone
bond, streicher bond, baskei weave bond, and parquet bond.
4.10.5 Prevention of puddle formation
To prevent ihe formation of puddles from rain water and the possible resultant
softening of the underlying ground, paving should not be absolutely horizontal.
A slope of at least i in 50 (20 mm in 1 m) should be provided to divert water to
stormwater drains. Sudden changes of slope or too steep falls (more than 1:30)
should be avoided, particularly if the paving is to be used by vehicles.
4.10.6 Treatment of the ground
The area to be pavedi should be excavated or filled as necessary to the correct
level to accomplish a sound base. Before placing the sand bed, the ground may
be treated if so required, with suitable soil insecticide to discourage ants or termites
from undermining the paving. Aldrin or chlordane types of insecticides will be
suitable and should be applied according to the manufacturer's instructions.
Treatment of the ground with a herbicide before placing the sand bed is generally
ineffective, since weeds tend to grow from seed deposited in the joints of the
paved surface.
4.10.7 Construction of edge restraints
Edige restraints must be constructed accurately to line and level. Precast concrete
kerbs are available in different forms: as garden mountable or barrier kerbs. The
kerbs must be secured in position with cast in situ concrete. Concrete kerbs can
also be laici in situ and special machinery is used to perform this task in a
continuous moving operation. Another form of edge restraint is the in situ placing
of a 1:3 cement and river sand mixture to form a 45 ° slope to secure the blocks
in position. Although this method is widely used, it is the most likely to fail. The
basic reason for its failure is that the edge of the concrete does not penetrate
deep enough into base material and no allowance is usually made for expansion.
This edge restraint should, if used, be cut through with a trowel at intervals of 1 m
to allow for movement and it should be let into the base material ai least 150 mm
deep. See figure 4.34.
4.10.8 Placing the sand bed
The sand bed is a high density sand laid loose on the prepared ground and
screeded off to a thickness of approximately 25 to 30 mm to receive paving blocks.
4.10.9 Laying of paving
The laying of paving can be summarised as follows: Determine the seiting-out line and attach a piece of
string to the fixed points.
Adjusi the string to forn a straighi line. The string should also follow the fa!!
of the proposed base.
BUILDING COMPONENT'S AND FINISHES
Lay the blocks tightly together on the area working, outwards from the setting
oui line.
Check squareness and levels every 10 rows.
Correct any creap by re-lining the pattern.
Compact ihe total area using a plate compactor.
Check for uneven and broken blocks, lift and relay.
Re-vibrate areas where disturbance took place.
Sweep fine dry sand over the surface to fill the joints completely.
Re-vibrate to compact sand into joints.
Traffic can use area immediately.
Note:
Edges butting against walls or
other structures need no further
restraintGarden or paved area
Precast concrete kerbBlocks
Sandbed
Mass concrete backing (1:5:5) cast in situ - edge restraint
Blocks
Garden
YK
Sandbed
Mass concrete (1:5:5) cast in situ - edge restraint
Precast concrete kerb - edge restraintGarden
Blocks
AL
SandbedWell-compacted fillGarden
Cast in situ concrete kerbing
(1:3,5:3,5 - cast in 2 m lengths)Blocks
Sandbed
Figure 4.34 Paving details
Ground
QUESTIONS FOR SELF-EVALUATION
i. Discuss the various types of doors and frames commonly used inbrickwork. Where applicable provide
sketches io illustrate. (30)
2. Provicie sketches to indicate the typical ironmongery used in
buildings.(25)
3.
4.
5.
6.
7.
8.
9.
10.
Make sketches to show typical details used in tiling and plastering. (15)
Make sections and describe three types of ceilings.
Provide sections to indicate glazing in wood, steel and aluininium
respectively.
Discuss the types and uses of paini.
(15)
(15)
(15)
Describe five types of wall paper.(10)
Discuss post and panel partitioning systems. Where applicable
provide sketches to illustrate.(15)
Discuss mastic asphalt roof coverings. Provide sketches to illustrate
flashing details.(10)
Briefly suinmarise the laying of bevelled-edige paving.
(10)
160
REFERENCES
Council for Scientific and Industrial Research. 1970. Combating the deteriorationoi building materials in
coastal areas. Proceedings of and NBRI Symposium
held in Durban. Publication 04700.
Council for Scientific and Industrial Research. 1978. A technical guide to goodhouse construction.
Pretoria: National Building Research Institute.
Council for Scientific and Inciustrial Research. 1970. Deterioration of materials incoastal areas.
Publication 70395.
King, H. & Everett, A. Components and Finishes. 1971. Batsford, London: Michell's Building Construction.
South African Bureau of Standards. Codes of Practice SABS 05Preservation treatment of timber.
South African Bureau of Standards. Codes of Praciice SABS 064 -Preparation of steel surfaces for
painting.
South African Bureau of Standards. Standard Specifications SABS 312 -Red-lead base primer for
structural steel.
Souih African Bureau of Standards. Standard Specifications SABS 630High-gloss enamel paint.
South African Bureau of Standards. Standarci Specifications SABS 633 -Emulsion paints for interior
decorative purposes.
Souih African Bureau of Standards. Standard Specifications SABS 634 –Emulsion paints for exterior use.
South African Bureau of Standards. Standard Specifications SABS 578 -Primers for wood for interior and
exterior use.
Souih African Bureau of Standards. Siandard Specifications SABS 681 -Undercoats for paint.
South African Bureau of Standards. Standard Specifications SABS 683 -Roof paints.
South African Bureau of Standards. Standard Specifications SABS 684 –Structural sieel paint.
South African Bureau of Standards. Standard Specifications SABS 723 -Wash primer (metal etch primer).
South African Bureau of Standards. Standard Specifications SABS 801 -Epoxy-tar paints.
South African Bureau of Standards. Standard Specifications SABS 912Calcium-plumbate primer.
South African Bureau of Standards. Standard Specifications SABS 940 -Emulsion paint for new galvanised
iron.
NOTES
CONTENTS
LEARNING OBJECTIVES
5.1
5.1.1
5.1.2
5.1.3
5.1.4
5.1.5
5.1.6
5.2
5.2.1
5.2.2
5.2.3
5.3
5.3.1
5.3.2
5.3.3
5.3.4.
5.3.5
5.3.5
5.3.7
5.3.8
5.3.9
5.3.10
5.3.11
5.3.12
PLUMBING, SANITARY FITTINGS AND DRAINLAYING
Hoi and cold water installations
Drainage in buildings
Drains below ground
Sanitary fittings
Sinks, wash-hand basins and baths
Rainwater disposal in buildings
ELECTRICITY, LIGHTING AND SECURITY
Electrical installations
Lighting and environmental control
Alarm and security systems
Appendix: SI-Units
AIR-CONDITIONING
Definition of heating, ventilation and air-conditioning
The need for air-conditioning
Psychrometry
Human comfort
Heat, heat sources and heai transier mechanisms in building
Refrigeration and the refrigeration cycle
Air-conditioning system classification
Ventilation and filtration
Ducting and fans
Air outlets and inlets
Refrigeration equipment
Heat pumps
5
PAGE
221
221
221
233
236
240
243
244
247
247
276
281
295
296
296
296
297
300
301
307
308
315
319
323
326
334
5.4
5.4.1
5.4.2
5.5
5.5.1
5.5.2
5.5.3
5.5.4
VOLUME 1
LIFTS AND ESCALATORS
Lifts
Escalators
MECHANICAL SYSTEMS
Pneumatic tube transport systems
Smoke detection and fire prevention
Central vacuum cleaning systems
Waste removal
QUESTIONS FOR SELF-EVALUATION
REFERENCES
335
336
345
348
348
349
353
355
358
LEARNING OBJECTIVES
The objectives of this module are to introduce the student to the following
building services: Plumbing and drainage systems
Electrical, lighting and security systemsAir-conditioning, lifts and escalators, and mechanical systems
After completion of this module ihe student should be able to perform a basic
evaluation of building services and contribute to decision-making when
systems are selected.
5.1 PLUMBING, SANITARY FITTINGS AND DRAINLAYING
5.1.1 Hot and cold water installations
Hot water supply
Circulation of water
Hot water systems in buildings make use of the changes which take
place when water is heated. The system should also be installed in
such a way that these properties of water are catered for.
When a quantity of water is heated it expands; when cooled it contracts.
The smaller the space a given mass of water occupies, the greater is the
density of the water. The greater the space the same mass of water
occupies, the less dense it will be. Cold water is thuis more dense than
hot water.
When ihe waier at the bottom of a vessel is heated, it will be forced to
the top of the vessel by the sinking of the colder and denser water from
above. If the heat is applied continuously to the bottom of the vessel,
the colder water will continuously flow down forcing the warmer water
upwards, producing what are known as convection currents.
The flow of waier thus produced is called circulation. Since it is due to
the action of the force of gravity, it is spoken of as gravity circulation,
called natural circulation, distinguishing it from circulation induced by a
pump, known as forced circulation.
li the water is warmed in a container and not in the hot water storage
vessel itself, it is called a boiler. The heated water is discharged into the
storage vessel, from which cold water then passes to the boiler trough
circulation pipes. This can be achieved through gravity or forced
circulation.
Bolling point of water
The temperature at which water boils varies with the pressure, but does
not increase in the same ratio as the pressure. Thus, water boils under
atmospheric pressure at sea-level at 100 °C. Under an additional pressure
of 350 kN/m2 at 147 °C and under a pressure of about 700 kid/m2 above
atmospheric pressure at 169 °C. This principle can be applied if water
with a higher temperature than 100 °C is required.
Expansion of water
Water, when heated from its maximum density (4 °C), to boiling poini,
increases in volume approximately 1 part in 23. That means every
23 litres becomes 24 litres when heated over that range of temperature.
This expansion has to be catered for in the design of hot water systems,
failing that, leaks and bursting can occur in the system.
Pices and valves
Pipes for conveying hot water are usually of galvanised steel or copper tube.
The smooth bore of these pipes does not lend itself io serious scale formation
in primary circulating pipes.
Copper is clean to use, does not rust and is neat in appearance. When
used in tube form, copper is light enough for easy handling and less fixing
support is required than for galvanised pipes.
Copper tube may be formed into bends, etc. quite easily, particularly if a
machine is used for this purpose. Galvanised steel pipes are neavier than
copper and have to be threaded for fitting and joining, requiring special fittings
such as elbows and T-pieces. It can, however, stand higher pressures and
robust handling.
The diameter of pipes to supply water depends on: the number and size of iaps and sanitary fittings
likely to be discharging
water in the same system at the same time,
ihe pressure (or head) of the water,
the length of tire pipe (friction losses occur in long lengths).
It is better to have the distributing pipes a little too large rather than a little too
small to prevent the annoyance of starvation of outlets (thai is, not delivering
a full stream of water at all outlets at the same ime).
Safety valves
These valves, designed to relieve pressure which build up in hot-water
insiallation are of two types: The dead weight type, where a washer is held againsi its seating by
weights which govern the pressure at which the valve opens to relieve
pressure (see figure 5.1).
The spring-loaded type, where a spring performs the same function as
the weights. The spring-loaced type is shown in figure 5.2. A screwcap is provided io adjust compression
on the spring, which in turn
determines the pressure at which the washer is lifted from its seating.
The cap is locked in position by a back-ut when the final adjustment
has been made.
Mixers
The combination of a hotand cold-water iap, enabling water to be delivered
through a common outlet, is called a mixer (mixing valve). The volume of
water let ihrough each tap governs the temperature of water discharged.
Figure 5.3 shows iypical mixers, which could have a swivel nozzle, which is a
pre-requisite for cual sinks but may also be used over single sinks or wash
hand basins to provide freer access to the sink or wash-hand basin by
swivelling the spout out of the way.
Valve
SECTION
Figure 5.1 Dead-weight valve
Cap
Set screws
Weights
Fit into hot
water cylinder
Screw-cap
SECTION
Figure 5.2 Spring-loaded valve
SK
SWIVEL MIXER
BATH MIXER WITH SHOWER
Spring
Washer on seating
Figure 5.3 Swivel mixers and bath mixers
A mixing valve with thermostatic control is available for showers whereby
the temperature of ihe water is increased progressively as ihe control knob
is advanced. The thermostatic device is sei to determine the inaximum
temperature to prevent accidental scalding.
Taps and valves
Taps and valves are made from brass which is cast in a mould and inachined
to the final produci, whereafter it is usually chrome-plated.
Taps work on the principle that a jumper (washer) is adjusted up or down iby
a tap-handle which has a screw-spindle. When the tap is fully open, the
spindle lifts the jumper to the maximum height, opening ihe tap for the
maximum ilow of water. By turning the jumper all the way down, it shuts off
the water. The jumper (washer) is made of hard neoprene, about 3 mm thick,
which fits onto a round smooth seat when the water is shut off.
A gate valve (stopcock) works on the same principle as an ordinary tap but
the neoprene washer is replaced by a brass sluice which closes the waterflow
off by tightly fitting onto a brass seat. Gate valves can withstand substantially
more pressure than ordinary taps and are thus fitted into pipelines to shut
off the water supply to sections of a system when required, usually for
maintenance purposes. Gate valves are nighly machined and not intended
for daily use.
In-line ball stopcocks are used for the same reason as gate valves, but has
no handle. It is operated by using a screwdriver to change the position of
the ball “jumper' to open or closed. Figure 5.4 shows details of taps and
valves.
Electric water heaters
Because the heat derived from electricity is transferred to the water by direct
contact through an immersed heating element, very little electricity waste
occurs. Electrical heaters have a thermostai which keeps the water heated
to a given temperature. When electric heaters are employed, a hoi water
system needs to consist only of a storage vessel (geyser) fed with cold water,
In large installations, such as in hospitals and big office biocks, a separate
boiler and storage vessel are used.
The immersion heater elemeni and thermostai are mounted near the bottom
of the geyser and the entire contents are heated as a result of gravity
circulation.
The heating power oí immersion heaters is expressed in kilowatts. The power
rating would be selected to fulfil the requiremenis in respect of:
VOLUME 1
size of hot water geyser, determined by,
rate of utilisation of hot water (draw-off frequency);
permissible recovery period (from cold to hot again);
inlet water temperature.
Spindle
Gland
Packing
Jumper
Washer
Spindle
Gland
Packing
Jumper
Washer
Spindle
Gland
Packing
Sluice
Outlet
PISTAMANNS
BIB TAP
Outlet
PILLAR TAP
GATE VALVE (STOPCOCK)
Nickel-plated brass ball
with hole through centre.
Quarter turn with screwdriver shuts off flow
Neoprene seal
Handle
Water
inlet
(Supply)
Handle
Water
inlet
(Supply)
Handle
Water
inlet or outlet
if not "one-way"
Neoprene seal
INLINE BALL STOP
Figure 5.4 Taps and valves
Water inlet
or outlet
if not "one-way"
An approximate proportion for domestic installations is 2 to 4 kw (kilowatts)
per 100 litres of storage capacity. For commercial, industrial, hospital, etc.
use, the size of the installation is determined by the size of ihe building and
its facilities. To ensure economy it is important that the geyser (and storage
vessel) be insulaied against heat loss.
Figure 5.5 shows a iypical electrical geyser insiallation.
400 kPa safety valveHot water outlet
3 Mounting bracketsElectrical cover plate
Draincock and cold water inlet
House water station. Installation
at ground level where cold
water supply is introduced/
plumbed into house, including
expansion valve
2 Bal-o-stopIn-line strainer
Vacuum breaker
Balanced cold water feed
Figure 5.5a Typical electric geyser installation: horizontalinstallation
400 kPa safety valve
2 Hot water outletWalt brackets
Electrical cover plate
Draincock and cold water inlet
Masterflo I pressure control valve (expansionvalve)
9 Balanced cold water feedwith vacuum breaker
D Isolating valveVacuum breaker
Figure 5.5b Typical electric geyser installation: verticalinstallation
Gas water heaters
Gas water heaters do not store heated water but heats it within the appliance
prior to discharging it ihrough a iap. When a hot watertap is opened, water
flows and its action upon a diaphragm brings a burner into operation. The
gas jets in the burner are ignited by a pilot fiame, heating the water for as
long as the tap is open.
Hot water distribution in simple buildings
Gold feed pipes
The cold water feed pipe for a hot water system should be of adequate
size to ensure the presence or water at all outlets being used at the same
time. The cold-feed pipe should never be smaller ian 20 mm internai
diameter and no branches inay be taken from it for other purposes as it
can cause a waterhaminer in the pipes. A gate valve or ball stop is fitted
in ihe pipe before ii enters the geyser. See figure 5.6. Boiler systems
are specially designed in each instance.
Draw-off pipes
These should not be less than 20 mm nominal bore to baths and 12 mm
nominal bore to wash hand basins and sinks. Resistance to the flow of
not water should be kept to a minimum by avoiding unnecessary changes
of direction. A gradient of at least 1 in 120 should be maintained on
draw-off pipes to prevent air pockets which can cause water hammers.
Expansion and pressurs
All hot water systems should be provideci with a means of releasing
pressure build-up due to expansion as the water is heated. This is
achieved by fitting an expansion valve in the cold water supply line.
This valve compensates for expansion due to ihe heating of the water
by allowing the excess (expandeci) water to "drip" out of the system as
free water.
Combination expansion and pressure valves are in common use. The
pressure valve ensures stable pressure in both the hot and cold water
supply and is particularly valuable as it provides an even flow through
mixers. Shower mixers oniy provide water at a constant temperature
when expansion/pressure valves are installed.
Water supply in simple buildings
Water distribution (figure 5.6) is normally through galvanised steel, copper or
polyvinyl chlorine (PVC) pipes (the latter is not suitable for hot water).
The main cold water supply is provided by the local authority through a water
supply meter followed by a stop valve. The premises are usually fed with a
20 mm or 25 mm supply taken off the local authority mains on the boundary
of the stand for small buildings, while a calculated size is used for large
buildings.
ITEM
qoy
HIGH PRESSURE INSTALLATION
Expansion relief valve and vacuum breaker
Emergency safety valve
Pressure control vale
Strainer
Inline ball stop
Cold water supply
Hot water supply
Point of service
SYMBOL
h
o
Figure 5.6 Hot and cold water distribution in small buildings
A building can be supplied with cold water through one or more points of
entry into the building. At each point of entry a gate valve (stopcock) is
installeci in order to close off the supply in case of leaks or maintenance
work. Garden taps are branched off the main supply outside the buildings
at convenieni places.
Hot and cold water distribution in high-rise buildings
High level storage cistern
serving upper floors
Fire brigade
inlet
Street main
Boosting
installation
Fire
hydrants
Bypass
Air/water pressure vessel
A
귀
OMI
I.
General
distribution
Pump
installation
Non-return valve
Water meter
To sprinkler
installation
Boosted
pressure
zone
Cistern
pressure
zone
Mains
pressure
zone
Figure 5.7a Cold water distribution in high-rise buildings(Clark, 1983:42)
Service pipe to
individual heaters
Street: main
supply
Cold water
storage cistern
Secondary return
Cold water
storage cisternIndividual waterheaters
Basin Bath
FEE
LOCAL HOT WATER SUPPLY
Sink
ri
Street; main supplyHot water storage cylinder
Basin Bath
中山
Hot water circulates
round secondary
flow and return
Secondary flow
Boiler
CENTRAL HOT WATER STORAGE AND SUPPLY
Figure 5.7b Hot water distribution in high-rise buildings(Clark, 1983:45)
5.1.2 Drainage in buildings
Ghoice of systems
The choice of systein depends on the nature of the building and the grouping
of the fittings. The pipes may be of cast iron, polyvinyl chloride (PVC),
galvanised steel or copper. The following three systems are commonly used:
Two-pipe system
The soil sanitary fittings in this system, figure 5.8, discharge into a soil
pipe, then directly into the drain without passing through a gully trap. The
toilets (WCs) are fitteci with a ventilation pipe. This pipe's main function
is not to "ventilate" the pipe system as that serves no purpose, but to
prohibit a vacuum being created by the run dowr.. A vacuum would slow
the flow of soilwater down and can lead to blockages.
The waste fittings (wasin-hand basins, sinks, etc.) connect to a separate
waste pipe, which passes through a gully trap before entering the manhole
and drain. A ventilation pipe is also provided. The two-pipe system is
very expensive and has fallen into disuse in new buildings as a result.
One-pipe system
This system, shown in figure 5.9, is particularly suitable for multi-storey
buildings where the appliances are similar on each floor. All soil and
waste fittings are arranged to discharge into a common waste pipe. The
traps on each of the waste fittings musi be of the deep-seal variety (at
least 75 mm seal), to counter the increased negative pressures caused
by the down flow, with a ventilation pipe provided.
Single stack system
After considerable experimental work, this syste. n, illusirated in figure 5.10,
was devised as a simple and more economical alternative than the
one-pipe system whereby the need for ventilating pipes was eliminated
subject to the following conditions:
The appliances must be grouped together.
Branch connections should be no more than 25 mm radius on invert,
as shown in figure 5.11 (a UPVC system). The gradient on branch connections must be carefully
calculated
In figure 5.11 all the soil and waste fiitings discharge into one pipe. The
joints in this system are by spicot and sockets. The socket is provided
with a recess to receive a synthetic rubber "D"-ring seal which is inserted
just before the spigot is pushed into the socket. The internal diameter
of the downpipe is 100 mm.
Ventilation pipeSoil pipe
Al
WC
wc
WC
1B
1
1
1
1
1
Bath Basin 1
Drain
Sink
Basin
E
Figure 5.8 Two-pipe drainage system
Soil pipe
WC
WC
AB
Bath
Drain
Sink
Basin
Basin
**
Figure 5.9 One-pipe drainage system
Ventilation pipe
Waste pipe
Gulley trap
Man
Vent pipe
WC
WC
AL
Bath
САНС
Drain
Basin
Sink
Soil and vent pipe
B
D:
Figure 5.10 Single-stack drainage system
Access to pipe work
Access should be provided to enable all pipework to be cleaned and tested.
Soil arci waste pipes should have removable access covers fitted ai strategic
points so that obstructions may be removed and to allow testing to be carried
oui. A wire balloon or one-way air inlet cap is provided at the top of ventilation
pipes to prevent ihe entry of foreign matter such as birds' nests.
Wire balloon
OR
Figure 5.11 Single-stack UPVC drainage system
Vent valve
5.1.3 Drains below ground
Underground drainage systems transport waste and soil water irom tive building
to ihe local authority main drain which is normally under the street or adjacent to
it. The local authority main drain eventually terminates at sewerage disposal wories
where water purification takes place.
The drainage on a typical building site will consist of eniry points, pipe runs, bends,
junctions, cleaning and inspection eyes and vent pipes. It is important thai all flow
BUII. DING SERVICES
in cirain pipes is such that no air is discharged into buildings and ihai the flow in
the drain is at such a rate (as a result of the fall in the pipe), thai no solids are left
siancing. Typical drainage pipe sizes are 100 mm and 150 mm internal diameter.
A gradient sieeper than 1:6 or flaiter than 1:50 should be avoided as it causes
blockages. Ramps may however be used when a steep, short fall over a distance
of maximum 2 metres is inevitable.
The furthest point (highest point) of the drain should always be ventilated by means
of a ventilation pipe (ventpipe) which extends well above roof level. If the ventpipe
ends below the roof line, it inust be fitted with an air iniet cap which prevents drain
smells to escape, but allows air into the drain to prevent vacuums and blockages.
Drains shoulci be laid in siraight rins with proper bends (various degrees available)
where a change in direction is required.
Where drains conneci at junctions (various degrees available), as well as at ramps,
rodding eyes (normally 45° out to the surface) are required. Rodding eyes must
also be provided ai the upper extremity of the drain and at each change in
clirection to facilitate the cleaning of every straight length of pipe.
Access points musi be provided at all junctions and bends above and below ground
in order that they may be opened to clear blockages. ivianholes (or inspection
chambers) are costly items, built out of bricks or pre-cast concrete rings packed
on top of each other. ivianholes are provided in drainage systems which are
subjeci to high volumes and/or are likely to get blocked when very long drains
occur.
Various types of pipes (materials) are available with different jointing methods.
When active sol conditions are experienced a flexible type of pipe and/or joint is
used. Clay pipes are well tried and commonly used. Other materials often used
are cast iron, pitch fibre, asbestos ceineni and UPVC. The cost of pipes as well
as the cost of laying varies and the material used must be carefully considered
for each application. See figure 5.12 showing the general requirements for drains
below ground.
Where a local authoriy does not supply drainage mains (srnall settlemenis, small
holdings, faims, etc.) the sewerage disposal normally takes place by using a septic
tank and French drain. The remainder of the drainage systein remains unaltered.
Septic tanks can be constructed or are available as patented asbestos, fibreglass
or UPVC units. The principle on which it works however remains the same.
The sewerage is allowed to stand in the tank, sludge setties on top of the water
where it is broken down by anaerobic bacteria. Clear liquid overflows to the French
drain via an overflow pipe collecting the liquid from the botion of the iank as new
sewerage flow enters the septic tank. The overflow inio the French drain seeps
into the surrounding ground. Some household detergents and cleaning inaterials
effeci the bacteria to the detriment of the system and should be used selectively:
See figure 5.13.
Rodding eye at upper extremity of drain
for access within 1.5 m of upper extremity
One gulley per installation for discharge of
ground floor waste fittings
Point of entry
Drains falt: max 1:6
min 1:60
Drains to be minimum of 450 mm
below ground cover or paving
Rodding eyes at max 25 m
intervals
Branch drain meets
main drain 45°
1E
LA sewer
NOTES:
1E
Property boundary
1E
1E
1E
1. Manholes may be provided in place of rodding eyes
2. Access at all junctions
All drainage installations - at least one
vent pipe - same diameter as drain - at head of drain
Point of entry
Rodding eye required for branch drain longer
than 3 m
Vent pipe required for branch drain longer
than 6 m
Access required within 1,5 m of upper extremity
1E
Point of entry
Drains under buildings - avoid if possible.
Avoid change of direction or grade
Prevent transfer of loads to pipe. Access for
inspection required at either end. (1E)
Ramp at 45° - where fall exceeds 1:6
provide rodding eye
Install rodding eye within 1,5 m of sewer
connection.
Access for inspection eye within 1,5 m of sewer
connection.
Figure 5.12 General requirements for drains below ground(Clark, 1983:118)
Inlet
from
building
1 000 mm
PLAN OF SEPTIC TANK
Precast reinforced concrete slabs or
solid reinforced concrete slab with
access to compartments, inlet and outlet
Gas
75 mm
Concrete
floor
225 mm brick or
100 mm concrete
A
1,00 m
-1,75 m
Liquid level
A = not more than 0.2 x liquid depth
B = 0,4 liquid depth
ES
150 mm Soil cover
Air space
B
150 mm x 150 mm
opening
1,00 m
112 mm brick
(this wall may
be omitted)
LONGITUDINAL SECTION X-X OF SEPTIC TANK
Figure 5.13a In situ constructed septic tank
Outlet
to French
drain
225 mm brick
or 100 mm
concrete
Prefabricated septic tank
A double chamber ribbed tank manufactured from materials as moulded
polyethylene that will withsiand ground pressure, is freely available in the
market. The ribbed walls eliminate the necessity for a heavily constructed
concrete siab being placed over the top of the tank.
Waste Water
MH
+200-*
400
GROUND PLAN: TOILET, SEPTIC TANK AND FRENCH DRAIN
NGL
River sand
HOOLT
+ 1000
-400Perforated
piping
Soil
Shade cloth
Granular
20-100 mm
well mixed
CROSS-SECTION OF FRENCH DRAIN X-X
Figure 5.13b French drain system
*100+
-400
As an alternative to septic tanks and French drains, use can be made of
conservancy tanks from where the sewerage is emptied by a special suction
vehicle. This is a costly option and should only be used when septic tanks and
French drains are not advisable due to the im ous nature of the soil.
5.1.4 Sanitary fittings
Water closets (ioilcte)
Waier closets (WCs) are usually a glazed, very fine clay produci of exceptional
sirength and easy to clean. Two main iypes are used:
Pedestal water closet
This is the most popular type of WC, shown in figure 5.14.
The flushing rim is shown at (A), the inlet receiving the flush pipe at (B)
and the seal at (C). Pans may be supplied with either an S-irap or a
P-trap to suit the desired position. Figure 5.14 shows a P-trap, with a S-trap
indicaied by the cotted portion. The outlet of a P-trap may be obtained
discharging to the back, left or right. The purpose of the trap is to prevent
odours from the drainage system to enter the building via the WC.
A
to
Figure 5.14 Pedestal water closet
B
Double-trap siphonic water closet
Figure 5.15 shows a section of a pan in conjunction with a flushing
cistern as a complete WC suite. This type is more expensive than the
pedestal wash-down closet, but it is much quieter and a better evacuation
of the contents of the trap occurs due to the double trap. When flushing,
the air pocket between the two trays is compressed, expanding fast
when the second trap overflows under this pressure, causing a vacuum
which sucks the first trap clean.
Figure 5.15 Double trap siphonic water closet
Urinals and bidets
Urinals are commonly used in men's cloak rooms in non-residential buildings.
If they are properly designed and fitted, urinals contribute considerably to
the number of users that can be served in a given period. The overall cost
of a urinal is also considerably lower than the cost of a lockable ioilet
facility. It is fixed to the sanitary pipework on the same basis as a toilet.
See figure 5.16. It is important that urinals are regularly sanitised,
particularly in high use areas.
Bidets are fitted in residential accommodation and are installed io facilitate
personal hygiene. They are fitted with cold and hot water supply, through a
Imixer with an adjustable nozzle. The drainage pipework to a bidet is the
same as for a toilet. See figure 5.17.
ELEVATION
Floor line
PLAN
Water
inlet
SECTION
Figure 5.16 Urinals
Water
inlet
FLOOR URINALS
Outlet
Floor line
Outlet
0004
Step
SECTION
Channel
ELEVATION
09
WALL-MOUNTED URINALS
Figure 5.17 Bidet
5.1.5 Sinks, wash-hand basins and baths
Sinks
Sinks are of various designs and materials according to the purpose for winich
they are used.
Stainless sieel and acrylic (reinforced with fibreglass) are commonly used.
Sinks may be supported by cupboards, pedestals, metal legs, or brackets.
As there is risk of water spillage, the surrounding area of floors and walls
should be tiled or of a material wirich is water resistant. All waste outlets are
fitted with a trap and a grating to prevent the entry of solid matter. A typical
kitchen sink unit is shown in figure 5.18. The cupboards are designed to
enclose the pipework below the sink and to make use of the space below
the sink for storage. The illustration shows a single sink unit with drip boards.
Double bowls are also in common use.
Wash-hand basins (whb)
A pedestal supported wasi-hand basin in vitreous china is shown in
figure 5.18. The pedestal is of the same material and colour as the basin.
Wash-hand basins can be fitied with a variety of taps anci plugs. Washhand basins can also be fitted into
cupboard tops or concrete vaniiy slabs.
Perspex wash-hand basins are fairly common and usually fitted in factory
made bathroom cupboards.
Baths
Baths used io be mainly of cast iron or pressed steel, vitreous-enamelled
internally. Perspex baths are however now virtually the only iype used.
Access to pipework and fittings musi be given on the sicie of ihe baih through
ihe brick wall supporting the bath. See figure 5.18a.
Sink
Washhand
basin
Bath
Waste water from sanitary
fitting
5
To drain
system
Typical trap to prevent odours from drainage
system to enter building - fitted to all
sanitary fitting outlets
Access opening
with cover
Figure 5.18a Sinks, wash-hand basins and baths
5.1.6 Rainwater disposal in buildings
Rainwater on buildings is disposed of by using guttering ai roof level, rainwater
downpipes and a disposal system. Guitering is normally fitted at roof level where an overhang is
provided is
usually made of galvanised sieel or aluminium. In large buildings, where
ilat roofs occur guiters are not used and the water is collected by creating
falls in the roof screed, at a "full-bore" outlet (a funnel inlet with metal bull
grating over) on top of a downpipe.
Downpipes fitted with brackeis on the ouiside of the buildirig are usually made
of galvanised steel sheeting or aluminium. In high-rise buildings the
downpipes are usually accommodated in the centre of big coluinns or in
pipeshaits.
See figure 5.18b and 5. i8c showing typical cletails.
HH
L
M
к
Roof overhang
E
A
B
Detail snit
A = 38 X 114 mm S. A. PINE RAFTER
B = 50 X 76 mm S. A. PINE TILTER BATTEN
C = 12 X 150 mm ASBESTOS CEMENT FACING
D = 87 X 125 mm GULLY SHEET METAL GUTTER
E = HALF BRICK BEAM FILLING
F = 50 X 76 mm S. A. PINE ROOFPURLIN
G 0.6 OF 0.8 mm SHEET METAL ROOF COVERING
H = 38 X 1144 mm S. P. PINE TIE BEAM
1 = ONE 10 mm ROOF TRUSS BOLT 87 mm long
WITH NUT AND WASHER AND 3 VIRE NAILS
J = 38 x 114 mm ORX76 mm S. A. PINE WALLPLATEBEDDED IN CEMENT DAGHA
K = 2 x 4 mm 8 CALV. WIRE ROOF ANKER TIEDAND NAILED TO ROOF TIMBERS
L = 280 mm CAVITY WALL
M = 10 min 8 x 130 mm LONG STEEL ROOF ANCOR PIN
N - STANDARD PRECAST CONCRETE RAIN WATERCHANNEL:
0 = SHOE
P = 80 mm 8 OF 75 x 64 mm DOWN PIPE
Q = EAYES OFFSET
Figure 5.18b Gutter, downpipe, shoe and rainwater channel
38x64mm
GRP edge
trim
Plywood
gutter
base
Timber fascia
19 mm
asphalt
Internal
clamping ring
Cast iron
outlet pipe
DPC
Outlet
component
GRP
outlet
flange
GRP
extension
piece
UPVC
rainwater
pipe
Metal
grating
,D
UPVC
gravel
guard
WW
Sheathingfelt
concrete
sub-structure
Cast iron rainwater
pipe with spigot joint
Lead or bituminousfelt cavity tray
Stone or
concrete coping
Felt tuckedMetal cover
in 25 mm
minimumflashing
150 mm
minimum
Vapour :
barrier
2
Insulation
Roof
substructure
WNNNNNNINN
Roof
deck
Built-up
bituminous
felt roofing
Fixing nut
Grating
Lock nut
Clamping device
Arms for bolting
clamping coně
Fixing hook bolt
Metal head
Anchor bar
for hook bolt
Outlet pipe
Sheathing
150 mm Metalfelt
minimum grating
19 mminternal
asphalt clamping ing
Cast iron
outlet pipe
Figure 5.18C Rainwater outlet to flat roofs
Concrete
substructure
Cast iron rainwater
pipe with spigot joint
The disposal system is critical as downpipes often have to ium into a disposai
pipe or channel, ofien blocking at that point as debris collects in the bottom
of downpipes. It is advisable to have a visible (inspectable) exit point at the
bottom to facilitate inspection and easy maintenar. ce.
5.2 ELECTRICITY, LIGHTING AND SECURITY
5.2.1 Electrical installations
(a) Units of electricity
Unit of force
The unit of force is the Newton (N).
A Nawion is the force that must be applied to a mass of 1 kg to cause an
acceleration of 1 m/s2
The force of F Newtons that will cause an acceleration of a in/s2 of a mass
of m kilogram is therefore expressed as:
(N)
=
(kg)
a
(m/s2)
Unit of energy
The unit of energy is the joulo.
A joule is the work done by a force of 1 N when it is applied for a distance
of 1 m in the direction of the force.
Thereiore work performed in joules = F (N) * s (m).
Unit of power
Power is the rate at which work is performed. Power is expressed as an
energy-unit per time-unit, i. e. as joule/second.
The unit of power is the watt (W) (in honour of James Watt - a pioneer in
the clevelopment of the steam engine).
A watt is the unit power required to perform work of 1 joule in one second.
A larger unit of power is the kilowatt, which is equal to 1 000 watts.
Because power (wati) is equal to energy/time, it follows ihat energy can also
be expressed as power x time, for example 1 joule = ï watt x 1 second.
Because ihe joule is inconveniently small for commercial purposes, the unit
of kilowatt-hour (kWh) is rather used:
(D)
NB)
1 Kilowatt-hour = 1 000 watt-hours= 1 000 X 3 600 watt-seconds
= 3 600 000 joule3,6 x 106 joule (or 3,6 MJ)
Note: A Kilowatt-hour is a unii oí energy, while a kilowatt is a unit of power.
=
Electrical quantity
The amount of electrical charge, indicated by the symbol O (for “Quantity'),
is measured in coulomb.
One coulomb is the amount of electrical charge that is carried by 6,24 x 1018
electrons. One electron therefore has a charge of about 0,16 of a inillionth
of a millionth of a millionth coulomb!
As Sl-unit, the coulomb is defined as the amount of electricity that moves
past a given point in a circuit if a current of 1 ampere flows for 1 second:
1 coulomb = 1 simpore x 1 second
In general:
Q (coulombs) = I (ampere) xt (seconds)
Electrical current
By an electrical current (indicated by the symbol I) is meant the rate at which
electricity flows past a given point. It can be compared with the flow of
water through a pipe.
The unit for measuring electrical current is the ampere (A), sometimes
called amps for short. (The unit is named after the pioneer physicist
André Marie Ampère.)
One ampere indicates a rate of flow of 1 coulomb per second:
1 ampere - 1 coulomb/1 second
In general:
I=
QA,
i. e. electrical current = the amount of electricity that flows past a certain
point in one time-unit, analogous to a stream of water which is the amount
of water (say litres) that flows pasi a certain point per time-unit (second).
Electrical voltage
In an electrical circuit electrical energy is converted to other forms of energy.
A lightbulb converts electrical energy to heat and light, and a electrical motor
converts electrical energy to mechanical energy. Such conversions of energy
form the basis of the definition of the term potential difference.
The potential difference between two points in a circuit is the amount of
electrical energy that is converted to other forms of energy when a unit
charge moves from one point to another.
The unit of potential difference is the voit (V) (named after an early pioneer
in electricity, the Italian physicist Alessardro Volta).
A volt is the poteniial difference between two points in a circuit in which
1 joule electrical energy is converted when i coulomb flows from one point
to another.
The elecirical voltage (or electrical pressure) is the electrical potential which
causes a curreni to flow in a conductor. It is indicated by the symbol E
(from electromotive force) or V (from "Voltage”). It can be compared with
the pressure in water pipes.
Like any other measurement of pressure, the electrical voltage is measured
beiween two points (e. g. between two points in an electrical circuit).
If a charge of Q (in coulombs) flows in a part of a circuit over which there is
a potential difference of V (in volts), ihe energy change W (in joules) will be
given by W = Q. V.
If Q is in the form of a current I (in amperes) ihat flows for a time t (in seconds),
then
Q = I. t and W = Lt. V
Electrical resistance
Like any other flow or novement, the flow of an electrical current is subject
to friction. Electrical resistance is the resistance againsi the flow of power
in a conductor. It is comparable to the friction in a mechanism. Electrical
resistance is indicated by the symbol R (“Resistance"). The capital R is used
to indicate the total resistance and Ry, Rz, etc., are used to incicate individual
resistances.
The unit of electrical resistance is the ohm, which is indicated by ihe symbol
12 (the Greek letter omega). (The name ohm is in honour of another electrical
pioneer, the German physicist Georg Simon Chin).
(D
1 Ohm is the resistance of a conductor in which an electrical current of
1 ampère flows if a potential difference of 1 volt is applied over the conductor.
Examples of substances with little resistance to electricity and therefore good
conductors, are copper, silver, gold, aluminium and carbon graphite, to mention
only a few. Silver is the best conductor, but copper is the most commonly
used substance for wiring because it combines a low resistance with
reasonable cost. Although the resistance of aluminium is nearly twice that
of copper, its density is only about a third of that of copper. The ratio of currentcarrying capacity to
weight of aluminium is therefore larger than that of copper.
This explains why aluminium is commonly used in overhead powerlines
(aluminium conductors are wound around a core of steel wires, to ensure
the necessary strength).
Other substances, like rubber, most types of plastic, glass, porcelain, oil, dry
air and asbestos, have high resistances. Such substances are useful as
electrical insulators. Wire conductors are usually made of copper or aluminium,
covered by rubber and thermoplastic. No substance has a zero resistance
or an infinitely high resistance - there does not exist something like a perfecî
conductor of a perfect insulator. Also note that the insulation capacity of
fibre-like substances like paper and cotton is dependent upon the amount of
moisture it contains.
The first factor that delerinines the resistance of a conductor, is therefore the
substance of the conductor.
The resistance of a conductor is also directly proportional to its length I and
inversely propoitional to its cross-sectional area A. The longer the conductor,
the higher is its resistance, and the thicker the conductor, the smaller its
resistance.
The resistance of a conductor is also proportional to its temperature. The
resistance of a copper conductor, for example, is about 3,9% higher at a
temperature of 30 °C ihan at a temperature of 20 °C.
Ohm's Law
The German physicisi Georg Ohm discovered a basic relationship between
current, voitage and resisiance, namely that current is directly proportional
to voltage and indirectly proportional to resistance.
This relationship is expressed in algebraic form as follows:
where
and
! = V/R
i = current (A)voliage (V)
R = resistance (12)
=
From ihis simple formula it also follows of course thai
and
R = VI
V = I. R
If a circuit with a resistance of R ohms carries a curreni of I ampere, the
potential difference (volt) over the circuit is therefore expressed as V = I. R
or E = I. R.
Electrical power
Power (whether mechanical or electrical) is the rate at which energy is
converted from one form to another form. The symbol for electrical power
is P ("Power"). Power is also sometimes called (electrical) power consumption
(do not, however, confuse ihe ierm "electrical power" with mechanical power).
If the potential difference over an appliance is V and the current that flows
through the appliance is I, the electrical energy that is converied by the
appliance in time t is equal to
W = I. i. V
The power of the appliance is p =
W
I. t. Vt
= I. V
Power (P) is therefore the product of the voltage (V) and the current (1):
P = V XI Watt
From this formula it also, of course, follows that
V = PAI
and I =PN
For resisting loads ihe power is the effective voliage multiplied with the
effective current. We shall see later that the electrical power for non-resisting
loads like a motor, is equal to the effective current inultiplied with the effective
voltage, and multiplied with a power facior.
Example 1:
(a) Calculate the electrical current I which is consumed if a 100 W lap isconnected over a 230 V supply.
Solution:
From the data: I = ?; P = 100 W; V = 230 VElectrical power P = V. I, therefore I = PN = 100/230 A= 0,435 A
(b) Also calculate the resistance of the filameni.
Solution:
From V = I. R it follows thatR = VI
= 230 V/(0,435 A)52922
Exampic 2:
If the specifications of an electrical vacuum cleaner inciicate that it is suitable
for 1 500 W and thai it must be connected to a 250 V supply, what iype of
socket outlei will you recommend? Motivate your answer.
Solution:
Given: P = 1 500 W; V = 250 V; I = ?
From P = V. I it follows that I = PN(1 500)/250 A6A
With a safety factor of 2, 1 = 12 ampère. A 15 A socket-outlet is therefore
sufficient.
Example 3:
In a factory there are 40 lamps of 100 W each, 35 lamps of 200 W each
and 6 lamps of 500 W each, as well as electrical motors that consume 15
kW and electrical fans that consume 25 kW. What is the maximum current
that will be consumed if there is a 240 V supply? What will be the cost of
electrical energy at 3,5c/kWh for a 44-hour working week?
Solution:
(a) P = [40(100) + 35(200) + 6(500) + 15 000 + 25 000] W(4 000 + 7 000 + 3000 + 15 000 + 25 000) W
= 54 000 W
From P = V. I it follows that I = PN = 54 000/240 A = 225 A
(b) Electrical power PEnergy consumption
iherefore cost
Example 4:
= 54 000 W = 54 kW
= 54 x 44 kWh
= 54 x 44 x 3,5c = R83,16
li a voltmeter has a resistance of 30, caiculate the current and the power
absorbed if ii is connected to a 460 V supply.
Solution:
(a) I = V/R = 460/30 A = 15,33 A
(b) Power P = V2/R(460)2/30 watt
= 211 500/30 watt7,053 kW
=
Power and Ohm's Law
From Ohin's Law (V = I. R) and from the definition of power (P = V. I) the
following relationships follow:
P= 12. R
P = V2/R
R = P.12
R = V2/P
li is not worth it to iry to memorise the relationships – it is easier to deduce
them from V=LR and P = V.1.
Example 5:
Determine the current in a circuit if the power consumption through a
resistance of 4,7 K2 is 350 inW.
Solution:
From the data: R=4700 12; P = 0,35 W; i = ?
From 12 P/R ii follows that I = V0,35/4 700 A
=
= 8,63 mA
Example 6:
An electrical circuit wiih a resistance of 2,5 consumes 100 kW. Calculate
the supply voltage.
Solution:
V2 = P. R
therefore V = V100 000 x 2,5 V = 500 V
Example ?:
Calculate the power consumption and the resistance of a 240 V filament
lamp if there is a current of 1,5 A through the filament.
Solution:
P = V. I = 240 V X 1,5 A = 360 W
From Chm's Law: R = V/I = 240/1,5 = 160 12
(NB
Summary
Property
amount
current
voltage
resistance
power
energy
Quantity
amount
power
Symboi
I
V or E
work (energy)
R
0.3
voltage (Ohm's Law)
For direct current:
Serie
R=
V=
I
Ry + Rg + R3
V1 + V2 + V3
!1 = 72 = 13
(b) Alternating current circuits
Unit
coulomb
ampere
Parallel
volt
ohin
watt
joule
Abbreviation
Formula
Q = I. t
P = V. I
W = P. t
V = I. R
1/R = i/R4 + 1/R2 + 1/R3V4 = V2 = V2
I !4 + 12 + 13
с
А
V
12
J
Effect of inductance
When an electrical current ilows through a conciucior, a inagnetic field is
created around ihe conductor. The direction of the field is determined by
Fleming's right hand rule. When the conductor is wound in the forn of a
coil, the magnetic field is concentrated in a smaller area and it becomes
much sironger. The strength of the magnetic field is a function of the current
strength and the number of windings in the coil.
With direct current the magnetic field remains constant after the current has
reached its final sirength, and the magnetic field does not have any further
effect on the current. In the case of alternating current, however, the current
direction and iherefore also the magnetic field changes continuously. The
changing field induces a voltage that works against the change in the currenta process known as selfinductance or, more briefly, induciance.
With self-inductance the induced electromotive force (emf) in the conductor
is proportional to the rate of change in the magnetic field, in other words
proportional to the rate of change of the current in the conductor. The induced
emf is countering the applieci voltage continuously. The effect of the induced
em can be considered as an additional resistance in the circuit - the so-called
inciuctive resistance, indicated with the symbol XL. The induced resistance
is directly proportional to frequency, but can be considered as a constant in
the case of the fixed frequency of the alternating current. In an electrical
circuit, the combined effect of the resistance as well as ihe inductive resistance
is known as the impaciance (7). The calculation of the impedance of an
electrical circuit is dealt with in the next paragraph.
All electrical equipment thai contains windings - generators, transformers,
electrical motors, discharge lamps, etc. -- exhibit the property of inductive
resistance. in all these cases we therefore refer to the impedance of the
circuit, instead of to the resistance of the circuit.
Impedance
impeciance, Z, is tire total resistance against the flow of a current in an
alternaiing curreni circuit. Ohm's Law for alternating currenis now becomes:
Z=EN
where E and I are the rms (root mean square) values of voltage and curreni,
and Z = impeclance in ohms.
The voltage drop I. R is in phase with the current. Because the voliage crop
I. XL is, however, 90° before the current, ihe resistances R and XL cannot
simply be summes. The inductive resistance X_ musi be adjusted with a
facior j, so thai
R+JXLVR2 + (XL)2
In other words, the resistances R and Xų are summed vectoriaily.
z=
Example 8:
If E= 120V, R = 822, and XL = 6.22, calculate ihe value of the current I.
Solution:
Z = R + jXL
Power factor
= VR2 + XL2
V82 + 62 = 1012
Significant savings can be made in the installation of power factor correctio?
equipmeni. This can reduce the maximum demand portion of the monthly
electricity account (which may comprise up to 50% of total account) by up
to 20%. Because tenants normally pay for electricity consumed, property
owners are often not concemed as to how much electricity is consumed.
This is a short-sighted attitude because in the long term nigher rentals can
be achieved in buildings with low electrical costs than in expensive electrical
cost centres.
If the current and the voltage are not in phase (as is the case witin an inductive
circuit), the real power (power consumption) is less than the apparent power.
Instead of the expression P = V. I (the apparent power), the real power is
now
P=
VL. PL cos e
in other worcis kW KVA cos
wherekW = real power,
KVA = apparent power
and cos e is ihe so-called power factor (Pi)
This expression is therefore deduced by vectorial summation from the socalled power triangle. The
power factor is the ratio between the real power
and the apparent power, and can be expressed as decimal (e. g. 0,90) or as
a percentage (90%).
As o increases, cos e decreases, e. g.
3 = 0º,= 1
0 = 10°, cos o = 0,9820°, cos = 0,94
0 = 30°, cos 0 =0,87
COS 3
Example 9;
In a 120 V, two-wire circuit the reading on the ammeter is 20 A and the wattmeter reading is 2 150 W.
Calculate the power factor.
Solution:
Real power = 2 160 W
Apparent power = V. I = 120 x 20 = 2 400 VA
The power factor is therefore 2 150/2 400 = 0,90 (90%)
When electrical installations are designed for loads thai are expressed in
watts or kilowatts, it is essential that the power factor for the load must be
known, or else the conductor size chosen may be too small for the real
curreni.
The measurement of power consumption by supply authorities consists of two
components, namely the measurement of apparent power (i. e. kVA demand)
as well as the measurement of real energy consumption (i. e. kWh). The
supply authority charges a fee on consumers whose systems function on a too
low power factor (e. g. less than 90%). In 1991, for example, the City Council
of Pretoria charged a fee of R29,27/kVA.
Power factor correction inay be considered for systems with an unsatisfactory
power facior. This can be done by making use of capacitor's (the characteristic
of a capacitor with alternating current supply is that the current I_ is leading
voltage VL and therefore "cancels out the after-current) or by means of
synchronous electrical motors (the operation of which fails outside the scope
of this discussion).
Single-phase three-wire systems
Elecirical power to individual houses and to smailer commercial buildings
are normally supplied by a 120/240 volt, single-phase, three-wire system.
The power source is a single-phase transformer with two 120 V secondary
windings (the funciioning of the transformer is discussed later). The middle
connection between the iwo windings is earihed and the conductor which is
connected to that point, is called the neutral because it functions at ground
potential.
The direction in which the currents 14 and I, ilow is such that the neutral
concil! ctor need carry only the difference between the currents I, anci [2.
When the iwo line currents are equal, the neutral current In is equal to zero.
Three-phase power generation
Because of the number of technical and economic advantages of three-phase
power, three-phase power is today being used universally to generate and
distribute large quantities of elecirical energy. The concept of three-phasepower can initiaily be easily
understood if three separate sources of emf are
visualised, each generating a sinus wave voltage that is identical in size but
which is 120° out of phase with relation to each other. If the sources are
combined in one system, each source is referred to as a phase.
In practice three-phase power is generated using one generator, by using
three windings in place of only one winding. All three the windings are
identical and are spaced equally around the rotation shaft, in other words
120° from each other. With three windings there are six points that are
connected, and the way in which they are connected determines the polarity
of each winding.
The three resultani voliage pulses will be spaced equally in time. As the
windings will cut across the N and S poles of the magnetic field at different
moments, the voltage pulses will be separated. They are separated by the
iime of 120° of rotation of the shaft: if the shaft rotates at 3 600 rpm, one
revolution will take 1/60 second. To rotate 120° therefore requires 1/180
seconds. The voltage pulse of a 60-Hz three-phase WS generator are
Therefore 1/180 seconds from each other.
The three different windings can be connected by one of two ways: either a
star-configuration (also called a wye, i. e. "Y", configuration), or a delta (the
Greek letter D) configuration.
The first advantage of the three-phase, four-wire system is that each system
has two voltage levels. The 380/220 V systern, for example, can supply
220 V to single-phase loadis, like lights and small appliances, and 380 V to
single-phase loads, iike electrical heaters, and three-phase loads, like electrical
motoi's.
A second advantage of the three-phase, four-wire system is that the neutral
conductor can be the same size as each of the line conductors. If the system
is balanced, i. e. if identical loads are connected to each of the phases, the
current through neutral is equal to zero. Even if one load is disconnected,
the neutral current (which is the vector sum of the other two phase currents)
is equal in size to the size of one phase current.
A third significant advantage of the three-phase, four-wire sysiem is that
three single-phase loads can be provided with only four conductors, instead
of the six conductors if three different two-wire systems were to be used.
This can achieve considerable savings in the cost of wiring of a building.
(c) Electrical supply to buildings
Introduction
The supply of electrical energy is one of the most important services in the
modern society - without it our society would have looked totally different.
Large electricity supply systems require significant investments in engineering
services anci buildings; it has a large impact on the appearance of the
environment and any interrupiion in power supply causes enormous
disruptions.
A complete power supply system is a collection of equipment and cables that
procluces elecirical energy and ihen distribuies it to the places where it is
useci.
A power supply system consists of ihree main operations: the generation of electricitythe transmission
of electricity over a distance
iii) the distribution of eleciricity to the consumer
The overall efficiency of a power system is about 30%.
Electricity supply in South Africa
The supply of electricity in South Africa is more than a hundred years old.
South Africa was on faci one of the first countries in the world that used
electricity on a commercial basis. Initially there were different generating
authorities, while some inines and municipalities generated their own power.
The need for a central generating authority has led in 1923 io the formation
of the Electricity Supply Commission - presently known as ESKOM. ESKOM
is not a governmenial organisation, but an independent seti-financing enterprise
that iunctions in accordance to the ESKOM Act of 1987.
in South Africa about 95% of electricity is provided by ESKOivi. In fact,
ESKOivi produces more than half of ihe electricity consumed in the whole of
Africa.
ESKOivi makes use of different methods to generate electricity, namely
hydro-elecirical plants (on small scale - Gariep dam and Vanderkloof dam),
gasturbine plants (on small scale), pump storage systems (Drakensberg
and Palmiet), a nuclear power plant (Koeberg) and, most common, steam
iurbine (coal-ciriven) plants (19 plants, including Amot, Duhva, Kendal, Komaii,
Kijel, Lethabo, iviali. nba, iviaila and Tutuka).
In contrast to countries like Canada, Norway, Sweden and Switzerland, which
predominantly make use of hydro-eleciric power, South Africa does not have
sufficient water and large rivers required to drive ihe turbines. The problem
is exacerbated by sporadic rainfall and periodic droughts. Hydro-power can
be supplied by schemes that are developed in co-operation with neighbouring
countries (e. g. Cahora Basa and Ruacana), but the reliable supply of power
is dependent upon politic-economic factors.
South Africa is, however, rich in coal. Coal is burnt and steam pressure is
built up to drive the massive turbines. Because large coal deposits occur in
the iMpumalanga, the area is known for the large power stations that are
situated there, South Africa is therefore, like countries like the UK, USA,
Russia and Germany mainly dependent upon coal-driven power stations. A
disacivantage of this type of power stations is the enormous air pollution that
is prociuced.
The large distances between metropolitan areas and the rural areas with
relatively low population densities cause unique problems for electricity supply.
ESKOM therefore operates one of the inost sophisticated distribution networks
in the world. ESKOM's power cables oí 220 000 km can circumvent the earth
five times.
Local authorities normally purchase their electrical power from ESKOM and
re-sells it to the consumer. Local authorities can however also operate their
own power stations. Pretoria, for example, provides in inore than half its
power requirements through the Rooiwal and Pretoria-West power stations.
The demand for power varies of course considerably during different times
of the day, typically exiibiting peaks around 08:00 and between 19:00 and
20:00.
Distribution networks
The use of high voltage
Power stations often are far from the areas wirere the power is required.
In the case of hydro-electric power stations, the power stations are of
necessity located at places where this iype of power generation is
possible (typically in mountainous areas), while power stations driven
by steam turbines are close to fuel sources for economic reasons (in
South Africa, typically close to coal fields).
The power that is generated, must therefore normally be carried over
long distances to the consumer. An electrical cable can provide a given
power in one of two ways: either by high voltage and a low current, or
by a low voltage and a high current (from P V !). Because part of
the electricity is lost in the form of heat losses, and this loss is direcily
proportional to the electrical current which is transported, it is preferable
that a low current (and therefore a high voltage) be used. In addition a
high curreni requires a thick conductor, which is more expensive than a
thinner conductor. Because of both ihese reasons, high voltages are
therefore used when electricity musi be carried over long distances.
Power cables and power towers
Long distance power lines are made of braided wires of copper or
aluminium. If a high mechanical strength is required, the cable contains
a steel core - especially if the conductor is made of aluminium, which
is mechanically weak. Tive cables are held in the air by towers or poles
of metal or wood and the cables are not isolated. The thickness of the
cables are determined by the size of the current which is to be carried,
and often also by the mechanical strains to which the cables may be
subjected (for example wind, the weight of the cable itself, and snow).
The conductor cable must be isolated from the poles or towers which
carry ihem; if not, the electricity will be conducted to the earth (because
the poles and towers are, of course, earthed). Isolators are made of glass
or porcelain and must have special mechanical and electrical properties
to withstand the weight of the cables, stresses as result of wind or snow,
as well as the high electrical voltages which are carried by the cables.
Typical isolators consist of several discs of glass or porcelain.
High voltage networks
The normal main distribution voltage in towns and cities is 11 000 V
between lines (voitages like 3 300 V and 6 500 V and 22 000 V also
occur, but are exceptions). Distribution from power stations is at much
higher voltages like 88 000 V, 280 000 V and 400 000 volt. The electricity
is not generated at such high voltages, however – the power ihat is
generated by AC generators driven by steam turbines is typically of the
order of magnitude 10 000 V. A transformer is therefore used to change
the voltage of the generator to the transmission line voltage.
When the electriciiy reaches the consumer the voltage must be decreased
again. For example, the normal voltage in South Africa is 380 V for
ihree-phase and 220 V for single-phase, called the 220/230 V system.
Places like Pretoria is on a 240/415 V system, while the siandard is
230/400 V systems with a frequency of 59 Hertz: The decrease from
ihe transimission voltage to consumption voltage is also done through
the use of transformers.
We therefore transform upwarcis ai the generator side and downwards
at the load side ("step-up and step-down transformers”).
BUILDING P&ACTICE - VOI. UME 1
The transformers most commonly encountered in power supply to
buildings, are those that transform a voltage of 11 kV to 220/230 V.
Transmission control
An elecirical power supply network consists of a large number of power
stations and consumers that are connected with each other. The
output of one power station is not allocated to only one area, but can
be distributed to other areas as needed. Such a network has many
advantages, but also certain disadvantages.
Transformers
The transformer is surely directly responsible for the large-scale use of
alternating current. The apparatus can change the voltage at which energy
is delivered without much loss.
When an electrical current flows through a conductor, an electrical field is
generated around the conductor. The direction of the electrical field is
determined by the right-hand rule. If the conductor carries a direct current,
the electrical field remains in position until the current is switched off. If the
conductor carries an alternating current, the excited field changes the whole
time – it rises and falls continuously and the power lines of the field move
continuously io the outside and then back to the conductor. With alternating
current a moving field therefore originates around the conductor.
if a second conductor is now placed close to the first conductor, there are
moving power lines that cui across the second conductor. Voltage is therefore
excited in the second conductor. If the second conductor forms part of a
complete circuit, a current will flow through the conductor. The direction of
the current will be opposite to that of the current in the firsi conductor.
This phenomenon forms the basis of transformer theory. A transformer
normally consists of two coils (windings) of a conducting substance, wound
around an iron core so that the two coils are close to one another. The iron
core can take many forms and provides structural support to the windings.
The main purpose of the iron core, however, is to increase the strength of
the electromagnetic field of the primary winding. The two coils are also
sometimes wound on top of one another, to ensure that they are close to
one another as possible.
There is a direct relationship between the number of windings in each coil
and the voltage of that coil. This relationship can be expressed as follows:
V/1 = N/N
where Vt primary voltageV2 secondary voltage
NA = number of windings at the primary sideN2 number of windings at the secondary side
lí the secondary coil has more windings than the primary coil, the induced
voltage will therefore be higher. If the secondary coil has less windings, the
induced voliage will be lower.
As an approximation the power that enters a transformer is equal to the power
that is produced by the transformer, i. e. the transformer has a utility of 100%
(in reality it is not true, as losses of approximately 1% to 2% are expected).
By combining this relationship between curreni and voltage with the
relationship between voltage and number of windings in a transformer, it
follows thai
!!! = N/N
where 11 = primary current12 secondary current
N = number of windings at the primary sideN₂ = number of windings at the secondary side
If 11 = 15 A, N! = 400 windings and N2 = 20 windings, it follows that
12 15(400/20) = 300 A
Example 10:
An ideal single-phase transformer has a step-cown voltage-relation of
240/5 volt. If the primary winding coniains 200 windings and the secondary
curreni is 100 A, determine:
(a) the number of windings on the secondary winding
(b) the primary winding current.
Solution:
(a) FromE2/E1 N/N
li follows that Ng = (EN)E1
(b) From12/14NA/N2
it follows that ! (12/N2)/N,
= (6 x 200)/240
(100 x 5)/200
5 windings
2,5 A
It may also be that ihere is an equal number of windings on bolh the supply
side and the output side of a transformer. In such a case the supply voltage
and the output voltage will of course be the same. All that is achieved is thai
the secondary circuit is isolated from the rest of the circuit, and such a
transformer is called an isolating transformer. An isolating transformer may
possibly be used in a building if a circuit which is not earthed is not required
for some or other reason, and it therefore needs to be isolated from the main
wiring system which must of course be earthed.
Substations
Purpose of a substation
The purpose of a substation is the following: Accommodation of the electricity supply authority's
switching gear
Safety of the building supply
Safety of the authority's transformers (if any)
Measurement of the building's electricity (meters must be placed
outside)
Accommodation of the building's transformers and switching gear
Requirements to which a substation must comply
A subsiation must comply with the following general requirements: Large enough to provide sufficient
free space for service and
maintenance personnel.
Good ventilation.
Rodent-proof, fire-proof and water-proof.
Natural light must be provided where possible. Electrical lights must
be controlled by a switch close to the door to pievent danger to
persons and make it possible that all equipment can be clearly
Gistinguished and all instrumenis, labels and notices be read easily.
No open conduciors or exposed, live parts of electrical appliances
may be within reach of windows.
Doors musi open io the outside and must be easily opened fro. m
the inside.
All cable clucts must be covered with suitable slip-free chequered
plate.
Fire extinguishing appliances must be provided.
Notices must be provided in both official languages.
Substations must be accessible to heavy equipment and
maintenance personnel.
Substation buildings must comply with the relevant requirements of
national legislation as well as with the requirements of the electricity
supply authority.
Ai a substation the voltage at which electrical energy is supplied, is
changed io a voltage that is required by the consumer. The heart of the
subsiation is the transformer. Because a transformer has no moving
parts, its reliability is very high and its lifetime is very long (typically
20 years or more).
Protective ecjuipment and switching gear are installed around the
transformer, on the high-voltage side, high-voltage equipment and on
the low-voltage side, low-voltage equipment.
The high voltage is broughi to the primary side of the transformer (i. e. the
supply side) by means of three lines. The coils of the transformer are
connected in delta on that side. The secondary side or output side is
normally connected in star because single-phase is required for most
small electrical consumption (lights and stop contacts).
This iype of transformer is called distribution transformers and standard
sizes are available, namely 530 kVa, 800 kVa, 1 000 kVa and 1 250 kVA.
The equipment is heavy. A 50 kVa-transformer weighs about 500 kg, a
i 000 kVa-transformer about 3 500 kg and a 2 000 kVa-transformer
about 4 800 kg. They are relatively big (1,5 x 2 metre) and a floor-ioceiling space of at least 2,4 metre is
required in the room which houses
the equipmeni. Transformers can be of a dry type or the oil-filled type.
Transformers are inairly damaged by overheating or sudden very large
currents (short circuits). The equipment must therefore be protected
against these faulis. It is furthermore of course necessary that they can
be switched off. Protective as well as switching equipment are therefore
required.
High voltage swiching gear
The supply authority normally provides electricity to a large consumer at
11 000 V. The distinction between a large and a small consumer varies
from authority to authority (from 50 kVa, to as much as 500 kVa in
exceptional cases).
Such a supply point forms part of the supply authority's ring disiribution
system. A ring supply unit (properiy of the supply authority) is iherefore
required. The unit consists of at least two isolators and at least one
current-breaker. At the consumer's side there will be at least one currentbreaker (ii only one
transformer and supply is present).
Normally there is at least one isolator (sometimes two or three) and as
many curreni-breakers as there are transformers in the substation.
This equipment is relatively large - 900 mm wide, 1 500 mm deep and
2 100 mm high.
Because the switching gear can be pulled out, there must be allowed as
much space in front of the switching gear as the depth of the switching
gear, while there must also be space to service the switching gear.
Connections are normally done at the backs of the switching gear and a
space of at least 600 mm must therefore be provided between the back
of the switching gear and the nearest wall.
The switching gear normally switches off the transformer ur der
overcurrent conditions, in other words wien more current flows than
the transformer has been designed for.
The transformer is normaliy also switched off automaticaliy wher:
(a) gas generation occurs in the oil of the transformer in the case of anoil-cooled transformer (the
Bucholiz relays is used for this purpose).
(b) the transformer becomes too warm.
When the transformer is switched off for any of the reasons (a) or (b), a
siren or horn is set in operation as maintenance personnel must first
check the transformer before it is switched on again.
This equipinent therefore does not protect the transformer against shortcircuit currents. This is done on
the low voltage side.
Low voliage switching gear
The low voltage side of the iransformer is connected to a circuit-breaker.
This circuit-breaker protects the transformer only against overcurrents.
The circuit-breaker acts mainly as a switch. From this circuit-breaker
the power is brought to distribution rods – the so-called busbars. From
these busbars the power is distributed to the distribution boards. The
conductors are fixed to the busbars by means of bolis.
Between the sub-supply and the busbar an isolating switch is norinally
installed with high break capacity-fuses. These isolators have the ability
to react quickly to a short-circuit current - much quicker than a circuitbreaker. The disadvantage of a
fuse is however that it must be replaced
afier it has blown. It is therefore used for abnormal conditions like a
short-circuit and not for overcurrent protection. In some cases one inay
even encounter an isolating switch as well as a current-breaker for a
sub-supply circuit.
SUILDING SERVICES
Low-voltage distribution boards are approximately 1 200 mm deep and
2 100 mm high, while the length is dependent upon the number of
transformers and sub-supply circuits. Remarks about space in front of
and behind hign-voltage switching gear are also applicable here.
The properties of transformers do not correspond a huncired per ceni,
and the parallel-operation of transformers is therefore avoided (i. e. when
the low-voltage side of two of inore iransformers are connected to one
another).
For each transformer there exists therefore a set of busbars that is not
connecied with the busbars of oüher transformers. It may, however,
happen that a transformer irips ouit, resulting in the sub-supply circuits
on the transformer being without power and a part of a building complex
being in the dark. In such a case the busbars of such a transformer
can be connected to the busbars of a another transformer by means of
a busbar coupling. The busbar coupling can be an isolator or a circuitbreaker switch, in which the HRCfuses are replaced with the correct
size copper busses. There will aiways be one less busbar coupling than
there are transformers, i. e. for 2 transformers there is 1 busbar coupling,
for 5 transformers there are 4 busbar couplings, etc.
The circuit-breaker from each transformer and the busbar coupling is
normally interlocked in such a way that only two pieces of equipment
can be on at the saine time. Both circuit-breakers can therefore be on,
but then (a) the busbar coupling is off, or (b) one circuit-breaker and the
busbar coupling is on and the second circuit-breaker is off. It prevents
parallel operation of the transformers.
Connection between equipment
Connections between the high-voltage swiiching gear and the transformers
normally occurs by means of high-voltage cables, whether of the papercovered or PVC-types.
The cables can run overhead on cable trays from one point to the other,
but it is more common that the cables are laid in cable ducts in the floor.
Such cucts are normally 600 mm or more wide and 600 min or more
deep. A logical route is normally followed. Ducts must be watertight,
cables must be fixed neatly and before cables cross each other bridges
must be provided. Cables are often fixed against the side of the duct by
means of some shelf or clamp system.
Ducts are covered by means of metal plates oſ sufficient strengin ihat
equipment can be moved.
One cabie of the correct size is suíficient for the high-voltage side.
On the low-voltage side the current is very high and a cable bigger than
185 mm2 is too unwieldy. A number of cables of 185 mm2 diameter
(4-core PVC SDP PVC) is therefore required. For a 1 000 kva
transformer it is approximately 5 cables. Once again use is made of
cable ducts to house the cables that connect the transformer with its
low-voltage switching gear, although use is also sometimes made of
enclosed busbars as for the rising busbars (it is normally done overhead).
(d) Power supply to the building
Introduction
Electricity to the building is norinally supplied by ESKOivi, either directly or
via a municipality. The centre is billed monthly for this service and the
consumption. For a connection up to 56 kVA the supply will be 380 volt
3 phase. As relatively few developments have such a low load most will fall
in the next category.
When the requirements are over 56 KVA, an HT (high tension) supply is
required. This supply is usually at either 6 or 11 kV (6 000 or 11 000 volts)
which means the centre has to have its own transformer. If the transformer
is purchased by the developer, a reduction in the tariff will apply. Alternatively
the transformer remains the property of the municipality. The size of the
reduction in tariff depends on the municipal area.
It is extremely important that ihe manager knows where the electrical supply
comes from and who he must call in case of supply failure. For this he needs
to have a very good relationship with the Council or the authority that supplies
the power. Power shut-downs can cause havoc and the earlier the tenants
are inforined about the expected duration of these, the better.
Power from the power station is taken to the substation, by making use of
overhead cables or by laying the cables underground. The power supply to
the subsiation is at say 11 500 V, and is stepped down io 380 V by means
of a step-down transformer.
Al bigger buildings the cables go from the transformer room to ie inain
distribution board.
There is normally one main distribution board per floor of a multi-siorey
building. From the main distribution board the conductors branch to a number
of sub-distribution boards.
In the case of shops or offices the supply authority does not measure the
electricity for each individual shop or office. Only one meter point occu!'s
and an account for ihe iotal consumption is seni to the owner or ienant of
the total building.
The owner on his part recoups this cost from the different tenants by:
(a) making an estimate of the electricity consumption and converting it io aper area unit cost (cent/m2).
This cost is then included in the rental.
The tenant therefore pays indirectly for his electricity. This is done
especially in offices.
(b) installing a separate meter on the floorboard for each tenant. This meteris provided and read by the
landlord. Most often use is inade of outside
firms io take the readings and send the accounis to the tenants. Thismeihod is ofien used in sectional
title complexes.
Each such floor distribution board will therefore have a meier for each ienant
(usually three-phase in bigger buildings). There will also be a lock - which
is under control of the landlord – and an isolator for each tenant's supply. In
addition there will be a circuit-breaker that protects the sub-supply circuit to
the tenant.
On the tenant's premise there will be a distribution board from where power
is distributed to each light, socket-outlet and other equipment.
It is important that the manager becomes familiar, in broad terms, with the
electrical distribution system in the building. This means that he must know
the position of the various distribution boardis and what areas are fed by the
individual boards. The reason for this is that he must be able to assist in
emergencies, such as fires, floods, etc. For the same reason it is imperative
that the manager keeps a set of plans showing the boards and the areas
they feed. This plan must be kept up to date. Cross feeds from one area to
another should be prevented at all cost to avoid the possibility of live wires in
an area if the supply has been switched off. This means that the contractors
working on the electrical sysiem in the centre must be very strictly controlled
and a system of work permits for coniraciors introduced to monitor ihose
changes.
Emergency power supply
It is often necessary that provision is made for power supply when the supply
authority's power supply is inierrupied. Examples of such neecis are lifts in
a tower block, staircases and working booths, theatres for performances,
elecironic computers, defence equipment, operation theatres, life-support
systems, poultry breeding batieries, chemical plants and prisons. in addition,
all facio: y premises (whether offices of workshops) that are used during certain
hours must be provided with emergency lighting. In such cases emergency
power is provided by a mechanical (normally diesel) driven generator and/or
batteries.
The diesel generator is normally used when a lot of electricity is required,
when alternating current is required and when a short interruption is not
important. The generator(s) can be big enough to supply the total power
needs of the building. If it is connected to the main supply directly to the
supply authority's meters, it provides standby facilities for the whole building.
The outlet of a diesel generator may never be connected to the supply
authority's supply. When the same equipment must operate on normal power
as well as emergency power, special precaution must be taken to prevent
that both are not on simultaneously.
Diesel generators are large. A 400 kVA generator is about 3 metres long and
1,2 metres wide, and a metre space is required around the equipment. In
addition, it is necessary that the generator must be cooled and that sufficient
fuel (normally enough for at least 12 hours' operation) be stored. The quantity
of fuel can vary and may need to be sufficient for 48 hours in certain conditions,
like remote areas.
Diesel generators are very noisy and it is often desirable that soundproofing
be provided. Any casing should, however, have openings for fresh air to the
engine and for gas emissions. Of course the openings limit the measure of
soundproofing that can be obtained.
It is cheaper and normally sufficient to provide a smaller generator that
provides only the more important outlets with power. In this case the
distribution must be arranged so that outlets at one point can be switched
over from main power to emergency power, and there inust not be a connection
of the emergency power with outlets not requiring emergency power. In
smaller buildings it is often possible to provide a separate wiring system from
the emergency generator, with different outlets. The disadvantage of this is
ihat equipment must be disconnected from the main outlets and be connected
at the emergency outlets when a power interruption occurs.
An emergency generator can be started by handi or automatically. Switching
on by hand is simple, but involves a delay ihat may be unacceptably long.
This delay can be avoided by installing a sensor which will detect a voltage
drop in the main supply and automatically switch on the emergency generator.
It takes from 8 to 10 seconds for a diesel generator to coine to top speed.
Even this clelay may be too long in certain applications. A way in which to
avoid this delay, is to connect the generator with a cluich to a flywheel. When
a power interruption occurs, the generator is switcheci on. The alternator is
kept going through the flywheel unül ihe generator is at speed and is connecied
through the clutch with the alternator. This method is obviously expensive
and is only used for relatively sinaller power outputs for special conditions,
like telecommunication and power for aircraft landing systems.
Apart from the supply of emergency power, generators can also be used to
provide peak-loads, io save the cost that the supply authority may charge
for peak loads. In this case the generator will be switched on automatically
with a kVA meter instead of a voltage detector, but otherwise the operation
is the same.
Batteries are normally used when ihe amount of electricity required is low or
when no interruption can be iolerated, for example for emerger. cy lighting or
for uninterrupied supply to computer equipment. The battery is charged
continuously from the main supply during normal conditions.
The batteries provide power until the inain supply is repaired or until the
emergency generator is operating.
Lead acid batteries are often used for uninterrupted power supply, but nickel/
alkali batteries have a longer lifetime and do not cause corrosion problems
like lead acid batteries. The delivery and storage of acid and distilled water
must be kept in mind when the installation is designed.
Because computers are sensitive to voltageand frequency-fluctuations the
computer equipment is often fed into a network that smoothes supply
fluctuations and suppresses surges thai are caused by other equipment
connected to the same supply.
Although it is possible to install a unit big enough to feed the complete noninterruptable load, smaller,
cecentralised units are preferred for economical
reasons and to provide a degree of standby for fauli conditions.
Again, the manager has to know what services are connected to the
emergency system and a very strict control must be exercised to avoid extra
loads being connected to the system. To control this the work permit system
can be utilised. A special note on the work permit regarding the conneciing
of loads to the emergency system is noi out of place.
In order io make sure that the emergency sysiem will operate when required
it must be tested regularly. The recommended frequency of testing is once a
month for starting and running smoothly and at least twice a year for capacity.
The laiter is usually cone by simulating a total power failure for the entire
building. During this lest all services connected to the sysiein must be visually
checked.
The tenants must, of course, be notified when such a iest is to take place.
Another very important test is to co a check-back after an actual emergency,
in order to verify that the connected loads operated.
The following items should be connected to standby power:
The entire common area lighting system
The entire common area power system
The security and public address systems
Ali external lighting
Lighting to all escape passages and public toilets
Smoke ventilation system
Sprinkler pumps
Any essential services in industrial buildings
Distribution systems in buildings
The mutual connection between distribution boards and distribution boards
and distribution boards and other distribution boards determine the type of
distribution system that may occur in buildings.
There are three types of distribution systems for buildings or building
complexes: the radial system, the loop system - either without busbars
(“ring-main") or with vertica! busbars ("rising main”) – and the ring system.
Combinations can also be used.
Radial system
With a radial distribution system all services to subsidiary distribution
panels of distribution boards connect directly with the main distribucion
board. The installation and operation of the radial system is simple, bui
it cioes not offer an alternative power supply when the main power is
interrupted. See figure 5.19.
Distributionboard
Subsupply
Subsupply
Distribution board
From supply authority's
isolator and meters
Distributionboard
Figure 5.19 Radial distribution system
Distributionboard
Loop system
In this system each distribution board is not connected with the supply
poini, but with a previous distribution board. The main distribution board,
for example, is connected with three sub-distribution boards in a radial
system. From each of the sub-distribution boards there are eight floor
distribution boards. In stead of now taking a sub-supply to each floor
distribution board from the sub-distribution board, a sub-supply is only
taken to the nearesi distribution board. This distribution board feeds the
following distribution board, etc. up to the last (8th) distribution board.
See figure 5.20.
This system saves on conductor sizes, but if there is a fauli on one subsupply circuit, not only the
disiribution board servicing the sub-supply is
without power, but also all the subsequent distribution boards.
The system is used especially where a number of buildings are spread
over a site, as for example a school, where the loss of supply is not
critical.
It is also often used in large towerblocks, but then a special conductor
arrangement, namely rising busbars, is utilised. Copper rods are used
as conductors. The rods are isolated from each other and protecied in
a inetal casing with ihe result that faults are unlikely once ihe system
has been put in operation. The rising busbars are instailed in a rising
duci in the building. Only the busbars and other electrical equipment
may be insialled in the rising duct.
These rising busbars are relatively expensive and can normally only be
considered if the building is higher than 8 floors. In very high buildings
there may be more than one set of rising busbars, depending on the load
of the building. The first 8 floors, for example, may be serviced by one
sei of : 200 A rising busbars, the following 8 floors by a second set, etc.
The system becomes especially economical where the loads of the
different floors are approximately equal, like in tower blocks for offices.
viost buildings will be a mixture of the radial system and the loop system.
Determination of conductor size, size of protective equipment, etc. is
similar to that of other systems. It should only be remembered that the
load on each distribution board is equal to the load of the distribution
board before plus the load of the equipment that is serviced by the
distribution board itself.
In the case of a towerblock with typical (repeating) floors the load of one
floor is calculated and then multiplied with the number of floors serviced
by one set of busbars.
The rising busbars are normally suitable for low voltage (less than 600 V)
and consist of a bar (or bars) for each line and one (or a composite) for
the neutral. The earth conductor need not be larger than 70 mm2 and
is normally taken up as a string conductor.
H
Distribution board
Distribution board
Distribution board
Subsupply
From isolator
of supplier
Distribution board
Figure 5.20 Loop distribution system
Ring system
This system is mainly used in a high-voltage system (1 000 V or more)
and/or where the interruption of the electrical supply may cause serious
problems.
In this system at least two supply cables are brought to the premise of a
buildirg. These suppiy cables come from different supply points or can
be connected to at least 2 different supply points in the supply authority's
net. If one supply falls away, the supply can be repaired quickly through
supplying power for the second supply by opening or closing the right
switches. The faulty supply is then isolated from the supply net.
The system normally works as a loop system, i. e. power flows of one
board to a second board and from there to a third, but instead of it
being ended, the last board is connected again with another supply.
Somewhere in the middle a switch is opened and the 'ring' is ready.
At each distribution board one cable enters and one cable goes out.
Isolators are used here. In addition a load is tapped by means of a
circuit-breaker. Such an arrangement of two isolators and one (of more)
circuit-breakers, is called a ring-supply unii.
In large buildings of building complexes more than one sub-station may
occur. They are then normally connected mutually on a ring-system at
ihe high-voltage sides.
Sizes of cable and protective equipment are calculated as before. There
is not a wide choice, however, and standard equipment is utilised.
The short-circuit current word is also limited by other equipment to
approximately 31 kA or less, which is suitable for all equipment. Note
that this only applies for voltages up to 11 kV. Above that, short-circuit
currents are bigger. It does not affect us here, however.
Circuits in buildings
Single-phase circuits
The wiring for a group of socket-ouilets in a house is iypically on a loop
system (the circuit consists of iwo current-carrying conductors and an
earthwire that is connecied from one socket-outlet to another.
Lighting circuits
Circuits for lighting having their origin at the distribution board, is in
general limiied to a total load of 1 000 W and require 5A fuses and switches.
In larger buildings 15 A fuses and switches are used, because of ihe
larger total load on the circuit. Wiring to light points is done according
to the loop ("loop-ini") method.
5.2.2 Lighting and environmental control
Introduction
Lighting is required for the obvious reason of allowing people to see where
they are going and give safe access to areas where there is no natural light,
either because of no natural light being able to penetrate or because of it
being dark outside. Besides this, lighting plays an important role in enhancing
ihe decor inside, as well as outside the centre. The cost of lighting is high,
firstly because of the electrical power it draws and secondly because of the
effect, on the air conditioning system, of the heat produced by the lights.
Usually ihe amount of power required to remove the heat from the lights is
approximately 30% of the electrical supply to the lights. In other words, if
ihe lights absorb 100 kVA, the additional power required to remove the heat
is approximately 30 kVA. For these reasons the manager must be aware,
at all times, of the lighting systems installed in the centre. Lighting levels do
not need to be equally high in all areas. For instance, in service routes and
areas not accessible to the public, lighting levels do not have to be as high
and fluorescent lights, known for their efficiency and long life, can be used.
The manager has to have a basic knowledge of the different types of
lighting systems available in order to evaluate them and to be able to
support proposals for energy savings. He must also be aware of the
servicing procedures for the lights as dust can have a significant effect on
the lighi output of the different fittings. Some knowledge regarding how
long the different types of lamps and the accessories last is also essential to
evaluate the servicing procedures. For example, very few people know ihat
a fluorescent light should lasi at least 7 500 hours, which is equivalent to
1,5 years service at 10 hours per day, or nearly a year, if the lights burn 24
hours a day.
Lighting design
The three main purposes of good lighting are the following (SABS 0114:13): To further the work or other
activities carried on within the buildings;
To contribute towards the safety and health of people using the buildings;
To creaie, in conjunction with ihe siruciure and decoration of the buildings,
a pleasing environment thai stimulates interest and is conducive to a
sense of well-being
iviany factors must be considered in the design of a lighting system. The most
important factors that should be taken in to consideration can be summarised
as follows (the relative priorities depend on the specific situation – cf. also
SABS 0114:13): Quantity of light, is determined by the nature of the work and the lighi
output of the light and light luminaires. It is normally specified by
illumination level in lux.
Natural light - Can be used as the only light source or to supplement
artificial light sources.
Colour quality - Is determined by the raiure of the work and the
colour-creating properties of the light source. It can be specified by
spectral distribution, colour temperature and colour l'endering index.
Glare - Is determined by the brightness and contrast of light sources and
surfaces, and the angles of sight. It is normally specified by a glare index.
Flickor - A property of certain types of lamps. Can cause stroboscopic
effects.
Directional quality – Is deiermined by the three-dimensional effect that
is required and the naiure of the light and the light luminaires. It can be
specified by vector and scalar illumination.
Energy consumption - Is determined by the light outputs of lamps
and the use of switches. All lamps produce heat which can be a
significant source of heat take-up in a building. Windows that can let in
natural light can be a significani source of heat loss or gain.
Cost - Is Geiermined by the initial cost of the light fittings, the replacement
cost of the lamps and the electricity consumption of the lamps.
Physical properties – include size, appearance and durability of fittings.
Emergency lighting - If required.
Choice of lamp types
The choice of a lamp-type for a specific application is a combination of
practical, aesthetic and economic factors. Table 5.1 provides a summary of
ine advantages and disadvantages of the most important light sources
discussed in this inodule, as well as typical applications.
Table 5.2 provides an overview of certain characteristics of the most important
types of light sources. Obviously une caia is approximate because lamp types
vary so much. In addition the data will change with time as new developmenis
occur. In spite of these difficulties, an effort was made to provide an
overview of the most important characteristics in the table.
Table 5.1 Advantages and disadvantages of light sources andtypical applications (adapted from Hughes,
1988:139-141)
incandescent lanips
AdvantagesPoint light source, light distribution pattern is easy to control
Low initial cost
Simple, no ballasts required, no ballast noise
Light output not influenced by environmental temperature
Small, compact armatures
Very simple to dim
Pleasant colour rendering for the human
No delay with starting or re-startingNo stroboscopic problems on 50 hertz
Disadvantages
* Very low light rendering (except LS lamps)
* Very high operational temperature
@ High infrared component
* Very much influenced by voltage fluctuations
® Exceedingly bright sourceShort life (tungsten-halogen lamps have longer life)
Limited to lower voltages
©
Applications
As a result of their low light rendering and short life, incandescent lamps
normally not a good choice for large area commercial, industrial and
exterior lighting. Incandescent lain. ps is a good choice for social areas
where good colour rendering and a waim, pleasant effect are required,
for accent and exhibition lighting where good lighi control is necessary,
and for decorative lighting.
Icontinued...
Standard fluorescent tubes
AdvantagesGood lighi rendering
Very long life
Low brightness
Low operational temperature
Low infrared output
Good colour rendering
Can work ai inigher voltages
Only smali delay with starting and re-starting
Disadvantages
@ Not a point light source, light distribution more difficult to contro!
* Requires ballast; extra weight; noise
© Higher initial cosi
* Very much influenced by environmental temperature
® Large; requires unwieldy arinatures (excepi SL and 2D types)
® Recuires special ballasts for dimming
Applications
Fluorescent lights are commonly used for the illumination of large
areas of general illumination in offices and industrial plants. It is the
source of probably 70% of all lighting in S. A.
High-intensity discharge lamps (mercury, metal halde and high
pressure sodium lamps)
Advantages
© Very good light renderingVery long life
High output in compact size
Essentially a point light source
Negligible infrared component
Light output not influenced by environmental temperature
Can work at high voltages
/continued...
DisadvantagesCan give colour rendering problems
High initial cost
Requires ballast; extra weight; noise
Very bright light source
Very difficult and expensive to dimLong heating and re-starting times
© Stroboscopic effect may be a problemStarting problem in cold weather
Applications
Commonly used for high interior industrial applications and for many
exterior applications, such as street, parking area and security lighting.
Being used increasingly for interior commercial applications, as better
colour-rendering meta! halide lamps are being developed.
Table 5.2 Characteristics of light sources
Lamp iype
Incandescent lamp (GLS)
Tungsten halogen (TH)
LS tungsten halogen
Fluorescent tube (MCF)
ivercury vapour lamp (IBF)
iMetal halide lamp (MBI)
Low pressure sodium lamp
(SOX/SLI)
High pressure sodium lamp
(SON)
Power
(wait)
40-200
500
50
20-125
125
250-3 500
35-180
70-1 000
Lightflood
(i. umer)
800
11 000
11 000
3 000
22 500
40 000
33 000
50 000
i. ightrendering(lm/W)
14
22
22
50
50
80
50
125
Approx. Approx. life price:
(irours) lamp only
1 000
2 000
3 000
10 000
20 000
15 000
18 000
24 000
R4
R30
R60
R8
R20
R90
R50
R70
5.2.3 Alarm and security systems
(Acknowledgement: This section is based upon material prepared by
C van der Walt.)
(a) Principles
Security for commercial developments
Why security systems?
The motives why individuals, groups and/or organisations would try to
intrucie into a building or complex can include the following:
>>
Political inotives
Publicity for the specific group and/or organisation
Disruption of society by damage and destruction of strategic
installations
Industrial and financial motives
Process know-how – that is, industrial espionage
Theft of raw inaterials
Theft of completed products
Theft of equipment
Theft of money and valuable items and wares
Disruption of opposition and activities of competitors
Personal motives
Personal grudges – for example employee wiro has been fired
ivialicious damage by vandals
Strong personal convictions – for example opponents of
vivisection
Other irrational reasons
Requirements for a security system
The requirements which a security system should saiisfy are as follows: The system must be flexible to
accommodate future changes cheaply
and easily
The system musi exhibit a low level of false alarms
The system inust exhibii a positive alarm or detection level
The sysiem must be cost-effective with low cyclical and operational
costs
The sysiem must be simple to operate
Factors to be considered when establishing a security system
The factors that must be considered when establishing a security
system are as follows:
Type and nature of activities that occur in the development
Risk and threai that result from political motives
Risk and threat that result from industrial and financial molives
Risk and threat that result from personal motives
The client's specific requirements
The clieni's organisational structure – with specific reference to the
client's security department
Available iechnology
Costs for the supply, installation and operation (with special emphasis
on cyclical costs) of the security system - it is absolutely essential
that the costs for the security system should not seriously influence
the viability of the development
Flexibility of the system to accommodate future cianges cheaply
and easily
Integration of the securiiy systems with other building-monitoring
services, building function and administrative functions
The degree of sophistication and training of the client's security
personnel
Effect of the security system on the client's day-to-day activities
The electronic security system
Main components of a security system
The main components of an elecironic security system are as follows: Control apparatus
Sensors and peripheral equipmeni
Communication link, via wiring and/or telemetric medium, between
the control apparatus and sensors and peripheral equipment
Building design
liems for consideration during the design process
The following items should be considered in conjunction with the client
and security consultants during the design process: The client's specific requiremenis
Risk with relation to the aim and application of the building(s)
General site layout
Position of property bounciaries
Position of parking areas
Positions of fences
Number and position of entrance and exits
Number and position of emergency exits
Position and location of high risk buildings
Detail about construction materials
Details about doors, windows and locks
Details about overhangs, balconies anci niches
Details about service ducts and channels for accommodation of
security services
Accom/nociation for securiiy personnel and equipment
Uninterrupted and emergency power supply
The effect of lighting, thunder storms and static electricity
Available funds vs. technology, as well as threats (risks) that may
possibly change
(b) Control systems
Introduction to typical securlty systems
Components of a typical security system
The following items and facilities can be part of a iypical security system:
Central computer control unit
Personnel and visitors access conirol system
Vehicle access control sysiem
Fencing or perimeter control system
Site supervision and control
Protection against intrusion in buildings and sensitive areas
iionitor and control of other building services
Access control systems
::
Purpose of access control systems
The purpose of access control systems is ihe control of: personnel thai enter and leave the building and
internal sensitive
areas in the building
visitors thai enter and leave the building and internal sensitive
areas in the building
vehicles that enter and leave the site
reception and dispatch of goods
BUILLING PRACTICE - VOLUME 1
Access control cards
The cont: ol of personnel, visitors and vehicles can be done by means of:
normal plastic type identification cards
inductive-magnetic cards
Wiegand cards
holography – the comparison of fingerprints, voice, signature or
profilespecial magnetism - infra-red-barcode cards ("barcode")
Note that technological changes are making other, new types of control
systems possible.
Characteristics of the diffsrent types of access control cards
Table 5.3 Access control cards
CHARACTERISTICS
TECHNOLOGY Card reader Visibility of codingForgery
rejection rate By the eyes By X-rays
Inductive-magnetic
Wiegand
Holography
Special magnetism
No
No
No
No
Sometimes
No
No
Sometimes
Difficult
Very difficult
Servicelife
Very difficult Reasonable
Difficult
Table 5.4 Resistance to normal wear of access controlmechanisms
TECHNOLOGY
Inductive-magnetic
Wiegand
Holography
Carci
weaiitering
Special magnetism Average
RESISTANCE TO NORMAL WEAR
Scratch o!
sur! ace
on card
Wagnodicfield
exposure
Lost
information
Very good Very good Very good Very good
Sometimes
Reasonable
‫܀‬
Physical access control mechenisms
Access control mechanisms can include one or more of the following
iacets:
Control of personnel and visitors by means of: Revolving gates: full-, halfand hip-height
Doors: pneumatic-, hydraulicor electric-drivenSluices: pneumatic-, hydraulicor eleciric-driven
Control of vehicles by means of: Booms: pneumatic-, hydraulic-, electricor hand-driven
Revolving or sliding gates: pneumatic-, hydraulic-, electricor
hand-criven
Characteristics of the different types of access control mechanisms
Table 5.5 Characteristics of access control mechanisms
TECHNOLOGY
Revolving gates
Doors
Sluices
Booms
Revoiving or sliding gate
Fencing systems
CHARACTERISTICS
Voluns/hour Maintenance
Types of fencing systems
High
Reasonable
High
High
Cost
Reasonable Reasonable
Fencing systems can be one or more of the following iypes: Single fence
Double ferice
Material of fencing systems
Fencing sysiems can be made up of one or more of the following
materiais:
Wire and metal in different configurations
Concrete and brick in different configurations
Characteristics of the different types of fencing systems and
materials for foncing sysisms
Table 5.6 Characteristics of fencing systems
TYPE AND
MATERIAL
OF FENCE
Single fence
Double fence
Wire and metal
Concrete and bricks
CHARACTERISTICS
Aesthetics Maintenance Cost Security provisiti
Reasonable Reasonable
Poor
Reasonable
Sensors for exterior use
Reasonable
Very good
Reasonable
Types sensors for exterior use
Sensors for exterior can be made up of one or more of the following
types:
viicrowave type
Active infra-red type
Elecirical field type
Microphonic cable type
Lever switch type
Vibration type
Wire-under-tensile stress type
Magnetic type
Seismic type
Pressure difference type
Closed-circuit television cameras
Characteristics of the different types of sensors for exterior use
Table 5.7 Characteristics of sensors
WHERE
INSTALLED
Not fixedon
fence
Fixedon
fence
Underground
Microwave
Active infra-red
Electric field
Electric field
iviicrophonic
Lever switch
Vibration
Wire-undertensile stress
iMagnetic
Seismic
Pressure
difference
Intruder
inovoinerst
x
CAN DETECT
Nor-magneticobjecis
Under
tunnelliang
x
XX
CAUSES OF FALSE ALARMS
WHERE
FXEC
of sensors for exterior use
Table 5.8 Causes of false alarmns for the different types
POSSIBLE
CIRCUMVENTION
TYPE
Lightning Tremors
Poor
TransientBig Small
pienomana interierence animals animals
Birds Fog, snowand rein
installation
METHODS
Microwave
Undertunnelling
Undertunnelling, ladders
Undertunnelling
Undertunnelling
Undertunnelling, ladders
Not fixedОП
fence
Active infra-red
Electric field
Electric field
Microphonic
Lever switch
Fixedon
fence
Ladders
Vibration
Undertunnelling, ladders
Wire-undertensile stress
Undertunnelling, ladders
Non-magnetic metals
Bridge, mattress
Magnetic
Seismic
Underground
Pressure
difference
Bridge, mattress
TYPE
TV
25 mm 16 min Interior Exterior
tube tubeuseUSE
Hiiurnination requiredCost
High Average Low Dark High Average Low
The use of television as a communication system
Table 5.9 Types of television for interior and exterior use
Vidicon
Newvicon
x
Silcon-Vidicon
SIT
ISIT
x
CCD
Sensors for interior use
Types of sensors for interior use
Sensors for interior use can be one or more of the following types: Vibration/seismic type - applied in
and at saíes, windows, doors
Ultrasonic type - applied in anci at passages, windows, doors
Microwave type - applied in larger areas like stores and
warehouses where windows do not generally occur
Active infra-red type - application in larger areas like stores and
warehouses
Passive infra-red type - applied in and at smaller areas like offices,
windows, doors
Electro-magnetic iype - applied in metal detectors
Can ciclect
Movement Damage Dr!!! rietach to doors ami
Intruder or window lack
Causes of false alarms
Sma: i LightningPoor
animalsInterference Installation
Table 5.10 Characteristics of the different types of interior
PRINCIPLE
Functioning
infiuenceciby:
Tre nors
TYPE
OPERATION
Vibration/ Piezo-electric
seismic
Power
interruption
SIosuas
Ultrasonic
Power
interruption
Microwave
Power
interruption
Space
Active IR
Power
interruption
Passive IR
Slow
movement
Proximity
Electromagnetic
Do not
wear metal
Fire detectors
>>
Types of fire detectors
One or more of the following iypes of fire deteciors can be used in a
development: lonisation detector - applied in:
hotel rooms
offices
Optical detector - applied in:
operation theaires
Heat detector - applied in:
chemical plants
fuel storage depois
Infra-red detector - applied in:
chemical plants
Linear detector - applied in:
large areas like stores
inuseums
Table 5.11 Characteristics of the different types of firedetector's
TYPE
Ionisation
Optical
Heat
Infra-red
Linear
Sinoke
Smoke
COMPARES
Rate of rise in temperature
Flame
Smoke
AVAILABLE IN
ADORESSABLEMODUS
Yes
Yes
Yes
No
No
SUILDING SERVICES
(C) Equipment control
One or more of the following types of services can be conirolled and monitored
froin the central computer control panel:
Air-conditioning
Electrical supply
Emergency supply
UPS
Civil engineering services
Lighting
"White" sound
Communication
Security
LiftsFire deteciion and extinguishing
Table 5.12 Services control from the central computer panel
PLANT
Air-conditioning
CCHTROL
Fans on/off
Power on/off
Valve open/closed
Electrical supply Circuit breakeron/off
Stand-by supply
UPS
Circuit breaker
on/off
Load on/off
Civil engineering Pumps on/off
servicesValves open/close
Lighting
Zone lights on/off
Dimming
MEASURING
PARAMETERS
Temperature
Water level
Air flow
Supply voltage
Supply current
Frequency
Power
Supply voltage
Supply current
Frequency
Fuel level
Output voltage,
current, frequency
Water tank level
Flow
ALAFIS
Power fails
INDICATIONS
In working order
Circuit breaker Circuit breaker on/off
trippedTransformer tap
Transformer alarms position
Battery voltage low Circuit breaker onmanual
Trip on fault
Trip on fault
Pump tripped
Supply failure
Engine running
Main supply on/off
UPS on by-pass
circuit
Pump runs
Pump on manual
Power available
Lights on/off
/continued...
PLANTT
Masking sound
Communication
Intercom
PAX/PABX
Radio
Security
Closed-circuit
TV
Perimeter
protection
Indoor sensors
Lifts
Fire detection
and
extinguishing
COATiO.
System on/off
Volume
Circuit select
Tone or DC remote
desk selective
calling
Pan, zoom, tilt
camera select
Enable/disable zone
Enable/disable zone
Lift call
Lift scheduling
Check circuits
Zone selection
Trigger audible
devices
Fire dampers close
MEASURING
PARAMETERS
TX power
Lift speed
Lift load
Fire pump flow
ALARINS
Supply failure
Supply failure
Power module
failure
Charger failure
Battery supply
failure
Power module
failure
Supply failure
Intrusion alarm
Zone alarm
Door alarm
Tamper alarm
Supply interruption
Panic alarm
Fire alarm
Power failure
INDICAIRCUS
System on/off
System available
System available
Power on
Camera selected
Power available
Power on/of
Alarm zone on/off
Power on/off
Zone on/off
Lift in motion
Lift position
Detector/zone
position
Zone evacuated
Gas released
APPENDIX
SI-UNITS
Sl-units (Système International d'Unités) were accepied internationally in 1960.
There are seven basic Sl-units:
Basic quantity
length (L)
mass (iv)
iime (T)
elecirical current
iemperature
light intensity
amouni of substance
metre
kilogram
second
amperekelvin
kandela
mole
Symbol
m
kg
S
A
к
cd
mol
All other units (e. g. dersity, pressure, elecirical charge, eic.) are derived from one
or more of these basic units.
The symbols for Sl-units are the same for singular and íor plural (10 m, 3 kg, 100
A, etc.). There is no fullstop after the symbol (except of course at the end of a
sentence). A composite symbol can be written in index form (e. g. ms-2) or with a
solidus () which indicates division (e. g. m/s2) and a fullstop (.) which indicates
multiplication (e. g. N. m).
The dimensions of a quantity indicate how the quantity is related to the basic
units. The dimensions of speed, for example, are (LT-'], and that of acceleration
is [LT-2). When calculations are done, care should be taken that the two sides of
an equation are dimensionally identical, for example:
density (ivi. L-3) = mass (M)/volume (23)
In a correct equation, the units on both sides of the equation are iherefore also
identical, for example:
density (kg. m-3) = mass (kg)/volume (m3)
Exponents are used to indicate multiples or sub-multiples, for example 5 000 000
is indicated as 5 x 106, 1/i 000 is indicated as 10-3, etc. Exponents are added with
multiplication and subiracted with division, for exampie:
106 x 103 = 106+3 = 109
and 1013 : 107 = 1013-7 106
NB
(D)
Prefixes are used io indicate multiples and sub-multiples:
Quantity
10-12
10-9
10-6
10-3
10-2
10-1
101
102
103
106
109
1012
Note:
Prefix
pico
nano
micro
milli
centi
deci
deka
hekio
kilo
mega
giga
tera
Symboi
m
P
с
d
dia
k
vi
G
You should be fainiliar with the use of the metric prefixes milli-, micro-, kilo-,
mega-, etc. as well as their abbreviations.
5.3 AIR-CONDITIONING
5.3.1 Definition of heating, ventilation and air-conditioning
Heating, ventilation and air-conditioning (HVAC) can be defined as the
simultaneous control of room temperature, humidity, air cleanliness and air motion
(Shuttleworti), 1983). The term "air-conditioning" ("AG") is more commonly
used to describe one or more of the functions of an HVAC system, such as the
cooling, heating dehumidification, humidification, filtration and circulation of air in
a room or building.
5.3.2 The need for air-conditioning
Air-conditioning is required for the following purposes: To cool the air in a room or building under high
heat loads.
Example: High outside temperatures in summer.
To heat ihe air in a room or building under high cooling loads.
Example: Low outside temperatures in winter.
To dehumidity room air under high lateni loads,
Example: Excessive perspiration in a gymnasium.
To humidity room air in cases of excessive dehumidification.
Example: High paper mass in a building absorbs moisture, e. g. in a fibrary.
To circulata air in the room.
Example: Prevention of "dead spots" and draughts in a room.
To filter incoming and circulating air. Examples: High dust loads, pollution, sick building syndrome.
Improper operation of an air-conditioning system has the following undesirable
effects on occupants and building equipment: On occupants: Discomioit, loss of concentration and
health deterioration.
On equipment: Erratic performance, low reliability and equipmeni failure.
5.3.3 Psychrometry
Psychrometry is the science that deals with ihe properties of air and water
vapour mixtures. The gases present in atmospheric air and the psychrometric
properties of air are discussed. These properties are shown schematically on
the psychrometric chari.
Atmospheric air consists of a large number of gaseous components such as
oxygen, nitrogen, argon, neon, carbon dioxide, carbon monoxide, chlorofluoro
carbons (the so-called ozone depletion gases), water vapour, dusi, pollen,
odours, and poisonous and toxic contaminants, (Shuttleworth, 1983).
In the air-conditioning field however, air is regarded as a mixture of dry air and
water vapour. The study of the behaviour of dry air and water vapour ! nixiures
is known in scientific terms as psychrometry.
The psychroinetric properties of air which are of interest in AC sysiems, are: Dry bulb temperature
Wet bulb temperature
Relative humidity
Specific humidity
Specific volume
Enthalpy
VOLUME 1
The above psychrometric terms are defined as follows:
Dry bulb temperature (DB)
Dry bulb temperature is the temperature measured on a ihermometer with a
mercury or alcohol bulb which is dry on the outside. The unit of measurement
of Toe is degrees Centigrade (°C).
Wet bulb temperature (TWB)
Wei bulb temperature is the temperature measured on a thermometer which
has its mercury or alcohol bulb covered by a moist cloth. The unit of
measurement of Two is degrees Centigrade (°C).
Relative humidity (RH)
Relative humidity is the degree of saturation of a dry air and water vapour
mixture. iviathematically, RH is expressed as the ratio of the vapour pressure
io the saturated vapour pressure:
RH =
PvaP
vapour
sat
where Pvapour is ihe vapour pressure and Psat is the saturated vapour
pressure. RH is dimensionless, in other words, it has no unit of measurement.
li is, however, more conveniently expressed as a percentage. RH can vary
from 0% (for completely dry air) io 100% (for completely saturated air).
Dew point temperature (Top)
Dew point temperature is any temperature where ihe dry bulb temperature
is equal to the wet bulb temperature. This occurs at saturation, i. e. where
the RH is 100%. At any condition where the RH is less than 100%, TOB
will always be higher than TWB. The unit of measurement of Top is
degrees Centigrade (°C).
Specific humidity (SH)
Specific humidity is the mass of water vapour contained in 1 kg of dry air.
In mathematical terms, SH is expressed as the mass of water vapour per
unit mass of dry air:
SH
mvapourma
where
mvapouris the inass of water vapour and ma is the mass of dry air. The
unii of measurement of SH is kilogram per kilogram of dry air (kg/kg a). The
mass of water vapour present in air is relatively small, but is nonetheless
significani, since it plays a major role in factors like human comfort.
Specific volume (SV)
Specific volume is the total air volume (i. e. the dry air volume plus the water
vapour volume) per unit imass of dry air: Vair + Vvapour
SV =
mair
The unit of measuremeni of SV is meire cubed per kilogram (in3/kg).
Enthalpy (h)
Enthalpy gives an indication of the total heat present in air, and is
mathematically expresseci as the heat per unit mass of dry air:
h=
Heat
ma
The unit of measurement of enthalpy is joule per kilogram of dry air (J/kg a).
Vapour pressure
Vapour pressure is the partial pressure of the water vapour component of air.
Like specific humidity, it is a relatively small quantity, but is not negligible. Theunit of measurement of
vapour pressure is Pascal (Pa).
The psychrometric properiies of air defined above can be shown together on a
diagram, known as the psychrometric chart. A diagrammatic representation of a
psychrometric chart is shown in figure 5.21.
Constant relative humidity
Constant specific humidityand
Constant vapour pressure
Saturation: RH = 100%, Top - Twe
Constant specific volume
Constant dry bulbtemperature
Constant
wet bulb
temperatureand
Constant
enthalpy
Figure 5.21 Diagrammatic representation of a psychrometricchari
Note that the magnitudes of air properties are dependent on the altitude above sea
level (ASL). The air properties required for the design of an AC plant in Cape Town,
for instance, must be obtained from a psychrometric chart specifically compiled
for sea level, while a psychrometric chart for 1 400 m ASL must be used for the
air properties in Pretoria.
5.3.4 Human comfort
Human comfort may be influenced by factors as diverse as noise, aesthetics,
illumination, wind speed, duist content, air temperature and air humidity.
Comfort can be accomplished by controlling these factors to suit the differeni
inclividual comfort requiremenis. While air-conditioning will fail in controlling
illumination and aesthetics, it will more effectively control factors such as dust
content, air temperature and huinidity. An air-conditioning system is generally
required to meet the following comfort criteria (Shuttleworth, 1983):
To supply light air motion
Human beings are sensitive to the surrounding air speed. As a resuli, air
speed must be controlled within a range of 0,1 m/s to 0,25 m/s.
To maintain a suitable dry bulb temperature in an occupied space
Human beings are sensitive to iemperature changes. Temperaiure changes
of as little as 1 °C can be felt. Generally, temperaiures between 22,5 °C and
25 °C can be considered comfortable, according to the American Society of
Heating, Reirigeration and Air-conditioning Engineers (ASHRAE).
To maintain a suitable relative humidity
Humans are not particularly sensitive to relative humidity changes. Reiative
humidities between 20% and 60% can be considered comfortable, according
to ASHRAE.
To supply clean air
Air wirich is non-toxic, non-poisonous, odour free, and which has a low dust,
pollen and smoke content, can be considered “clean”.
To help peopie lose their metabolic heat
Human metabolic heat depends on two factors, inamely the level of activity
and the surrounding air temperature. A person working in an office with a
iemperature of 20 °C, will generate approximately 140 W of heat, while the
metabolic rate of a person dancing in a room with a temperature of 26 °C,
will be approximately 265 W (Jones, 1982).
Note that human comfort may difier from country to country and from season
io season. The above criteria can therefore only be considered as a guideline.
5.3.5 Heat, heat sources and heat transfer mechanisms inbuildings
Heat
The two types of heai encountered in the analysis of AC energy requiremenis,
are sensible heat and latent heat: Sensible heat is transferred in the absence of any change in specific
humicity, and is generally associated with a change in dry bulb
temperaiure. See figure 5.22.
Latent heat is transierred in the absence of any change in dry bulb
temperature, and is generally associated with a change in specific
humidity. See figure 5.23.
Hih
Тов1
TDB2
Figure 5.22 Sensible heat transfer
2
1
Това - Това
Figure 5.23 Latent heat transfer
SH, - SH,
SH2
SH,
From figure 5.22 it can be seen that, in a sensible heat fransfer process,
the dry bulb temperature increases from TDB1 io TDB2 , while the specific
humidity stays constant. Figure 5.23 shows ihat, in a latent heat transfer
process, the specific humidity increases from SH, to SH2 , while ihe dry
bulb temperature stays constant.
Heat sources in buildings
(a) Sources oí sensible heat in buildings include the following:
Transmission heat
Transmission heat transfer occurs due to a temperature difference
between outside and inside. This temperature difference causes heat
io flow from the outside to the inside in summer and from the inside to
the outside in winier. Transmission heat is the heat transmitted through
building structural components such as walls, windows, ceilings and
roofs.
Solar heat
Solar heat enters the building through windows and tire building structure.
The heat may have an immediate effect, such as on a person sitting in
front of a window, or may be absorbed by the struciure to be released
later.
Solar radiation is transferred to a building in three ways:
Directly from the sun
Indirectly, through scattering by clouds
Indirectly, by reflection from surrounding surfaces
Sensible heat eniry due to fresh air supply
When the fresh air cry bulb temperature exceeds the room dry bulb
temperature, sensible heat is added to the room air.
Lighting
Light adds heat to room air. Lighting heat depends on the type of lighting,
and may well constitute the largest segment of the cooling load. Light
performance is normally expressed in terms of illumination per power
input in lumens per watt. Table 5.13 from Shuttleworth (1983), gives the
light output for different types oí lamps:
Table 5.13 Light output of different lamp types
Type of lamp
Incandescent
Tungsten halogen
Fluorescent
: viercury vapour
ivetal halicie
Sodium vapour
Equipment
Light output
(lumens/)
12-20
12-16
72-88
30-60
50-90
100-105
iviechanical, electrical and electronic equipmeni add sensible heai to
room air. Examples are:
BUILDING PRACTICE - VOL. UME 1
Production machinery, e. g. in a factory
Copiers and computers
Telecommunications and radio equipment
Fan motors
Domestic appliances, such as hair grooming equipment, kettles,
urns and stoves
Letier sorting machines
Human metabolism
Human sensible heat depends on the room dry bulb teinperature and
level of physical activity. Table 5.14 from Jones (1982) gives the human
sensible metabolic heat for different temperatures and activities.
Table 5.14 Human sensible metabolic heat vs. To DBvarious activities
Activity
Seated at rest
Office work
Standing
Eating in a restaurant
Light factory work
Dancing
90 W
100 W
105 W
110 W
130 W
140 W
22 °C
80 W
90 W
95 W
100 W
115 W
125 W
24 °C
75 W
80 W
82 W
85 W
100 W
105 W
for
25°C
65 W
70 W
72 W
85 W
80 W
90 W
From table 5.14 it can be seen thai sensible metabolic heal increases
with activity and decreases with room dry bulb temperature.
(b) Sources of latent heat in buildings are:
Kettles
When water is boiled in a keiile or urn, latent heat of vaporisation is
acided to the room air.
Human metabolism
Human latent heai depends on the room cry bulb teinperature and level
of physical activity. Table 5.15 (Jones, 1982) gives the hunan lateni
metabolic heat for different tenperatures and activities.
Table 5.15 Human latent metabolic heat vs. Tos forvarious activities
Activity
Seated ai rest
Office work
Standing
Eating in a restaurani
Lighi iaciory work
Dancing
20 °C
25 W
40 W
45 W
50 W
105 W
125 W
22 °C
35 W
50 W
55 W
60 W
120 W
140 W
24 °C
40 W
50 W
68 W
75 W
135 W
160 W
26 °C
50 W
70 W
78 W
85 W
155 W
175 W
From table 5.15 ii can be seen that latent metabolic heai increases with
activity and increases with room dry bulb temperature.
Latent heat entry due to fresh air supply
When the fresh air wet bulb temperature exceeds the room air wei bulb
temperature, latent heat is added to the room air.
Moisture migration
Building structures are porous, allowing moisture to migrate through the
structure into the room air. iMoisiure can also enter the building through
leaking window frames and cracks in structural components.
Heat transfer mechanisms
The three mechanisms of heat transfer are conduction, convection and
radiation.
Conduction heat transfer
Concluciion heal transier occurs when a temperaiure difference exists in
a solid, or when two solids at different surface temperatures are in contaci
with each other. In building materials, heat is conducted through solid
structural components such as walls and roofs.
The heat flow depends on the following factors: The area of structural component: The larger the area
of the
component, the higher the heat transier.
The temperature difference in the component: The larger the
temperature difference, the higher the heat transfer.
The thickness of the component: The thicker the component, the
lower the heat transfer.
The thermal conductivity of the component: The higher the
thermal conductivity, the higher the heat transfer. Typical thermal
conductivities of building materials, from Holman (1976), Stoecker
and Jones (1982) and Martin and Oughton (1989), are given in
table 5.16.
Table 5.16 Typical thermal conductivities of buildingmaterials
Building material
Common brick
Face brick
Concrete (1 900-2 300 kg/m3)
Lightweight concrete (600 kg/m3)
Portland cement
Plaster
- Terrazzo lile
Window glass (2 500 kg/m3)
Wood (Fir)
Plywood
Chipboard
Hardboard
Polyurethane board
Loose glass fibre
Thatch straw
Thermal conductivity(W/m °C)
0,69
1,32
1,37
0,19
0,29
0,48
1,75
1,02
0,11
0,14
0,11
0,20
0,02
0,04
0,07
Convection heat transfer
Convection heat is iransferred through air motion. In buildings, an air
film forms on the surface of a building structural component, such as a
wall or roof. The heat transferred through the film is calleci convection
heat transfer. The convection may occur naturally, such as when the air
is cooler than the surface, or may be forced, such as when the winci
blows. The faster the air moves, ihe higher the convection heat transfer.
Radiation heat transfer
Radiant heat is transferred from one surface to another if the two surfaces
are at different temperatures. The radiation depends or the temperatures
and absorbtivities of the iwo surfaces. An important radiation heat transfer
parameter affecting human comfort, is the so-called mean radiant
temperature (MRT). The MRT oí a room is defined as the weighted
average of the surface temperatures in the room (Shuttleworth, 1983).
The MRT can be mathematically expressed as:
MRT =
n
ΣΑ,Τ;
i=1
n
ΣΑ;
i=1
where n is the number of surfaces, A; is the area of a surface and Ti
is ihe temperature of the suriace.
For a room with a floor, ceiling, and four walls, the total number of
suriaces is 6. The miRT of the room surfaces is obtained as follows:
MRT =
Afloor floor + Aceiling ceiling + Awallt Twall1 + Awall2Twall2 + Awał3wall3 + Awall4+wal4Afloor +
Aceiling + Awall1 + Awall2 + Awall3 + Awall4
As an example, consider a room with the following wall, ceiling and
floor temperatures and areas:
Component
Area (m2)
Temperature (°C)
Floor Ceiling Wall 1 Wall 2 Wall 3 Wall 4
20
20
20
26
12
23
15
23
12
23
15
23
The iviRT of the room suriaces, using the equation shown above, is 23 °C.
5.3.6 Refrigeration and the refrigeration cycle
The total heat generated in a building must be removed and rejecied to the
environment. This is accomplished by ineans oí a refrigeration system.
Refrigeration takes place in a closed loop, or cycle, called the refrigeration cycle.
A schematic layout of tie refrigeration cycle is shown in figure 5.24.
Refrigerant liquid
High T, P
Condenser
mm
Outside air
Expansion mechanism
Evaporator
Refrigerantliquid
Low T, P
Room air
int
High T, P
Refrigerant gas
Discharge side
Compressor
Suction side
Refrigerantgas
Low T, P
T = temperature, P =pressure
Figure 5.24 Schematic layout of the refrigeration cycle
The system consists of four major components, i. e. an evaporator, a compressor,
a condenser and an expansion device. A cooling substance, krown as the
refrigerant, is circulated through the system in a closed loop. The refrigerant
absorbs room heat at low temperature and low pressure, and rejects it to the
atmosphere at high temperature and high pressure. Heat absorption from the
building takes place in the evaporator, while heat rejection to the atmosphere
takes place in the condenser.
The compressor serves two purposes. Firstly, it provides power to circulate the
refrigerant, and secondly, it raises the temperature of the refrigerant from the low
evaporation temperature to the high condensing temperature. The suction side
of the compressor is connected to ihe evaporator, while the discharge side is
connected to the condenser. The expansion device, which can either be a long,
thin (capillary) tube or an expansion valve, lowers the refrigerant iemperature
from condensing temperature to evaporation temperature.
5.3.7 Air-conditioning system classification
According io Shuttleworth (1983), air-conditioning systems can be classified in terms
of 3 criteria, namely: Position, or placement, of tine system
Type of cooling system
Type of temperature control system
Classification in terms of position, or placement, of the system
The following two broad categories exist: Central AC systems
Local AC systems
Gentral AG systems
In central AC systems, the AC units are installed in a remote location,
i. e. away from the rooin. Such AC systems are also called central AC
plants.
The supply air is conditioned in the plant room and transported to the
room via a supply air duct, after which it is returned to the plant via a
return air duct. Fresh air is added at the plant. A schematic layout of
central AC system is shown in figure 5.25.
Outside air
Return air
AC plantroom
Supply air duct
Conditioned air
Return air at
room temperatureand humidity
Return air duct
Room
Relief air
Figure 5.25 Schematic layout of a central AC system
The advantages of ceniral AC systems are: High efficiency
The majoriiy of system components are located in one room (the
plant room), thereby facilitating maintenance
Relatively few components to maintainDue to remoteness of the plant room, operation can be very
quiet
The disadvantages of central AC systems are: Control of individual room conditions may be inaccurate,
especialiy
where large variations in room heai loads are experienced
Ducting increases system installation cost.
Local AG systems
In local AC systems, each room in the building is air-conditioned by its
own small AC unit. All the functions of the central AC system are carried
out in the local unii. A schematic layout of a local AC system is shown
in figure 5.26.
The advantages of local AC systems are: Room conditions can be controlled individually
AC units can be added and removed from rooms with relative
ease, and without interfering with the operation of the rest of the
plant
Selective installation, i. e. only in rooms where AC is required,
reduces initial cost
Outside air
AC unit
Return air
Condition
Room 1
Relief air
Outside air
air
AC unit
Return air
Conditioned air
Room 2
Relief air
Outside air
AC unit
Return air
Conditioned air
Room 3
Relief air
Figure 5.26 Schematic layout of a local AC system
The disadvantages of local AC systems are: High maintenance cost due to large number of components
Maintenance must be done in each room, which may be
inconvenient and may be difficult to schedule
The life expectancy of local systems is generally shorter ihan ihai
of ceniral systems
Classification in terms of the type of cooling system
Two broad caiegories exist, namely direct expansion (DX) systems and chilled
water (CW) systems.
Direct expansion (DX) systems
Direct expansion systems make use of the room air to directly evaporaie
the refrigerani. The room air heat is irar: sferred to the refrigerant by
means of a heat exchanger (the evaporator). As the air passes through
the evaporator, it is cooled down and the refrigerant is evaporated. A
schematic layout of a DX system is shown in figure 5.27. The system
also consists of air-handling equipment such as an air louvre to control the
air flow, a filter to ciean the air, a heater to heat the already conditioned
air, and a fan. The refrigeration system consists of the normal refrigeration
cycle coinponents, i. e. a compressor, condenser and expansion
mechanism. See also figure 5.24.
Condenser
Expansion
mechanism
Fan
Heater
Evaporator
Filter
Grille
Supply air
Compressor
Figure 5.27 Schematic layout of a direct expansion system
The advantages of DX systems are: System simplicity, due to direct evaporation. Only one heat
exchanger
is required io transfer heat from the air io the refrigerant
Low initial cost
The disadvantage of DX systems is that the control of system cooling
capacity may not be as accurate as in the case of CW systems.
Chilled water (GW) system
In a chilled water system, ihe air is cooled by chilled water via a heat
exchanger, known as the cooling coil. The water, in turn, is cooled in
another heat exchanger, which acts as the evaporator. As the water
passes through the evaporator, the water is cooled, or chilled, and the
refrigerant evaporates in the heat exchanger. A schematic layout of a CW
system is shown in figure 5.28. The system also consists of air-handling
equipment, such as an air louvre to control the air flow, a filter to clean
the air, a heater to heat the already conditioned air, and a fan. The
refrigeration system consists of the normal refrigeration cycle components,
i. e. a compressor, condenser and expansion mechanism. See also
figure 5.24. The part of the refrigeration system responsible for cooling
the water, is known as the chiller. A water pump is required to circulate
the water through the system.
CW systems have the advantage that more accurate control of system
cooling capacity can be accomplished than in the case of DX systems.
The disadvantages of CW systems are: CW systems are more complicated than DX systems
The installation cost of a CW system is higher than that of a DX
system
Waier treatment may be required, depending on the quality of the
water
Chiller
Fan
Heater
Cooling coil
Filter
Grille
w
Supply air
Intake air
Air handling unit
Water
pump
Heat exchanger (evaporator)
CompressorExpansion
mechanism
Condenser
Figure 5.28 Schematic layout of a chilled water system
Classification in terms of the type of temperature control system
Three categories exist: Constant air volume, variable temperature systems
Constant temperature, variable air volume (VAV) systems
On-off control
Constant air volume, variable temperature systems
A constant air volume AC sysiem supplies a fixed volume flow of air to
the room, irrespective of the heat load. Room climatic conditions are
controlled by varying ihe supply air temperature. Where multiple rooms
are to be supplied from one plant, the supply air temperature will be the
same for all the rooms.
For a given room temperature and load fractior., the required supply of
air temperature can be obtained by the following equation:
!
Ta
T;
100
(T; - Ts)
where Ta is the required supply air temperature, T; is the desired room
temperature, a is the heat load fraction (as a percentage) and Ts is the
full load supply air temperature.
Consider, for instance, a room with a desired temperature of 22 °C andfull-load supply air temperature
of 12 °C. If the load is halved, the
required supply air temperature, from the equation shown above, will
be 17 °C. Similarly, for a load fraction of 25%, the required supply air
temperature is 19,5 °C.
The advantages of constant volume, variable temperature systems are:
Simplicity of operation
Relatively low costHigh popularity and often used
The disadvantage of a constant volume, variable temperature systein is: Where large differences in heat
loads exist between zones or rooms,
ihe supply air temperature will be too low for certain zones and too
high for others, causing discomfort to occupants.
Constant temperature, variable air volume (VAV) sysisni
A variable air volume (VAV) system supplies air to the room at a constant
temperature, and changes the supply air flow according to the load.
Where multiple rooms are io be supplied from one plani, each room
receives the correct volume of air to provide proper cooling. Air flow is
controlled at the air outlet into ihe room.
For partial-load conditions, the required supply air flow is obtained as
follows:
Va aVs
where Va is the required air flow under partial load conditions, a is tie
load fraction and Vs is the full-load air flow. It can be seen from the
above equation that, for VAV systems, supply air flow is directly
proportional to load.
The advantage of VAV systems is that each zone in őre building will
receive the correct volume of air to cool that particular zone, irrespective
of the load.
=
The disacivantages of VAV systems are: During low heat loads, such as in winter, the air supply will be
low.
This may result in a lack of fresh air for occupants and may cause
drowsiness.
The system is more expensive ihan constant temperature systeins.
On-oft control
On-off AC temperaiure control systems switch on if the room temperature
rises above a maximum allowabie value and switches off if the
temperature drops below a minimum allowable value. The system inay
for instance switch on if ihe temperature rises above 24 °C and switch
off if the temperature crops below 20 °C.
The advantages of on-off control systems are:
Simplicity of operation
Low cost due to simplicity
The disadvantages of on-off control systems are:
Temperature control is not very accurate
Switching the plant on and off inay shorten the life of certain
components, such as the compressor motor
5.3.8 Ventilation and filtration
Ventilation
The reasons for fresh air supply io buildings are given as follows by Jones
(1982):
To satisfy the oxygen needs of occupants
To dilute odours to a socially acceptable level
To dilute the concentration of carbon dioxide to a satisfactorily low level
The rate of fresh air supply depends on the occupation of a room or building
and the application. Recommended values of fresh air supply rates to various
kinds of buildings, from Jones (1982), are given in table 5.17.
Table 5.17 Recommended fresh air supply rates for variousbuilding types
Building type
Private nomes
Board rooms
Cocktail bars
Departmeni siores
Factories
Garages
Operating theatres
Hospital wards
General offices
Private offices
Restaurants
Theatres
Fresh air supply(1/s/person)
8-12
18-25
12-18
5-8
8-12
5-8
8-12
12-18
5-8
Fresh air supply(1/8/m2)
0,8
8,0
16,0
1,3-2,0
1,3-2,0
The two basic ventilation system iypes encountered in buildings are natural
ventilation systems and forced ventilation systems.
Natural ventilation systenis
Natural ventilation systems make use of wind and natural convection to
produce air flow in a building. Outside air enters the building through
grilles, louvres, windows and doors. The aperture areas of these
openings can be adjusted, either manually or automatically, to alter air
flow through ihe building. The main advantages of natural ventilation
systems are:
simplicity of operation
high energy efficiency
low cost
The disadvantages of natural ventilation systems are: Insufficient flow in buildings with high flow
resistances, e. g. where
long ducts are required to provide air passage to remoie rooms.
Flow control may be inaccurate, e. g. where wind speeds vary widely.
The abovementioned disadvantages can be overcome by means of
forced ventilation systems.
Forced ventilation systems
Forced ventilation systems make use of fans, cucts and louvres to supply
fresh air to spaces. Outside air is filtered in order to remove dust and
other contaminants. A fan is used to sufficiently raise the air pressure
to overcome the upstream and downstream resistance of the ventilation
system components, such as ducts, inlet louvres and outlet louvres.
Air filtration
Air is filtered to remove the following contaminants (Jones, 1982):
Dusts(diameter < 100 um)
Fumesdiameter < 1 um)
Smokes (diameter < 1 km)
ivists and fogs (diameter < 100 um)
Vapours and gases: Vapours can be removed by cooling below thedew point, but gases cannot.
Organic particles: - Bacteria (diameter 0,2 to 5 um)- Pollen(diameter 5 to 150 um)
- Spores of fungi (diameter 1 to 20 um)
Viruses(diameter < 1 um)
Fiiters are required to remove the above contaminants from the air, and to let
the purified air through. It must be emphasised that no filier can remove all
contaminants, therefore particles smaller than a ceriain diameter will always
be let through with the air.
Filter performance is expressed in terms of the following criteria:
Efficiency
The weight of conta. ninants removed per iotal contaminant weigiit preseni
in the air. The higher the efficiency, the better. It must be noted ihat
diriy filters are more efficient than clean filiers.
Dust holding capacity
The maximum weight of contaminants that can be retained by the filter.
As the filter gets cirtier, the mass of contaminants collected by the filter
increases. The filier must not tear or let some of the contaminants
escape back into the purified air.
Pressure drop
In order to remove contaminants, the filter creates a flow resistance,
thereby lowering the air pressure. The lower the flow resistance, the
better.
Three major filter types used in air-conditioning systems are: Bag-type filters
Automatic roller-type fabric filters
Panel filters
The three filter types are shown schematically in figure 5.29.
All the above filters are dry filters. Wet filters, like washers and scrubbers, are
largely used for the absorption of soluble gases, and are not coinmonly used
for solid particle filtering (Jones, 1982).
Other filter types include cyclone filters and electrostatic filters. Cyclone filters
operate on the principle of spinning air, like in a cyclone. The contaminants,
which are heavier than air, are swung to the outside and separated from the
purified air.
Electrostatic filters are a more sophisticated type of filter. Electrostatic filters
make use of plates oppositely charged to the dust, thereby attracting dust
and separating it from the purified air.
Contaminated air
Filter frame
Fabric bags
N.
Purified air
Bag filter
Clean filter material
Contaminated air
Dirty filter material
Contaminated air
Filter panel
Filter
element
Purified air
Roller
Panel filter
Purified air
Roller
Automatic roller-type fabric filter
Figure 5.29 Schematic layout of three filter types used in ACsystems
5.3.9 Ducting and fans
Ducting
Ducting is required to guide supply air to the room, while the ían is required
io force ihe air through the ducting system. Tire ducting system may include
filters, inlet and outlet louvres and ducting equipment such as bends (or
elbows), branches and guide vanes. Bends are required to change the flow
direction, while branches are required to suppiy air io more than one roon.
Guide vanes are normally installed inside a bend to reduce pressure and flow
losses in the bend. An example of a ducting system is shown in figure 5.30.
90° elbow
Guide vanes
Duct
Supply air
Duct inlet at fan;
Air pressure = PlusAir flow = Vi
(V)
Louvre
Room;
Air pressure = Proom
Air flow = V2
Figure 5.30 Example of a ducting system
Supply air
Louvre
The duct inlet is connected to a supply fan. Downstream of the fan, the
direction of the air flow is turned through 90° by imeans of an elbow. Guide
vanes are installed in the elbow to smooth the flow in order to reduce flow
losses. The duct has two outlet louvres. The first branches off to the side
of the duct to supply air with a ilow of V, to a room, while the air flow at the
second outlet at the end of the duct is V2. The total air flow Vy provided by
the fan is equal to the flow required at the two outlets:
V1 = V tan
1
V1 + Va
The pressure drop in the ducting system is equal to the fan pressure. The
pressure drop in the ciucting system is the sum of ine pressure drops of the
duct components:
Pstraight sections + Pbend + Plouvre
where P duct is the pressure lost in the duct, Pstraight sectionsis the pressure
lost in the straight sections and Plouvre is the pressure lost through the outlet
louvre.
Pduct
The relationship between the air flow in the duct and the pressure loss is:
(a) Pduct Q (V1)2
From the above equation, it can be seen that the pressure loss in the duct
is directly proportional to the flow squared. The pressure loss in the duct
equals the fan pressure:
(b)
Plan
- Pauct
For the sake of clarity, the two equations shown above are summarised
graphically in figure 5.31. The duct pressure lost vs. flow curve, or duct
resistance curve, is a graphical representation of equation (a). The fan curve
iniersects the duct resistance curve in the operating point, where the duct
flow equals the fan flow and the duct pressure loss equals the fan pressure.
The fan curve depends on the type of ian used, e. g. axial flow or centrifugal
flow, with forward curved or backward curved blacies. For the applicable duct
and fan (a forward curved centrifugal flow fan), the flow is 12 m3/s. The fan
pressure, which equals the pressure loss in the duct, is 0,9 kPa, or 900 Pa.
Fans and fan characteristics will be covered in more detail in the next
paragraphs.
Pressure (kPa)
1,8
1,6
,4
,2
1,0
0,8
0.6
0,4
0.2
0
Duct resistance curve
Fan curve
Operating point
2
4
6
8
10
12
Air flow (m3/s)
14
16
18
Figure 5.31 Pressure vs. flow characteristics of a duct andfan system
Fans
Fans are used to supply forced ventilation in AC systems of buildings. Fans
add energy io the air current by increasing air pressure. This is done in order
to overcome the pressure losses in the air supply system, consisting of filters,
ciucts and inlet and outlet louvies.
The two fan types most commonly used in AC systems are axial flow fans
and centrifugal flow fans.
Axial flow fans
In axial flow fans, both the air iniet and outlei are in the direction of the
axis of the ian. Axial flow fans are sometimes mounted in a duct to guide
the air flow. Fan blacles are shaped in the form of aerofoils. A schematic
drawing of an axial flow fan is shown in figure 5.32.
Duct
Outlet
Inlet
Fan blade
Figure 5.32 Schematic drawing of an axlal flow fan
The acivantage of an axial flow fan is that very good space utilisation can
be obtained, especially where low fan pressure is required.
The disadvantage of an axial flow fan is that in comparison with
centrifugal flow fans, axial flow fans cannot generate high pres dres,
Centrifugal slow fans
Two types of centrifugal flow fans, i. e. forward curved centrifugal (FCC)
and backward curved centrifugal (BCC) fans are used in AC systems.
In FCC fans, the blades are curved forward, in the direction of rotation,
while in BCC fans, the blades are curved backward.
Blades are curved forward or backward to obtain a desirable pressure
vs. flow characteristic. Schematic drawings of FCC and BCC fans are
shown in figure 5.33, while the pressure vs. ilow characteristics of the
iwo ían types are shown in figure 5.34.
Air
in
Air
out
Forward curved
blades
Forward curved centrifugal
Air
in
2
Air
out
Backward curved
blades
Backward curved centrifugal
Figure 5.33 Schematic drawings of FCC and BCC fans
Fan pressure
Forward
curved
centrifugal
Fan pressure
Backward
curved
centrifugal
Air flowAir flow
Figure 5.34 Fan pressure vs. air flow characteristics ofFCC and BCC tans
The advantages of centrifugal fans are:
A number of different fan wheel, or impeller, sizes can be selected
io suit the pressure and flow requiremeni.
In the case of duct alterations, the motor can be changed with
relative ease. This is made possible by connecting the fan andmotor via a belt drive.
The disadvantage of a centrifugal fan is that in order to obtain the flexibility
of using a range of impeller and motor sizes, centrifugal fans can be very
large
FCC fans are generally smaller than BCC fans. BCC fans are mechanically
more efficient, in the order of 80% to 85% vs. 60% to 70% for FCC fans
(Daly, 1978).
5.3.10 Air outlets and inlets (Shuttleworth, 1983)
Air outlets are requires to properly control and distribute air flow in the room.
Outlets are mounted in openings at the ends of supply air ducts or duct branches.
The three main purposes of outlets are: To control the supply air volume ilow
To direct the flow into the roomTo improve the appearance of the opening
Inlets are required to allow air into AC plant rooms or return air ducis. Iniets have
wo main purposes, namely:
To control the inlei air volume flow
"To improve the appearance or the opening
TD
Contrary to outlets, inleis are not required to direct flow.
The main types of air outlets and inlets are grilles and louvres. Grilles have
adjustable blades to increase the flow area and change the flow direction, while
louvre blades have fixed aperture areas and flow angles.
The geometric and performance criteria of outlets and inleis are:
Aspect ratio
Induction ratio
Throw
Drop
Air change
Smudging
The definitions of the above criteria are:
Aspect ratio (AR)
Aspect ratio is the ratio of maximum dimension to the minimum dimension
of the outlet or inlet. The two important dimensions of outlets and inlets are
width and height. If width exceeds height, the aspect ratio is:
AR
b
h
where b is width and h is heigint. li height exceeds width, the aspeci ratio is:
AR
h
b
Induction ratio
Air is supplied to ihe room via the outlei. The supply air mixes with the room
air and also sets the room air in motion. This phenomenon is known as
induction. The supply air is known as primary air and the room air is known
as secondary air. The inciuction ratio is the ratio of ihe primary air flow plus
the secondary air flow to the primary air flow: Q+Q2
Induction ratio
=
01
where Q , is the primary air flow and Q zis the secondary air flow.
High induction ratios are required to prevent dead spois and draughts.
Outleis with high AR ratios normally have high induction ratios.
Throw
Primary air slows down as it travels through the room. The position, relative
to the outlet, where the air speed has decreased to a value of 0,25 m/s, is
known as the throw. The position is normally the distance from the outlet to
the opposite wall, plus the distance from the ceiling to a height of 2 m above
floor level:
Throw = 1, + 12
where l is the distance from the outlet to ihe opposite wall and Iz is the
distance from the ceiling to 2 m above floor level. The throw of ar outlet is
schematically shown in figure 5.35.
Duct
Section through room
Primary air
Floor level
Figure 5.35 Throw of an outlet
ly
0,25 m/s
₂
2m
Drop
Drop is the height between the height of outlet and the heigiit above floor
level where the air speed has decreased io 0,25 m/s. The drop of a ceiling
mounted outlet is schematically shown in figure 5.36.
Section through room
Duct
Drop i
2m
Figure 5.36 Drop of an outlet
-0,25 m/s
Floor level
BUILDING PRACTICE - YOLUME 1
Air change
If all the air in a room is removed and replaced, one air change has occurred.
An air change is usually expressed per time unit, e. g. per hour. ivost
ventilation systems provide 6 to 15 air changes per hour.
Smudging
The secondary air flow in a room causes gust deposits on the perimeter of
an outlet. This is called "smudging" in AC terms. The dust deposits can be
removed by installing a washable, removable "smudge ring" around the
perimeter of the outlet. The ring is removed and washed during periodic
servicing of the entire AC plant.
Outlets are produced in different shapes for differeni purposes, and can supply
air in different directions. Outlet direction can be horizontal, as in figure 5.35,
or vertical, as in figure 5.36. The most popular vertical configurations are: Rounci, with radial outlet
Linear, with one or two outlet directions. Linear outlets provide high
induction ratios.
Square, with one, iwo, three or four outlet directions
Rectangular, with one, two, three or four outlet directions
5.3.11 Refrigeration equipment
The three types of refrigeration equipment that will be discussed, are cooling coils
(evaporators and chilled water coils), compressors (reciprocating compressors and
kinetic compressors), and condensers and cooling towers (air-cooled condensers,
evaporative condensers and cooling towers).
Cooling coils
A cooling coil consists of a coil wound through a core, with fins parallel to
the flow direction. Air moves througin the core, between the fins, and rejects
heat to the cooling medium, which passes through the coil. The coil can have
more than one row. Generally, the higher the number of rows, the lower the
sensible heat ratio of the coil. Rows are normally added to increase the latent
heat capacity of a coil. The purpose of the fins is to improve heat transfer
between the air and cooling medium. The coil is usually made of copper,
while the fins are made of aluminium. A schematic layoui of a cooling coil is
shown in figure 5.37.
Cool air out
Cooling medium in
Cooling medium out
Coil tube
Warm air in
Cooling fin
Figure 5.37 Schematic layout of an AC cooling coil
Two iypes of cooling coils are used in AC systems, depending on the system
type. In DX systems, the coil is an evaporator, while in CW systems, the coil
is a chilled water cooling coil. In evaporators, the cooling medium is a
refrigerant. The refrigerant enters the coil as a liquid, evaporates in the coil
due to the heat being transferred from the air, and leaves the coil as a gas.
The difference between evaporator coils and chilled waier coils, is that in the
latter, the cooling medium, is water instead of refrigerant. Water enters the
coil at a low temperature, gains heat from ihe air passing through the core,
and leaves the coil at a higher temperature. The chilled water is supplied to
the coil by the chiller. The warm water leaving the coil, is pumped back to
the chiller, where the heat is rejeciec. Note that, contrary to evaporators
where the refrigerant changes from the liquid state to the gaseous state, the
state of the water does not change.
Gompressors
The two major AC compressor iypes are positive displacement compressors
and kinetic compressors.
Positive displacement compressors
The principle of operation of a positive displacement compressor is as
follows. Refrigerant is let into the compression space from the evaporator
through an inlet valve mechanism. As soon as the compression space
is filled, the inlet valve closes and traps ihe refrigerant inside. A movable
mechanism, such as a piston, compresses the refrigerant until the desired
discharge pressure is reached. In reciprocating piston compressors, the
piston is driven by a motor via a rotaiing crankshaft and connecting rod.
When the pressure inside the compression space reaches discharge
pressure, an exhaust valve mechanism opens and lets the refrigerant out
and into the condenser.
The compression ratio of a positive displacement compressor is
independent of the rotating speed of the crankshaft, and only depends on
the ratio of the maximum value of the compression space volume to the
minimum value of the compression space volume. Both the inlet and exhaust
valves are of the reed type: as soon as the refrigerant pressure exceeds
a pre-set value, the valve physically bends and exposes the inlet or outlet
port, thereby releasing the refrigerant gas.
Reciprocating compressors can have as few as one and as inany as
sixteen cylinders. Crankshaft rotating speeds vary from 1 750 revolutions
per minute (r. p. m.) to 3 500 r. p. m. The modern trend is to directly connect
the inotor to the compressor, thereby eliminating costly transmission
systems. Furthermore, during manufacture, small compressors are
hermetically sealed to curb refrigerant leakage, (Shuttleworth, 1983).
A number of positive displacement compressor types are found in AC
systems. The most popular type, i. e. the reciprocating piston compressor,
is shown in figure 5.38. Other positive displacement compressor iypes
are the:
rotary vane type
rolling piston iype
rotary screw type
scroll type
Suction
One-way valve
Compression space
Piston
Discharge
Connectingrod
Crankshaft
One-way valve
Figure 5.38 Schematic layout of a positive displacement, reciprocating piston compressor
Kinetic compressors
Centrifugal compressors operate on the principle of raising refrigerant
pressure by adding kinetic energy to the refrigerant. Compression is
brought aboui by a rotating hub with radially curved blades attached to
the hub. This is known as the impeller. Centrifugal compressors require
no valves to trap the refrigerant inside the compressor, and operate on
a continuous flow process. The faster the impeller spins, the higher the
discharge pressure. A centrifugal compressor is schematically shown
in figure 5.39.
Centrifugal compressors are mainly used in larger AC systems. The
vibration levels of cenirifugal coinpressors are lower than those of
reciprocating compressors, but discharge pressures are lower.
Suction
Impeller
Discharge
Figure 5.39 Schematic layout of a kinetic, centrifugalGompressor
The following five methods can be applied to control compressor cooling
capacity:
Hot gas bypass
The not discharge refrigerant gas is routed back into the compressor
inlet. This limits the cooling capacity of the compressor.
Compressor Speed control
The volume flow of the refrigerant is changed by varying the rotating
speed of the compressor.
On-off control
The compressor is switched on if cooling is required, and switched off if
no cooling is required. This is the most simple, but also the crudest, way
of compressor capacity corvirol. It is mainly applied in small AC systems.
Cylinder unloading
During full load, all ine cylinders of a reciprocating compressor are in
operation. When the loac drops, one cylinder is taken out oí operation.
This procedure is continued as long as the load drops. When the load
increases again, the last cyiinder taken out of operation, is put back into
operation.
Muitiple compressor control
During full load, all the compressors are running. When the load crops,
one compressor is taken out of operation. When the load drops further,
another compressor is iaken out of operation. When the load increases
again, the last compressor iaken out of operation, is put back into
operation.
Condensers and cooling towers
Apparatus used in air-conditioning systems io reject heat include air-cooled
condensers, evaporative condensers and cooling towers.
Air-cooled condensers
Figure 5.40 shows a schermatic drawing of an air-cooled condenser. The
condenser consists of a heat exchanger, which rejects heat from the
refrigerant to the outside air, and a fan to improve the heat exchanging
process by means of forced convection. For the sake of completeness,
the condenser is shown as a part of the entire refrigeration process.
Fan
Heat exchanger
Outsideair
Expansion mechanism
Evaporator
Condenser
Compressor
Figure 5.40 Schematic layout of an air-cooled condenser
The advantages of air-cooled condensers are:
Niechanical simplicity
Low initial cost
Efficiency is independent of wet-bulb teinperature. This may be
desirable in geographical areas with high humidity.
Ideal for small systems
if used in geographical areas with low humidity, maintenance cost
is low
The disadvaniages of air-cooled condensers are:
For large systems, large heat exchangers may be required
If used in areas with high humidities, such as in coastal regions, life
span may be shortened due to iust
Evaporative condenser's
A schematic drawing of an evaporative condenser is shown in figure 5.41.
Evaporative conder: sers make use of water instead of air to condense
the refrigerant. Water is sprayed onto the condenser. The water
evaporates and extracts hear from the refrigerant gas, which condenses
and becomes a liquid. The water is pumped to the sprays from a sump at
the bottom of the condenser. The water which is lost due to evaporation,
is replaced by means of a make-up system.
Fan
Condenser
Air out
Water sprays
Pump
Air inMake-up Du
waterCompressor
Expansion
mechanismEvaporator
Figure 5.41 Schematic layout of an evaporative condenser
The advantage of an evaporative condenser is that it is smaller in size
ihan an air-cooled condenser, due to the fact that water is used instead
of air.
The disadvantages of evaporative condensers are: Condensing capacity is limited by the air wet bulb
temperature. In
geographical areas with high humidity, performance may suffer.
Water is sprayed onto a condenser coil at high temperature. This
can be a source of scaling, which reduces heat transfer. Water
treatment can be applied to limit scaling.
Water consumption.
Cooling towers
A schematic drawing of a cooling tower is shown in figure 5.42. A water
cooling coil is mounted in the cooling tower. Water pumped from ihe
sump is sprayed onto the coil and evaporates, thereby cooling the water
in the coit. The water in the coil is circulated through the condenser to
condense the refrigerant. As is the case with evaporative condensers,
the water which has evaporated, is replenished from the mains.
The acivantages of a cooling tower are:
Smaller in size than an air-cooled condenser.
The water in the coil is at a lower temperature than the refrigerani.
Scaling is therefore not as serious a problem as in the case of
evaporative condensers.
The disadvantages of a cooling tower are: Mechanical complexity due to the large number of
components
High initial and maintenance cost
Water consumption
Fan
Water
cooling
coil
Air out
Air in
Make-up ADH
water
Expansion
mechanism
Condenser
Evaporator
Sprays
Water
pump
Compressor
Figure 5.42 Schematic layout of a cooling tower
5.3.12 Heat pumps
The term "heat pump" is used to describe an AC system which has the ability to
make use oi jis cooling components to supply heating, and vice versa. This
reversible action is particularly ciesirable for cooling in summer and heating in
winter. li is both cost and energy efficieni, since no additional heating components
such as electrical heaters, are required. However, heating and cooling cannot be
supplied simultaneously, which may limit the capability of the system to control
humidity.
In cooling-only systems (see figure 5.24), the evaporator is placed in the room air
cuirreni, while the condenser is placed ouisice. The compressor inlet (suction side)
is connected to the evaporator, while the coinpressor outlet (discharge side) is
SUILDING SERVICES
connecteci to the condenser. In heat pump systems, the compressor suciion and
discharge connecting points car be changed around. The cooling system
evaporator becomes the heating system condenser, while the cooling system
concenser becomes the heating system evaporator. A flow valve situated between
the compressor and ihe heat exchargers, can be switched to select the desired
mode, i. e. cooling or heating. When the "cooling mode” is selected, the system
operates as indicated in figure 5.24. When the heating mode” is selected, the
valve connects the suction side of the compressor to the outside heat exchanger
and the discharge side to the heat exchanger in the room air current. Evaporator
heat is supplied by the environment, while condenser heai is rejected into the rooin
air current
5.4 LIFTS AND ESCALATORS
The main similarities and diíferences between lifts and escalators, from Stein and
Feynolds (1992), are: Lifts and escalators are used for vertical travel in buildings, that is, between
floors.
Lifts move up and down in a vertical plane, while the direction of motion of
escalators is sloped, like a moving staircase.
Lifts can transport passengers and a large variety of cargo, while escalators
are essentially used for passenger transport.
Lifts are considerably more space efficient than escalators. The space
consumption of a lift is only slightly bigger than its floor area, while escalators
can take up a significant part of the floor area of a building.
Lifts are indispensable for vertical travel in high rise buildings, while escalator
travel is limited to five floors at most.
Lift motion is interrupted at floors where passengers and cargo enter and exit,
while escalator motion is continuous.
Lift passengers must wait for the lift to arrive and doors to open before travel
can begin, while escalator passengers can be transported almost immediately.
Lifts are enclosed cabins, while escalators are open.
Due to their size, escalators are more visible than lifts.
Lifts musi be installed during the construction phase of the building, while
escalator installation may be possible at a later stage.
Lifts can be installed on the outside of buildings to provide passengers with
a good view of the surroundings. Escalators, on the other hand, can be used
to improve the appearance of buildings on the inside. In shopping centres, for
instance, escalators can be used to create an impression of spaciousness.
5.4.1 Lifts
The four most important building lift types are:
Passenger lifts
Cargo lifts
Hydraulic liſts
Special lifts: Panorama lifts
Chair lifts
Dumbwaiters
Passenger lifts
A schematic drawing of a passenger lift, indicating the most important parts,
is shown in Figure 5.43.
The most imporiant passenger lift parts are: vachine: The machine provides the power to move the
cabin up or
down.
Controller: The controller controls the speed of the machine.
Hoisi ropes: The hoist ropes connect the machine with the cabin and
lift or lower the cabin.
Counterwsight: The counterweight is attached to the motor by means
of a hoist cable. The counterweight balances the cabin in order to limit
machine power during motion.
Guide rails: The guide rails accurately guide the motion of the cabin
and the counterweight.
Governor: The governor limits the speed of the cabin in the interest of
safety.
Cabin (car): The cabin or car provides a safe, enclosed space for
passengers to travel in.
Cabin doors: The cabin doors close the cabin off during emotion and
make entry to and exit from the cabin possible when the cabin stops.
Roller guide: The roller guide keeps the cabin in contact with the guicie
rails and facilitate smooih motion of the cabin.
Oil buffer: The oil buffer stops the cabin in case of overtravel.
Hoist cables
Guide rails
Cabin door
Roller guide
Controller
Machine
Governor
Counterweight
Cabin (car)
Oil buffer
Figure 5.43 Schematic drawing of a passenger lift
Passenger lift service terminologios (Siein & Reynolds, 1992)
The definitions of the different passenger lifi service terminologies and
recommended values of each are as follows:
Interval
Interval is the average time between lift departures from the ground
floor landing. Suggested intervals can vary from as short as 25
seconds for city office buildings to as long as 120 seconds for low
income flats.
Average waiting time
Average waiting time is the average time spent by lift passengers
between arriving at the ground floor landing and getting into the lift.
Suggested average waiting time can vary from as short as 15 seconds
for city office buildings to as long as 26 seconds.
Registration time
Registraiion time is the waiting time at an upper or basement floor
after ordering a lift. Registration times can vary from 15 seconds
to 50 seconds, depending on the time of day.
Round trip time
Round trip time is the average time between depariure from the
ground floor landing, inaking all the required stops and arriving back
at the landing. Round trip time depends on the number of lifts and
the interval. The relationship between round trip time, interval and
number of lifts is given by ihe following equation:
S
RT
where / is the interval, RT is the found trip iime and N is the
number of liſts.
Travel time
Travel time is the average time spent by passengers from entering a
lift at the ground floor landing and leaving at an upper or basement
floor. A travel time of 1 ininute is highly ciesirable, while a travel time
of 2 minutes is on the limit of tolerance.
Handling capacity
Handling capacity is the number of passengers that can be
transported by a liſt system in a given period of time, usually 5
minutes. Suggested handling capacities vary from 5 for prestige
flats to 16 for single purpose office buildings.
Passanger lift propulsion systerne
Lift power is an important parameter in the design, selection and
specification of a suitable lift systein for a particular building. Lift power
will necessarily affect building power requirements, and it will therefore
be essential to limit lift power to acceptable levels. Lift power depends
on two factors, nainely lift mass and lift speed.
Recommended minimum lift speeds for given masses for a number of
building types, from Stein and Reynolds (1992), are shown in table
5.18. Lift power increases with both mass and speed, as shown
graphically in figure 5.44.
The following iwo traction machine iypes are used in lift propulsion
systems:
Gearless traction machines
Gearless traction machines are directly coupled to the hoist cable
pulley, and do not require gearboxes to transmit power from the
machine to the pulley. Gearless traction machines are used for
medium and high lift speeds, i. e. 2,5 m/s and above (Stein &
Reynolds, 1992).
Geared traction machines
Geared traction machines, on the other hand, make use of gears
to transmit power from the traction machine to the pulley. Geared
traction machines are used for cabin speeds of up to 2,25 m/s.
Table 5.18 Recommended lift speeds for given lift masses, travels and building types
Building type
Office buildingsSmall building
iviedium building
Large building
Hotels
Hospitals
Block of flats
Shops
Power
Car capacity
1 150
1 350
1 600
1 150
1 350
1 600
1 800
900
1 150
1 600
1 800
2 300
Increasing mass
Speed
Car travel
0-38
39 - 70
71 - 8586 - 115
Above 116
As above
0 - 18
19-30
31 - 38
39 - 53
54 - 75
Above 75
0 - 23
24 - 38
39 - 60
Above 60
0 - 30
31 - 45
46 - 60
Above 60
Minimuin car specu
1,75 - 2,00
2,50 - 3,003,50
4,00
5,00
As above
0,75
1,00 - 1,25
1,25 - 1,50
1,75 - 2,00
2,50 - 3,003,50
0,501,00
1,25 - 1,50
1,75 - 2,00
1,00
1,25 - 1,50
1,75 - 2,002,50
Figure 5.44 Lift motor power versus mass and speed
Lift cabin acceleration and deceleration are accomplished by controlling
the speed of the motor that drives the lift iraction machine. Speed control
can be accomplished in a number of ways, such as the following (Stein
& Reynolds, 1992):
Rheostatic control of a single-speed alternating current (AC) iraction
motor
Rheostatic control of a two-speed AC traction motor
Thyristor conirol of an asynchronous (squirrel cage) AC traction
motor
Thyristor control of a direct current (DC) traction inotor
ivotor-generator sei control of a DC traction motor, also known as
the Ward-Leonard or unit multi-voltage (UMV) system.
Variable voltage variable frequency (WWF) control of anasynchronous AC traction motor
The comparative characteristics of lift propulsion systems, from Stein
and Reynolds (1992), are summarised in table 5.19.
Table 5.19 Comparative characteristics of lift propulsion systems
Type
Geared AC
Geared DC
Gearless DC
Gearless AC
Rise
45
75
90
50
75
Unlimited
Unlimited
Speed
(m/s)
0,25-1
0,75-1,75
0,75-2,25
0,25-2,25
0,25-2,25
2-6
2-6
Control
Rheostat
Thyristor
WWF
UiV
Thyristor
UMV
Thyristor
WWF
initial
Cost
Medium
High
Medium
iiedium
Medium
Medium
Operating PerlormanceCost
Passenger lift emergency equipment
Lift emergency equipmeni inclucies ihe following:
Medium
Medium
High
Low
LOW
Poor
Fair
Excellent
Excellent
Very good
Excellent
Excellent
Excellent
Emergency brake
The brake is automatically activated wien lift acceleration exceeds
the inaximum safe value. The brake inay also be activated from
insicie the liſt in unforeseen circumstances.
Alarm
The alarm button can be sounded io alert the lift control room.
Intercom System
An intercom system provides communication between the liít and
the lift control room.
Ventilation fan
A roof-mounied fan, which provides ventilation during normal lift use,
also serves as a means to provide ventilation during energencies.
Cargo lifts
Cargo lifts have essentially the same system components as passenger lifts,
but are designed for hard service. The differences between passenger lifts
and cargo lifts are as follows (Stein & Reynolds, 1992): Various classes of loads may be carried, from
hanc-loaced cargo to
truck-loaded cargo, including the truck.
Speeds are generally between 0,25 m/s and 1,0 m/s.
Geared-type traction is used almost universally.
Cargo lift cabins are made if thick, heavy gauge steel with a multi-layer
wooden floor.
Guarded ceiling light fixtures are required.
The inside surfaces are usually equipped with high durability covers for
protection against hard and sharp objects, e. g. furniture, machines,
electric and electronic equipmeni.
Doors may open vertically to facilitate loading and unloading.
Door operaiion may be automatic or manual. Automatic door operation
can increase installation cost by as much as 10% to 25%.
Cargo lifts may, in some cases, be required to transpori passengers.
Hydraulic lifts
A hydraulic lift system consists of guicie rails, guice shoes, a cabin (car),
cabin coors, hydraulic cylinder, hydraulic plunger, buffer spring, hydraulic
pump, hydraulic pump motor and a hydraulic valving system.
A schematic drawing of a hydraulic lift is shown in figure 5.45.
Cabin
Guide shoe
Hydraulic
pump
with motor
Hydraulic valve
Guide rails
Cabin doors
Hydraulic cylinder
with plunger
Buffer spring
Figure 5.45 Schematic drawing of a hydraulic lift
Hydraulic lift operation is as follows: During upward travel, the pump raises
the hydraulic fluid pressure in the cylinder, thereby pushing the plunger,
which is attached to the lift floor, upwards. Lift speed is controlled by
hydraulic fluid flow, which is determined by pump power and lift mass. The
lower the lift mass, the higher the speed for the same power. During,
downward travel, the pump is switched off and the liſt is lowered by gravity.
Lift speed is controlled by valves, which limit the hydraulic fluid flow in the
cylinder. A buffer spring acis as the only safety mechanism in case of pump
andi valve failure.
Hydraulic lifts are mainly used for low cabin speed, low-rise, where absence
of the overhead machine room is clesirable and where the construction of
the plunger pit cioes not present difficulties.
The advantages of hydraulic lifts are:
Simplicity of the traction system
Simplicity of the control system
Simplicity of the safeiy devices
The disadvantages of hyciraulic lifts are:
Travel heights are restricted by cylinder and plunger lengtiis
Low speeds
Hydraulic system may require frequent maintenance
Construction of the plunger pit may be difficult
Special lift types
Speciai lift types include:
Panorama type lifis
Panorama type lifts are usually installed on the outside of buildings. The
cabin walls are transparent, with large glass areas, to provide passengers
with a good view of the surroundings. Panorama liſts may in some cases
also be instailed inside buildings to provide passengers with a view of
the building interior. This lift type is particularly appealing in spacious
shopping malls.
Chair lifts
Chair lifts are used for vertical transport of handicapped passengers. A
chair lift consists of a single chair which is propelled up and down stairs
by means of a worm gear and a rail attached to the stairs. The seat and
armrest can fold away for economical space utilisation when the chair
is not in use. Typical loads and speeds are 140 kg and 0,25 in/s
respectively.
Dumbwalters
Dumbwaiters are simple cargo lifts which transport small articles between
building levels. Dumbwaiter loading and unloading may be manual or
automatic. A dumbwaiter with an automatic loading facility is also known
as an ejection lift. Dumbwaiter applications include: A book lift in a library, where the book load may be
too heavy to
carry up and down stairs
Stock lifts in shopping centres
Medicine, food and linen lifts in hospitals
Food lifts in multilevel restauranis
5.4.2 Escalators
The main parts of and escalator are the moving steps, handrail, step and handrail
drive motor, truss structure, glass balustrade, metal balustrade, and the emergency
stop button.
A schematic drawing of an escalator, with the main parts, is shown in figure 5.46.
Moving steps
Lower level
Metal balustrade
Handrait
Truss structure
Glass balustrade
Figure 5.46 Schematic drawing of an escalator
Emergency
stop button
Upper level
Step and handrail
drive motor
Two escalator configuracions, or layouts, used in buildings are the parallel and
criss-cross configurations.
Parallel configuration
The parallel configuration is shown in figure 5.47. All the escalators travelling
up are on the same side and all the escalators travelling down are on the
opposite side.
Griss-cross configuration
The criss-cross configuration is shown in figure 5.48. The escalators travelling
up follow each oiher on opposite sicies. Likewise, the escalators travelling
down follow each other on opposite sides.
The advantages and disadvantages of the parallel and criss-cross layouts
are as follows (ivicGuinness et al., 1964): The criss-cross layout is structurally stronger than the parallel
layout.
The criss-cross layout consumes less floor space than the parallel layout.
The criss-cross layout is cheaper than the parallei layout.
The parallel layout is aesthetically more pleasing than the criss-cross
layout.
A
View A-A
Figure 5.47 Escalator parallel configuration
B
B
View B-B
Figure 5.48 Escalator criss-cross configuration
Escalator size is normally expressed in terms of the stair tread width. (In the
past size was expressed in terms of width between balustrades at hip level.)
Treads are normally 400 mm long and 200 mm high. The following stair sizes
are standard (Stein & Reynolds, 1992):600 mm stair tread width (800 mm width between balustracies at
hip level)
800 mm stair tread width (1 000 mm width between balustrades at hip
level)
1 000 inm stair ireaci width (1 200 mm width between balustrades at hip
level)
Escalator passenger capacities for the different sizes, from Stein and Reynolds
(1992), are given in table 5.20.
Table 5.20 Escalator passenger capacity
Tread width(mm)
600
800
1 000
Speed
(m/s)
0,5
0,5
0,5
Passengers per hour
axinyum Design Observed
5 200
7 300
9 000
4 000
5 300
6 750
2 300
2 900
4 500
The maximum passenger capacity refers io the theorežical maximum capacity.
The design capacity is valid for heavy loading, while the observed capacity
refers to the average long-period loading. Note that the 0,5 m/s speed is
standard for all sizes. This is less than the inaximum safe allowable speed
of 0,625 m/s prescribed by the ANSI/ASiviE 17.1 safety code.
Escalator moior power depends on size and height. ivotor power, from
Stein and Reynolds (1992), is given in table 5.2i.
Table 5.21 Escalator motor power
Escalator tread size(mm)
800
800
800
1 200
1 200
1 200
Maximum risc(m)
4,25
6,75
9,00
3,00
4,50
6,00
Motor size
3,75
5,50
7,50
3,75
7,50
11,25
Escalator safety requirements, from ivicGuinness et al. (1964), are as follows: Steps and handrails must
move at the same speed
Steps must be designed to prevent slipping of passengers
Steps must level at lower and upper landings to prevent tripping of
passengers
Balustrades must be smooth on the inside to prevent gripping of
passenger clothing
In case of electrical power failure, the steps and handrail must come to
a smooth stop
In case of overspeed or underspeed, a governor inust siop the escalator
and prevent reversal of motion
Landings must be properly illuminated
An emergency stop button must be provided
5.5 MECHANICAL SYSTEMS
5.5.1 Pneumatic tube transport systems(Building Services GBD 222 class notes)
A schematic layout of a number of simple pneumatic iube transport systems is
shown in figure 5.49.
Single line reversing: Send, receive
Single fine reversing
with central station: Send, receive (U!
Dual line:
Station
wiulti-tube central station:
Fan o
Central station
Ofan
Fan
Fan o
Send
Send, receive
Send, receive
Receive
Figure 5.49 Schematic layout of typical pneumatic tube transportsystems
The principle of operation of a pneumatic tube transport system is as follows:
Capsules are used to transport articles in buildings and factories by means of air
flow in tubes. A capsule is placed in the tube at one station, from where the air
flow moves the capsule to its destination. A fan is used to force the air througir the
tube. The fan can either be of the suction (vacuum) type, or the blower (positive
pressure) type. It is situated close to the system, usually at one end of the tube.
Tube materials are metal or plastic (PVC), depending on the application. Pneumatic
tube system layouts can vary in complexity, from the single line reversing layout to
a multi-tube central station layout. The different layouts are shown in figure 5.49.
Pneumatic iube applications are as follows:
Light duty application
Low temperature
Small size: Tube internal diameters from 55 mm to 125 mm
Capsule diameters from 32 mm to 90 mmCapsule lengths from 215 mm to 350 mm
Low mass:50 gram to 2 kg
Low capsule speed: 6 m/s
Tube inaierial: Plastic
Heavy duty industrial application
High temperature: Up to 1 000 °C
Large size: Capsule diameters of up to 200 mmCapsule lengths of up io 500 mm
high ass: Up to 10 kg
High capsule speed: Up to 17 m/s
Tube material: Metal
5.5.2 Smoke detection and fire prevention
‫܀‬
The stages of a fire
iviost fires pass through four stages (Stein & Reynolds, 1992). These stages
and their respective detection ineihods are described in short below:
Incipient stage
During this stage no smoke, visible fianie or appreciable heat is present.
An invisible particulate matter is given ofi, the size of which is 0,01 io
1 um. This stage is besi deiecied by ionisation-type detectors, which
contain a small amount of radioactive material that serves to ionise the
air between two charged surfaces, causing a current to flow.
Smouldering stage
During this stage, ilame or appreciable heat is still not present. Large
particles, with a size of up to 10 um, are visible as smoke. This stage
is besi detected by photometric detectors, which operates as follows: A
bear of light is directed onto a photosensor and a no-smoke circuit
condition is established. The presence of smoke will partially obscure
the beam, changing the current flow in the photocell and setting off an
alarin.
Flame stage
Heat is still not present, but follows almost immediately. The actual fire
now exists. This stage is best detected by ultraviolet (UV) radiation
detectors. These operate by detecting the UV radiation produced by
flames, which is typically in the 170-290 lm range. Organic material
iypically produces strong radiation in this range.
Heat stage
During this stage heat is uncontrolled and air expands rapidly. The fire
is burning openly and producing great heat, incandescent air and smoke.
This is the most dangerous stage of the fire, and is best detected by heat
detectors of which two types are used:
Spot heat detectors
Two types of spot heat detectors are used, namely fixed temperature
detectors, which come into operation when a fixed temperature in
the range of 57 °C to 85 °C is reached, and rate-of-rise detectors,
which detect the rate of the rise in ambient temperature.
Linear heat detectors
The iwo types of linear leat detectors that are used are ihermoplastic
insulation and linear thermistor. Thermoplastic insulation consists
of iwo wires, separated by a plastic insulation layer. When the
insulation melts due to heat exposure, the wires come into contact,
change the current flow in ihe circuit and sound an alarm. Linear
thermistor is a device whose electrical resistance changes with
temperaiure. The resistance is imonitored at a control panel. The
cleteciion range can be sei anywhere from 21 °C to 650 °C.
Smoke management
A number of smoke inanagement options exist, such as: Smoke confinemeni, where the smoke is
passively confined to the fire
area itself.
Smoke dilution, wiere 100% of outside air is provided by the AC system
to make conditions bearable for occupants during building evacuation.
Exhaust sysiemwhich only operate in a fire. These systems employ both
air speed and air pressure to help control smoke.
Fire suppression
Fire suppression can be done with water and other fire-suppression media.
Using water for fire suppression
Fire suppression is mostly done with water. Water is supplied by means
of hoses and sprinkler systems. Hoses are essential in high multilevel
buildings where upper floors cannot be reached by fire-fighting equipment.
Sprinkler systems are used in warehouses, stores, theatres, offices and
homes. It consists of a horizontal patter of pipes running near the
ceiling. These pipes are provided with sprinkler heads which, when
subjected to high temperatures, open automatically and emit fine water
sprays. Water discharge takes place at temperatures of at least 14 °C
above the maximum expected ceiling temperature. Sprinkler spacing
depends on the hazard. For low hazards, spacing may be as high as
18,6 m on main lines, while for high hazards, spacing may be as little
as 3 m on branch pipes.
The following four sprinkler system types are used in buildings: Wot-pipe: Water is always under
pressure in all pipes and mains.
Dry-pipe: Pipes are filled with compressed air until the opening of
one sprinkler head allows water flow.
Pre-action: Pre-action systems are similar in operation to dry-pipe
systems, with the exception that water flow into the pipe is allowed
before any sprirkler head has opened. This system requires an
extremely early alarm.
Deluge: All the sprinkler heads spray at once.
Using water for fire extinguishing purposes has the following
advantages (Stein and Reynolds, 1992):
Water is relatively cheap
Water smothers
Water emulsifies
Water dilutes smoke, and poisonous and toxic gases
Water cools. When water evaporates, it removes 2 256 kJ of heat
per kg at atmospheric pressure, and expands 1 700 times, therebydisplacing oxygen required to sustain
fires
The disadvantages of using water for fire suppression are: It damages building content
It conducts electricity
Flammable oils float on water, without being extinguished
Water vaporises as steam, harming firemen
Other fire suppression media
Other fire suppression media are:
Intumescent materials
Intumescent materials expand rapidly after being exposed to fire.
This process creates air pockets that insulate a surface from the
fire, or swell a material until it blocks openings through which fire or
smoke could have passed. Paints, caulks and putties are available.
Carbon dioxide
Carbon dioxide (CO2) is found in poriable fire extinguishers. CO2
smothers a fire by displacing oxygen, and is suitable for electric
fires. However, CO, can only be used in tightly confined spaces
free of people and animals, it presents a danger to firemen and it
may allow smouldering fires to re-ignite.
Foams
Foams are masses of gas-filled bubbles (lighter ihan water and
flairmable liquids), and are therefore especially effective in
extinguishing oil fires. However, lighiweight foams can be diverted
away from a fire by air turbulence.
Halogenated agents
Halogenated agents are also known as halons. The most familiar
halon is Halon 1301, the molecule oí which consists of one carbon
atom, three fluorine atoms, io chlorine ators and one bromine atın.
The fire extinguishing mechanism of Halons differs from those of
other media. Whereas water and CO2 inhibit fires physically,
Halons inhibit fires chemically. Halons are particularly suitable for
extinguishing fires in rooms where sensitive or expensive equipment
is used, for instance in computer rooms, libraries, museums,
telephone exchanges and kitchens. Halons do not damage
equipment and are non-toxic. Halons are light in weight and
therefore consume less space than other suppressants. Halons
are found in portable fire extinguishers.
The disadvantages of halons are: Halons are inore expensive than waier and CO2
Halons are not suitable for metal fires or gunpowder
Halon is heavier than air and tends to stratify
In hign concentrations, halons cause dizziness and impaired
co-ordination
5.5.3 Central vacuum cleaning systems(Building Services BGD 222 class notes)
The principie of operation of a central vacuum cleaning (CVC) system is as
follows: Each room in the building is supplied with an air suction point, which is
connected to a remote vacuum plant by means of a built-in piping systein. The
plani consists of an extract ian, powered by an electric motor, and a combined
filter/dirt collecting unit. The plant may be situated in any convenient place in
the building, such as in the basement, in the parking area, or in a specially built
room. The fan runs continually, thereby providing a permanent vacuum at the
suction point. Flexible hoses, similar to those supplied with portable, domestic
vacuum cleaners, are provided with the system. Dust and dirt are collected by
the hoses and transported to the filter/collecting unit by the air flow in the piping
system.
A schematic layout of a typical CVC system is shown in figure 5.50.
Piping system
CVC
plant
room
Suction fan
Flexible hose
Multilevel
building
Basement
Filter/dirt collecting unit
Figure 5.50 Schematic layout of a typical central vacuum cleaningsystem
Advantages of CVC sysiemsit is a powerful method of cleaning buildings. The system can be
designed to give ihe correci air flow required in each room.
CVC equipment is easy to handle. The only mobile equipment are the
suction hose and nozzle, which are light and small. The cleaning task
can iherefore be done quickly and efficiently and with relatively low strain
on cleaners and operators.
Due to the low mass of the mobile CVC equipment, damage to ihe
building, furniture, carpets and other floor coverings is low.
Dusi control is improved. CVC systems have remote filter and collecting
units, ihereby minimising resettling of dirt on raierial and furniture.
CVC systems require minimum maintenance. The system has only two
moving paris, i. e. a fan and a fan motor, which are of robust design and
only require periodic lubrication and belt adjustment.
Noise levels of CVC sysiems are considerably lower ihan those of local
vacuum cleaning systems. The only noise source in the rooin is the air
flow ihrough the suction nozzle, which is negligible in comparison with
fan motor noise.
CVC sysiems require no electrical cables in the cleaning space. This
improves system reliability and reduces the risk of short circuits and
electrical fires.
Labour costs are lower than in the case of local vacuum cleaning
systems. The higher efficiency of CVC equipment makes it possible to
reduce cleaning time consicierably.
CVC systems can operate in a large variety of building types, such as
offices, shops, factories, warehouses, hospitals, laboratories, process
plants and foundries.
CVC systems give a high return on investment (ROI), made possible by
reduced maintenance and labour costs.
Disadvantages of GVC systemsAlthough the running cost of CVC systems is relatively low in comparison
with local vacuum cleaning systems, the installation cost is higher.
CVC systems require additional space for the piping system and plant
room.
A CVC system must be installed during the construction stage of a
building. Installation at a later stage would necessitate alteration of the
building and building structure. The cost of these alterations could offsei
the reduced running cost to such an extent that the system may no longer
be desirable.
5.5.4 Waste removal (Building Services GBD 222 class notes)
Waste removal is mainly done by local authorities. The tariffs of waste removal
are calculated according to waste volume. The lower the volume, the lower the
cosi. It is therefore clear that cost can be saved by reducing waste volume. This
can for instance be done by separating and compacting different waste types.
The differeni waste types and the handling of each are discussed as follows:
Office waste
Paper is ihe largest contributor. It must also be borne in mind that kitchens
may be responsible for food left-leftovers. Office waste is handled in the
following ways: Cleaning services remove waste with irolleys.
Drop chutes (typically 400 mm in diameier) can be used in multilevel
buildings to transport dry waste from upper levels to the ground level or
basement, from where cleaning services or local authorities can remove
the waste.
Waste paper is recycled.
Waste can be compacted.
Industrial waste
Industrial waste inainly consists of abattoir waste and chemical wasie, suci
as nuclear waste. Industrial waste is handled as follows:
Abattoir waste such as blood, bones and skins can be recovered. In
order to prevent the spreading of pests and diseases, precautions musi
be taken against theft of waste.
Chemical waste is sealed in large steel drums and buried.
Nuclear waste is sealed in large steel drums, which are cast in a thick
layer of concrete and buried or dropped in the ocean.
Kitchon waste
Kitchen waste mainly consists of fai, soap and vegetables. Kitchen waste is
handled as follows:
Vegetable waste is sold to pig farmers.
Shredders can be connected to the sewage system to shred waste in
order to prevent blockages.
Leftovers are removed by local authorities and discarded at a dumping
site.
Hospital waste
Hospital waste can be divided into hospital waste and kitchen waste. Kitchen
waste is treated as described above. Hospital waste is handled as follows: Theatre waste, syringes and
bandages are burnt.
General waste is either burnt or removed by locai authorities.
Precautions must be taken against theft to prevent spreading ofdiseases.
A reſuse room may be a valuable aid in the general organisation of wasie handling,
and may facilitate security and the maintenance of health and hygienic standards.
A schematic layout of a typical refuse room is shown in figure 5.51.
Burglar-proofed
vents
11
11
i
Тар,
Drain point
Ceiling mounted lights
Figure 5.51 Schematic layout of a typical refuse room
The factors involved in the planning of a refuse room are:
‫܀‬
Electric power
point for
compactor
Industrial
quality tiles
Lockable
doors
Ramp
Accessibility
Ramps which lead to the refuse room inust have a slope of less than 1:7.
Heavy vehicles must be able to turn inside ihe room, as well as enter and
leave the room with relative ease.
Draining
Liquid waste will be handled inside the refuse room. In order to provide
sufficient efflux of liquids, the room must be properly drained and its iloor
must stope downwards to the draining point.
Interior surfaces
Bins and craies are thrown around and may cause damage to interior
surfaces. Walls and floors must be protecied by hard and durable coverings
or coatings, e. g. inciustrial quality tiles and paints.
Water reticulation
Atap must be provided to wash interior suriaces.
Ventilation
Odours may build up in a refuse room. Veniilation is therefore of prime
importance. Two types of ventilation can be applied, i. e. natural ventilation
BUILDING PPACTICE - VOLUME 1
and forced ventilation. Natural ventilation is accomplished by the provision
of openings in walls and doors. This system is inore effective if the openings
are installed in opposite walls, thereby providing cross-ventilation. Forced
ventilation is brought aboui by a roof-mounted extract fan, in combination
with a wall opening. The latter is provided to prevent vacuum build-up in
the room.
Sscurity
Thefi of refuse may occur. To preveni this, the room must be supplied with
lockable doors and burglar-proofing.
Illumination
Ample lighting must be provided.
QUESTIONS FOR SELF-EVALUATION
1.
2.
3.
4.
5.
S.
7.
8.
9.
Name three types of pipe materials that are commonly used to
distribute water in buildings and explain in which circumstances
you would use the different pipe materials.
Name ihree iypes of electric storage heaters.
Discuss the use of electric water heaters.
Whai are the main requirements of a drainage sysiem?
Discuss safety valves used in a water reticulation system.
Discuss the efficiency of gas-fuelledi waler heaters in relation to
electric heaters.
Discuss the water supply problems, regarding pressure, which are
encountered in high-rise buildings and possible solutions lo inese
problems.
(6)
(3)
(15)
(5
)
(5)
(8)
Demonstrate ihe general requirements for underground drains by
means of a sketch.(10)
Name and sketch three pipe systems which can be used in
buildings to regulate crainage.
(15)
(continued...
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21,
22.
Discuss access to drainage pipes.
What is Ohm's Law?
Define: ohmampere
volt
What factors determine the electrical conducting ability of a
substance?
A2 22 resisiance and a 42 resistance are connected in serie and
ihen connected in parallel with a 6 12 resistance. This combination
is connected in serie with a 3.2 resistance. What is the tota!
resistance of the network of resistances?
A battery with a terminal voltage of 9 V supplies a current of
12,5 mA to an electronic circuit. How much power is consumed
by the circuit?
An electrical circuit with a resistance of 2,5 12 consumes 100 KW.
Calculate the supply voltage.
(3)
(3)
(9)
(4)
(8)
(8)
(8)
A three ohm and a 6 $2 resistance are connected in parallel and then
connected in serie to a 4 12 resistance. An emf oi 24 V is applied
over the circuit. Calculate the following:
(a) the total resistance of the circuit.
(b) the total current that flows in the circuit.
(c) the potential difference over the 3 ohm resistance.
(c) the current that flows through the 3 ohm resistance.
What are the motives which individuals or groups may have to
penetrate a building? Discuss briefly.
What are the general requiremenis for a security system?
Which general factors will you consider when iimplemeniing a
security system?
(12)
(14)
(5)
(12)
Which items will you consider when ciesigning a security sysie. n? (17)
What are the objectives of entrance control systems?
(4)
Icontinued...
23.
24.
25.
26.
27.
28.
29.
30.
31.
32.
33.
34.
35.
Name 5 types of entry control cards.
What are the characteristics (volume/nour, maintenance and cost)
of the different types of entry control mechanisms?
Name 10 iypes of sensors for exterior use.
Name 6 iypes of sensors for inierior use.
What are the bases of deteciion of the various types of fire
detectors?
Name 10 types of systeins that can be controlled from the central
computer panel.
Name the purposes of air-conditioning and give an example of
each.
Define the following air-conditioning terms:
(a) Dry-buib temperature
(b) Wet-bulb temperatureRelative humidity
(d) Specific humidity
(e). Specific volume
(6) Enthalpy
Name tire comfort criieria of air-conditioning systems.
Name 4 sources of latent heat and six sources of sensible heat
in buildings.
What are the advantages and disadvantages of central and local
air-conditioning systems?
Naine the reasons for fresh-air supply to buildings.
Define the following geometric and performance criteria of air
inlets and outlets:
(a) Aspeci ratio
(b) Induccion ratioThrow
(d) Drop
(e) Air change
(5)
(5)
(5)
(3)
(5)
(5)
(12)
(2)
(2)
(5)
(10)
(12)
(3)
(2)
(2)
(2)
/continued...
36.
37.
38.
39.
40.
41.
42.
Name ihe componenis of the refrigeration cycle and give the
purpose of each.
How can the refrigeration cycle be applied to bring about cooling
in suminer and heating in winter?
(8)
(8)
Name 10 similarities and differences between lifts and escalators. (10)
Name the purpose of all the parts of a passenger lift.
What are the differences between passenger lifts and cargo lifts?
Name the advantages and disadvantages of water as a fire
suppressant.
What are the factors involved in the planning of a refuse room?
REFERENCES
(10)
(9)
(8)
330
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Basson, J. A. 1982. "Die implikasies van verhoogde energiekoste vir geboue". Die Boubestuurder
1982:12-15.
Building Services GBD 222 class notes, University of Pretoria.
Burberry, P. 1970. Environment and Services. London: BT Batsford Ltd.
Burberry, P. 1975. Environmeni and Services. Batsforci, London: Ivitchell'sBuilding Construction.
Burberry, P. 1983. Practical Thermal Design in Buildings. Batsford, London: viitchell's Building
Construction.
Chadderion, D. V. 1991. Building Services Engineering. London: E & Fi Spon.
Chudley, R. 1987. Construction Technology. Volumes 2 & 4. Harlow: LongmansScientific & Technical.
Clark. B. H. 1983. Sanitary Plumbing Services in South Africa. Cape Town: Juta.
Cloete, C. E. & du Plooy, J. 1995. Security and its legal implications. CertificateCourse in Shopping Centre
ivianagement, iviarch 1995. Module presented at
SAPOA/University of Pretoria.
Coker, A. J. & Turner, W. 1992. Electric Wiring: Domestic. 10th edition. Oxford: Butterworth-Heinemann.
Colvin, T. S. 1989. Electrical wiring: student workbook. 4th edition. Athens: American Association for
Occasional Instructional Material.
Coren, S. & Ward, L. iv. 1989. Sensation and Perception, 3rd edition. Fort Worth: Harcourt Brace
Jovanovich College.
Daly, B. B. 1978. Woods Practical Guide to Fan Engineering. 3rd edition. Essex Telegraph Press.
Denny, M. G. 1985. Computerising energy management systems. Paperpresented at The 1985 Project
ivianagement Convention. P-E Corporate
Services,
Donnelly, E. L. 1980. Electrical Installation. Theory and Practice. 3rd edition. London: Harrap.
Florence, N. 1989. “Light Exercise. How to select luminaires for today's offices". Skylines. Nov/Dec
1989:21-27.
Grandjean, E. 1988. Fitting the Task to the Man. 4th edition. London: Taylor &Francis.
Fall, F. 1982. Electrical Services in Buildings for Architects, Builders andSurveyors. London: Construction
Press.
Hamilton, V. R. 1985. Nuwe Diploma Elektriese Ingenieurswese. Durban: Butterworth.
Helms, R. N. 1980. Illumination Engineering for Energy Efficient LuminousEnvironments. Englewood
Cliffs, NJ: Prentice Hall.
Holman, J. P. 1976. Heat Transfer. 4th edition. MicGraw-Hill Kogakusha.
Hughes, G. J. (ed.) 1984. Electricity and Buildings. London: Peter PeregrinusLtd. Chapter 4.9.
Hughes, S. D. 1988a. Electrical Systems in Buildings. New York: Delmar. Chapters 3-5.
Hughes, S. D. 1988b. Electrical Sysiems in Buildings. New York: Delmar. July 1984:57-60.
Jones, W. P. 1982. Air Conditioning Engineering. 2nd edition. Arnold.
Knight, J. & Jones, P. 1995. Newnes Building Services Pocket Book. Butterworth-Heinemann.
Langley, B. C. 1985. Control Systems for Air-conditioning and Refrigeration. Prentice Hall.
Lap, A. 1982. Electrical distribution in high-rise building. Planning and BuildingDevelopments, Sept/Oci
1982. Reprinted as R/Bou 987, NBNI, Pretoria:
CSIR. 3 pp.
Lap, A. 1983. iviisconceptions about the safety of wiring systems. MunicipalEngineer, 14(2). Reprinted as
R/Bou 1084, Pretoria: CSIR.
Lee, D. N. 1985. Energy saving – the lighting factor. Paper delivered at The1985 Project ivianagement
Convention. P-E Corporate Services. 17 pp.
Levermore, G. J. 1992. Building energy management systems. Chapman &Hall.
Lovins, A. B. & Browning, W. D. 1992. "Negawatts for Buildings. The whys andhows of electric
efficiency". Urban Land, July 1992:26-29.
iviartin, P. L. & Oughion, D. R. 1989. Faber & Kell's Heating and Air-conditioningof Buildings. 7th edition.
Butterworth.
viason, A. lvi. 1978. “Energy management in high-rise buildings". In Unisa,1978:105-116.
MicGuinness, W. J., Stein, B., Gay, C. ivi. & Fawcett, C. de V. 1964. Mechanicaland Electrical Equipment
for Buildings. 4th edition. New York: John Wiley.
ivicLean, G. 1984. “Are you taking your lighting seriously?" Supplement toPBD and MIE.
iviciviullen, R. 1983. Environmental Science in Building. Londor: iviaciviillan. Chapter 11.
iviorris, N. ivi. 1985. iviastering Electrical Engineering. 2nd edition. London: Macivillan,
iviullins, H. J. 1985. "Reducing and maintaining energy consumption". InCushman, R. F. & Rodin, N. I.
1985. Property ivanagement Handbook. A
Practical Guide to Real Estate Management. New York: Wiley. Chapter 10.
Oelofse, A. J. 1985. Optimisation of electrical and water tariffs. Paper presentedai The 1985 Project
ivianagement Convention. P-E Corporate Services. 17 pp.
Oliver, E. & Wilson, J. 1988. Practical Security in Commerce and Industry.5th edition. Brookfield,
Vermont: Gower.
Olley, A. H. 1978a. "Energy conservation in buildings: An architectural approach". In Unisa, 1978:45-63.
Olley, A. H. 1978b. "Retrofitting: Architectural redesign for energyconservation". la Unisa, 1978:55-77.
Page-Shipp, R. J. 1978. “General energy conservaiion in buildings: options forSouth Africa". In Unisa,
1978:1-19.
Poole, C. D. 1987. Electrical Distribution in Buildings. Oxford: BSP ProfessionalBooks.
Porges, F. 1989. The Design of Electrical Services for Buildings. 3rd edition. London: E & FN Spoil.
Pritchard, D. C. 1985. Lighting. 3rd edition. London: Longman.
Raissen, ivi. 1990. "Low voltage lighting". Planning 103:93.
Raphael, F. & Neidle, ivi. 1974. Electrical Wiring of Buildings. London: Pitman. Chapters 1-17.
Reid, E. 1984. Understanding Buildings. A multidisciplinary approach. London: Construction Press: 128135.
SABS 0114-1973. Code of Practice for Interior Lighting. Part I: Artificiallighting. 80 pp.
SABS 0'142-1993. Code of Practice for the Wiring of Premises. Pretoria: South African Bureau of
Siandards.
Shuttleworth, R. 1983. iiechanical and Electrical Systems for Construction. New York: McGraw-Hill.
Sitrin, T. 1989. "Visible diíference". Skylines, Nov/Dec 1989:16-17.
Sinith, C. B. 1981. Energy Management Principles. New York: Pergaimon.
Sorcar, P. C. 1982. Energy Saving Lighting Systems. New York: Van NostrandReinhold.
Spoormaker, H. & Puiten, P. 1989. "Heat, ventilation and air conditioningaspects of 5 Simmonds Street,
Johannesburg". Planning 101:27-37.
Spoormaker, H. J. 1978a. “Design of air-conditioned buildings and the influenceof rising building costs".
In Unisa, 1978:159-189.
Spoormaker, H. J. 1978b. “Retrofitting existing buildings and their systems”. InUnisa, 1978:213-225.
Stein, B. & Reynolds, J. S. 1992. iviechanical & Electrical Equipment for Buildings.8th edition. New York:
John Wiley.
Steward, W. E. & Stubbs, T. A. 1995. Modern Wiring Practice. Design andInstallation. i2th edition.
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Stoecker, W. F. & Jones, J. W. 1982. Refrigeration & Air-conditioning. 2nd ediiion. McGraw-Hil,
Kogakusha.
Stoecker, W. F. 1980. Design of Thermal Systems, 2nd edition. WicGraw-HillKogakusha.
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Unisa,
Van Aarle, G. 1985. Retrofitting existing air-conditioning systems to optimiseenergy consumption. Paper
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NOTES
CONTENTS
LEARNING OBJECTIVES
9.1
9.2
9.3
9.3.1
9.3.2
9.3.3
9.3.4
9.3.5
9.3.6
9.3.7
9.3.8
9.3.9
9.3.10
9.3.11
9.3.12
9.3.13
9.3.14
9.3.15
INTRODUCTION
DEFINING FAILURE AND MAINTENANCE
MAINTENANCE PROBLEMS AND SOLUTIONS
General
Soil types
Foundations
Wall cladding
Face brickwork
Structural steelwork and other metals
Timberwork, joinery and shopfitting
Solid floor coverings
Plasterwork
Paintwork
Plumbing and drainage
Flat roofs: concrete slabs
Plastics
Flood damage
Dampness and condensation
QUESTIONS FOR SELF-EVALUATION
REFERENCES
CO
PAGE
78
78
79
81
81
84
85
85
86
86
87
88
88
92
93
94
95
96
96
98
98
LEARNING OBJECTIVES
The objectives with this module are to outline the general principles underlying
building maintenance and to highlight some specific problem areas and their
solution.
After completion of this module the student should be able to:
‫܀‬
identify typical maintenance problems in buildings
use a sound practical approach in the execution of building maintenance
9.1 INTRODUCTION
A distinction has to be drawn between maintenance and building failure. All
buildings require maintenance, which primarily entails keeping a building in a
continuous state of repair, suitable for the intended use. Failure in turn refers to
a situation where an element, or even a building as a whole, deteriorates to such
an extent that premature maintenance is required to ensure that the building is
suitable for its intended use.
Building failures and high maintenance cost are mainly caused by poor design
and/or workmanship and to a small degree by faulty materials. In essence it can
be stated that high maintenance costs are mainly created on the drawing board
and/or by a lack of skill on site. To thus ensure quality and low maintenance it is
obvious that the aspects which need to be concentrated on are design and
workmanship. Buildings do however age, with resulting expected maintenance,
but this is not regarded as failure. Failure refers to situations where premature
maintenance is required.
Failure may also be caused by natural phenomena such as storms, earthquakes,
high winds and floods, or by abuse and general negligence to maintain property.
The end result of failure and of aging buildings is maintenance, the aspect which
will mainly be dealt with in this chapter.
When failure symptoms appear it is advisable to consult with experts. Failure in
buildings can lead to litigation, which should preferably be avoided in favour of
negotiation or arbitration. In the case of serious failures, which in practice entail
that the owner is the suffering party, it is obvious that he will endeavour to
minimise his costs by establishing if another party could be held accountable for
the failure. Insurance companies are also a natural possibility for the unethical
loading of claims.
A positive approach to long term maintenance is to firstly ensure that design and
site workmanship meet the owner's criteria regarding quality. In practice, total
quality management starts when the first line for the project is drawn. With that
having been adequately addressed, maintenance as a fact of life, should be
managed in a proper fashion. A lack of maintenance has cumulative results,
increasing the speed of deterioration and costs. The “cheapest" maintenance
remains “maintenance” which was never required because it was prevented from
occurring in the first place.
9.2 DEFINING FAILURE AND MAINTENANCE
To draw a clear distinction between "failure" and "maintenance" the following
definitions demarcate the sense in which it will be used in this chapter:
Failure of elements of, or a building as a whole, occurs when a situation arises
where the intended use of the building or sections thereof is hampered or become
unusable as a result of rapid deterioration requiring premature maintenance.
Seely (1987:1) defines maintenance as: “The combination of all technical and
associated administrative actions intended to retain an item in, or restore it to, a
state in which it can perform its required function".
Maintenance being a major element determining the quality of buildings, can be
defined by type or as per figure 9.1 (adapted from Seely (1987:2)).
Planned
maintenance
Preventive
maintenance
Scheduled
maintenance
Maintenance
Conditionedbase
maintenance
Figure 9.1 Types of maintenance
Unplanned
maintenance
Corrective
maintenance
Emergency
maintenance
D
Seely (1987:2-3) defines the types as follows:
Planned maintenance: "The maintenance organised and carried out with
forethought, control and the use of records to a predetermined plan”.
Unplanned maintenance: "The maintenance carried out to no predetermined
plan".
Preventive maintenance: "The maintenance carried out at predetermined intervals
or corresponding to prescribed criteria and intended to reduce the probability of
failure or the performance degradation of an item".
Corrective maintenance: “The maintenance carried out after failure has occurred
and intended to restore an item to a state in which it can perform its required
function".
Emergency maintenance: “The maintenance which is necessary to put in hand
immediately to avoid serious consequences."
Scheduled maintenance: "The preventive maintenance carried out to a
predetermined interval of time, number of operations, mileage, etc.".
Condition-based maintenance: “The preventive maintenance initiated as a result
of knowledge of the condition of an item from routine or continuous monitoring”.
Another approach to maintenance classification has been adopted by Speight
(as noted by Seely), who subdivided maintenance into three broad categories:
Major repair or restoration such as re-roofing or rebuilding defective walls and
often incorporating an element of improvement. (This item includes failure).
Periodic maintenance a typical example being annual contracts for decorations
and the like.
Routine or day-to-day maintenance which is largely of the preventive type, such as
checking rainwater gutters and servicing mechanical and electrical installations.
The types of maintenance as depicted above fall within the sphere of the present
day "Facilities Management", the latter being a totally encompassing approach
towards managing and maintaining a building complex. Sophisticated computer
programmes are available to deal with all aspects of property ownership,
including maintenance. The purpose with this chapter is not to address facilities
management, but only to isolate maintenance of structures and finishes from the
whole.
The standard of maintenance directly effects the quality of the built environment
and thus the quality of life in buildings. It therefore requires a conscious decision
to be taken by a building owner as to the "level" of maintenance required. In
South Africa the mainter ce standards of public buildings, particularly health
care facilities, have deteriorated to alarming levels. Only a major effort will save
these assets. It could possibly be disposed of on leaseback (or by other means)
to place the maintenance responsibility in the hands of the private sector. Neglect
is however also gaining ground rapidly in the private sector, which is experiencing
continuing growth in vacancy levels in city centre properties. Vacant properties
on which landlords loose money continuously are seldom maintained adequately,
leading to accelerated decline and as is the case in South Africa presently, inner
city decay. At this stage it is difficult to predict where the turning point in the
decline of public and inner city buildings will be. Meanwhile the maintenance
backlog is building up. Typically a building's economic life expectancy is 60 years,
but depending on the quality of the building, it could be substantially more. The
building's economic life is primarily determined by the income generated by it,
the cost to maintain it, or by outside factors such as the possible more profitable
use of the site, or changes in social and/or physical conditions which make the
building unsuitable for its originally intended use.
9.3 MAINTENANCE PROBLEMS AND SOLUTIONS
A variety of problems that may be expected will be described in this section,
listing possible solutions very briefly. The number of maintenance problems that
could arise are obviously endless.
9.3.1 General
All buildings have a number of "enemies" which are the root causes of maintenance
being required, and even in certain instances contributing factors in building failure,
leading to maintenance being prematurely required.
Of great importance is to have these “enemies” uppermost in mind when designing,
constructing and eventually maintaining a building. Primarily it boils down to
attacks by nature and human conduct. The influence which the following will
exert over time calls for critical awareness, from design to demolition:
Soil conditions
The building and the soil which supports it should always be thought of as a
"unit". This means that whatever happens in or to the soil, will influence the
building. A building is "founded" on the soil below, making it an integral
foundation element determining the well being and behaviour of the building
in future.
‫܀‬
Water
Be it ground, water or rain, the effect of it on buildings is not unlike the effect
of water on the well being of a ship. A ship is always under threat of water
entry. In fact it seems as if a ship is continuously trying to commit suicide.
A building is much the same. If water enters a building in an uncontrolled
fashion, it will cause maintenance problems. Ground water is everywhere
and one should assume that it will always try to enter buildings, pipes, cables,
etc. It not only attempts to enter elements of the building but often carries
with it agents that viciously attack the building, such as acids. Grime inevitably
enters with water, leading to staining and clogging of openings.
Surface water in turn penetrates building finishes, roofs, claddings, packings,
waterproofing, etc. It expands when it is heated or frozen and forces open
and breaks up elements which allowed it in. Stormwater brings with it forces
which sometimes sweeps reas clean or can even collapse entire buildings.
Wind
The wind is relentless in its efforts to loosen up elements of buildings, shakes
it, drives water into it and even scours it with particles which it carries. Wind
is very unforgiving where the opportunity presents itself to rip buildings apart
and to drench it in water. High winds are often accompanied by heavy rain,
which severely tests the ability of a building to survive, particularly over time.
Sun
The sun is even more relentless in its attack on buildings. It heats up the
surface elements of buildings, causing expansion, followed by contraction
over night. Sudden rain aggravates contraction by accelerating the cooling
time. The ultraviolet rays breaks up finishes and deteriorates all surfaces.
Cracks appear in elements and finishes which in turn permit water and grime
to enter, ever forcing the places where it entered more open, leading to
crumbling of areas or dislodging of elements.
Time
Although time has no physical presence, it should be kept in mind constantly
as it represents the speed at which maintenance will be required, translating
into the cost thereof. Over time, elements have the opportunity to attack.
The train of thought should always be “how will this element of the building
behave over time, being subjected to normal use, abuse, soil conditions,
water, wind and sun".
If something is required to last for only a short period of time due to expected
alterations, it is obvious that it will be viewed differently from an element which
has to last indefinitely.
Abuse and use
Buildings are, unfortunately, often a target for vandalism. Public areas are
particularly prone to vandalism whilst it is often found that even employees/
occupants in excellent office environments “vandalise” buildings through the
burning of carpets, damaging of wall papers, dirtying painted surfaces, fiddling
with electrical and mechanical components, theft of iron mongery, etc.
The designers and owners should discount the above possibilities in the
design, materials specified and by carefully considering the impact which
will be caused by the occupants and users of the building.
Normal use will result in deterioration over time. It could, or should, lead in
the first place to pleasing “aging" where possible and to maintenance within
acceptable tolerances.
Cost effectiveness
The life expectancy of, and the return on investment in a building, can be
enhanced substantially by the following: Ensure that the designer of the building is fully versed on the
quality
requirements of the client.
Subject the design to a conscious evaluation regarding the effect that
soil conditions, surface and rain water, wind, sun, abuse and use, and
time as a aging phenomena. The objective should be to "design
maintenance out”.
Although it is a fact that the level of maintenance and failure of buildings
are largely determined by design and workmanship, there is no
justification to use poor materials. The cost of labour as a percentage
of the total building cost is so high (at least 50% average and for
certain trades as high as 90%), that there is no justification for the use
of inferior materials. Only a very small initial saving will be obtained by
using low quality materials. Whilst the short term finished product may
appear to be sufficient, the long term maintenance cost, or even cost of
failure, will far outweigh the savings made on cheap materials. It does
not automatically follow that "expensive" materials should be used, but
it does require that the correct material of the right quality is used.
Maintenance is the Cinderella of the building industry. Furthermore it is
a "mental” thing that people leave the problem for someone else when
the creator of the problem is long gone. What is required is a change in
attitude which requires that the importance of maintenance and the proper
execution thereof is placed in its true perspective. The maintenance of
buildings should be regarded as similar to maintaining personal health.
When building work in general, and maintenance work in particular, is
done, it is of utmost importance that the instructions of manufacturers
are religiously followed. It is dangerous to assume that one "knows”
how to use a product, particularly a new product. Product improvement
takes place continuously and new products enter the market all the time.
To complicate matters it is found that different manufacturers offers
identical products with different trade descriptions. A "silk” finish from
one manufacturer could be identical to a "suede” finish by another.
The solution lies in studying the various products before it is used and,
when it is used, to check the instructions. Something could have changed
since it was last used. When costly failures occur, the first aspect that
will receive attention when a claim arises, is whether the instructions
were followed. The manufacturers usually wins the day on the latter
issue.
Before a building is even designed, the client needs to take a clear
stand on cost, quality, life cycle and return on investment. Although
good design, workmanship and materials should never be neglected, it
is obvious that different "levels" of quality can be specified, which will
translate into economic life expectancy and cost of maintenance along
the way.
9.3.2 Soil types
No building work, or even design, should be undertaken before a professional
soil investigation has been done. Soil conditions are a prime source of future
maintenance problems and failure, and it is of paramount importance that it is
adequately dealt with during the design stage in order to prevent maintenance
problems.
Maintenance problems are caused over an extended period if the soils keep on
moving (clay) or if settlement takes place over a long period of time, as is possible
when the water-table settles or the soil is compacted under the foundation over
time.
9.3.3 Foundations
Foundation movements, resulting in cracking, leaks, finishes breaking-up, etc.,
are usually of a serious nature and very expensive to rectify, if at all possible.
Movement can result from:
loading exceeding foundation or soil bearing capacity.
soil types that move.
trees in close proximity to buildings.
organic materials in soil.
earthquakes.
design errors.
settlement of buildings. mining activities.
Foundation movements can be addressed in various ways, depending on the
cause of the movement. Some solutions could be to:
remove surface water around buildings with water channels, sloping paving
and agricultural drains.
remove trees.
underpin foundations with piles or new strip foundations.
shore buildings.
9.3.4 Wall cladding
Movement in wall cladding (brick, plaster, stone, metal, glass, pre-cast concrete,
etc.), is to be expected and designs should allow for it. The following aspects
are particularly likely to cause problems: Thermal movement exceeding the ability of the material
and/or jointing to
accommodate expansion and contraction.
Inability of cladding to carry imposed loads.
Water, wind, grime entering between components.
Condensation between cladding and main structure resulting in dampness. Failure of cladding material.
The above failures could result in the cladding breaking up, leaking, staining and
even total collapse.
Remedial work could entail the following: Providing sufficient expansion joints by cutting-in or refixing
sections of the
cladding with adequate joints.
Resealing of joints.
Replacing cladding in total.
As a general principle cladding should be weatherproof and should have
adequate expansion joints.
9.3.5 Face brickwork
The most common failures in face brickwork are the following:
Structural cracking due to foundation movement.
Deterioration of joints, usually subscribed to a weak mortar (or soil/foundation
movements).
Efflorescence, causing a powdery deposit of salts on the surface area.
Surface crumbling resulting from poor quality bricks or frost action.
Staining, resulting from metal deposits or salts in the bricks.
Face brickwork can be repaired/covered in a variety of ways:
Structural cracks can usually only be fixed by ensuring that the structural
movement has been contained and by rebuilding the wall, preferably with
expansion joints.
If the wall is not breaking up along the joints, necessitating demolition, the
joints can be raked out to a depth of 20 mm, or to where the mortar is of
sufficient hardness, and be repainted.
Efflorescence can be washed-of occasionally until it disappears.
Surface crumbling can be stopped by removing all loose particles, whereafter
a sealer, paint, plaster or a cladding is applied.
Staining can be removed by the use of suitable light chemicals and scrubbing.
9.3.6 Structural steelwork and other metals
Structural steelwork is subjected to a large variety of stresses and attacks which
influences the durability of steelwork, notably the following: Movement due to compression and
settlement of foundations, thermal
movement, variable loadings and wind pressure.
Excessive stresses are created in structures which are slightly out of the
design “lines and angles”, insufficient grouting under base plates and forcing
structures to “fit" where workmanship is poor.
High alumina cement attacks steelwork, causing excessive corrosion.
Corrosion caused by rusting and chemical attack, the latter particularly in
industrial and city environments.
Dissimilar metals which are in contact with each other may cause electrochemical bimetallic corrosion.
When unavoidable contact occurs, metals
should be insulated from each other by non-conducting materials, or besealed with a protective coating
of suitable paint.
Generally corrosion of metals used in buildings may lead to the following defects: Complete loss of the
material
Structural soundness reduced
Distortion and cracking of other building materials
Causing unsightly surfaces
Leaking
The life expectancy of structural steelwork can be substantially extended by:
Proper design and erection.
Protection from the elements and other attacks by keeping it clean and
properly painted at all times.
Aluminium and stainless steel products are generally maintenance free as they
are corrosion resistant if the correct application is made. They can be adequately
maintained by cleaning with normal household detergents.
9.3.7 Timberwork, joinery and shopfitting
Timberwork, joinery and shopfitting should be undertaken only with woods that
have been well seasoned; the latter referring to wood that has been dried, reducing
the moisture content to the same level as the humidity of the air in which it will
be used. If this is not adhered to, undue shrinking or expansion will occur after
installation, leading to cracks or moving elements like doors getting stuck to
frames. Wood is grouped into hard woods (mainly broadleaved trees) and soft
woods (mainly needle-leaved trees).
The following defects occur in wood:
Natural causes: knots, shakes, bark pockets, dead wood and resin pockets.
Due to seasoning: check, ribbing, split and warping.
Due to manufacture: chipped, tool damage, waney edge.
Fungal attack: decay, dote, dry rot, wet rot.
Insect attack: wood-borers and termites.
Repairs to woodwork normally mean that it is to be replaced under serious
conditions, with the possibility of “patching" and redecoration when of a superficial
nature. The general principle applicable to woodwork is that it must be protected
from attacks by “preservation”.
The following preservatives can be used, depending on the severity of the
environment in question: Protective liquids such as toxic oils, creosote, water-borne salts (copper,
chrome or arsenic), and organic solvent solutions. These liquids may be
applied by brush, spraying or immersion. A preferred method for lasting
preservation is to obtain deep penetration by pressurised application in a
closed cylinder. Woodwork under attack usually needs several applications
of protective liquids to break the cycle of attack.
On joinery and shop fitting elements, treatment with oils, paints, varnishes,
poly-urethane, etc., are adequate to protect and rejuvenate timber.
Moisture and water should be kept away from woodwork if at all possible.
9.3.8 Solid floor coverings
A wide variety of solid floor coverings are in use. The following types (and their
maintenance) are commonly found: Granolithic and terrazzo finishes: These finishes are prone to
forming “loose
patches" leading to crumbling and can only be fixed by cutting it out in clean
square or rectangular sections for repairs. It is best maintained by regular
washing, a task which can be largely simplified by applying a permanent sealer
to the surface area. This substantially reduces the cleaning time, eliminates
dust from wear and prevents water and other liquids from entering the flooring,
causing deterioration and stains.
Terrazzo and clay tiles should be treated in the same fashion as above. Solid
bedding of tiles is a prerequisite for an extended lifespan.
PVC tiles, thermoplastic coverings, rubber flooring and cork are all laid in an
adhesive and can be chemically sealed for easy maintenance. Rolls of
carpets with glue seem joints are laid on an underfelt and stretched wall to
wall with smooth-edge strips along walls to retain the stretch. Various carpet
raw materials, ranging from wool to completely synthetic are available.
Carpets can be treated chemically to make them stain resistant and easier
to clean. For daily maintenance vacuum cleaning is the preferred method,
with steam cleaning or shampooing when necessary.
9.3.9 Plasterwork
Plaster is probably the finish that is most commonly used in traditional buildings.
As such it is an important element and requires more in-depth analysis. Seely
(1987:150-152) gives a self explanatory table (abstracts only, altered for local
circumstaces) showing plastering defects, their causes and remedies in table 9.1.
Table 9.1 Some plastering defects and their causes and remedies
Defect
Haircracks
Fine hair cracks on the
finished plaster
Cause
Remedy
Use of loamy sand and/or Filling of hair cracks can be done
excessive trowelling during with crack filler, or apply
finishing-off. wallpaper. Any "fixed" covering
Applying final coat before such as timber panelling can
initial shrinkage of undercoats also be used in severe cases.
is complete (if undercoats
are based on cement or
lime).
Shrinkage
Clearly defined cracks. Poor treatment of joints.
Cracks following a definite Shrinkage, settlement or
line, particularly with thermal movement
plaster on building boards
(partitions)
Adhesion
Loss of adhesion
Slow setting plaster
Plaster sets too slowly
Rake out and fill with crack filler
after stabilization of crack. In
some cases cracks are liable to
reappear and repairs should be
postponed for as long as possible.
Reinforce plaster with scrim or
metal mesh. Fill crack with
acryseal where future movement
is expected and paint over.
On gypsum undercoats -a If the undercoat is too weak the
strong final coat over a very only cure is to strip and replaster.
weak undercoat. If the undercoat is sound, strip
On cement or cement: lime the final coat, allow the underbased undercoats - applying coat to
thoroughly dry, roughen
final coat while undercoat surface, remove dust with damp
still 'green' and/or inadequate brush and replaster. Strip the
mechanical key. plaster, clean thoroughly and
Plastering over dirty surfaces, replaster.
particularly concrete. Treat the surface with one or two
coats emulsion bonding agent if
there is any doubt about a
satisfactory bond.
An unsuitable sand can extend Test the sand and change if
the setting time of a sanded necessary. With sanded mixes
plaster to 12 hours, whereas the setting time will increase as
the setting time with a stand the proportion of sand is
ard sand is about 3 hours. decreased.
continued...
BUILDING PRACTICE – VOLUME 2
Defect
Dry out
Plaster surface soft and
powdery with fine cracks
Efflorescence
Soluble salts on plaster
face
Sealed-in-water
Moisture trapped in new
plaster
Mould growth
Surface staining
Flaking and peeling final
coat
Loose patches
Cause
Plaster drying before setting.
Plaster coat of insufficient
thickness.
Remedy
Use the correct grade of plaster
applied to the correct thickness.
On work already plastered the
only remedy is to strip and
replaster.
Soluble salts brought forward Dry bush the surface carefully
from the background to which and repeatedly as the salts
the plaster has been applied, appear. The salts should be
to the face of the plaster as swept up and thrown away.
the building dries out. Good ventilation will hasten the
drying process. Decoration is
best delayed until the structure is
thoroughly dry; if this is not
practicable use a permeable
paint suitable for early decoration.
Much of the water used in
construction can be retained
in the structure for a
considerable time. Wet
plaster should not be sealed
with impermeable finishes.
Use permeable paints to allow
the moisture to evaporate and
facilitate proper drying out. If
impermeable paints are to be
used, the walls must be allowed
to dry out thoroughly.
The growth starts in minute Once the structure has dried out
windborne spores which alight the growth will stop. Any existing
on and develop in the newly mould and decoration should be
applied coating. The spores scraped off the surface of the
will only develop if sufficient plasterwork. When dry, the
dampness is present. affected area should be treated
with a fungicidal wash, keeping
the work dry and ventilated.
Persistent moisture penetration through the background.
Strip defective plaster and
provide positive barrier to
dampness.
/continued...
Defect
Irregularity of surface
texture
Uneven texture
Popping or blowing
Small bulges or little
craters
Recurrent surface
dampness
Wet surface areas
Rust staining
Brownish stains, often
with cracks in it
Softness or chalkiness
Powders when handrubbed
Cause
Remedy
Uneven trowelling or marked Apply an additional coat of plaste
differences in suction of back to obtain smooth surface.
grounds due to the different
suction from bricks, blocks or
concrete.
Particles in the background Fill with crack filler after properly
or in the plaster, lime or sand having cleaned the defective
which expand after thearea and redecorate.
plaster coat has set.
Deliquescent salts attract
moisture from the air. They
can result from the use of
unwashed sea sand, and be
carried from the background
in to the plaster by, say,
condensation in an unlined
flue or shaft.
Strip the plaster and provide an
impervious barrier before
replastering.
Application of unsuitable Strip the plaster and replaster
plaster to metal lathing or with lathing fixed over the area.
plaster in contact with Metallic conduit or channeling
corrodible ferrous metal in have to be painted to prevent rust
persistently damp conditions. and positioned sufficiently deep
Rusting reinforcing located below the surface to prevent
too close to the surface. cracking of plaster. Reinforcingshould have sufficient cover or be
sealed over with an epoxy
plaster.
Excessive suction or thinness, Adequate wetting of backing
or exposure to excessive heat before plastering, use of a
or draughts during setting. bonding agent, proper applicationof a final coat of adequate
thickness, or use of a special
type of plaster.
9.3.10 Paintwork
Paintwork is regarded as being of a good quality when it displays the following
features:
Attractive, evenly coloured with uniform finish, covering the surface fully.
Neatly "cut in" where the painted elements adjoins other painted or unpainted
elements.
The cover must obliterate all underwork or previous paintwork.
No defects must show in the finished product.
It must be able to protect the components painted from the elements for an
extended period. Normal cleaning operations should not damage the painted surface.
Maintaining paintwork at a high level requires that a reasonable repainting cycle
should be adopted. To repaint rather sooner than later is cost effective because it
is extremely labour intensive and thus expensive to prepare a badly deteriorated
surface for redecoration. The labour cost involved in painting, makes it shortsighted to use an inferior
quality paint.
When repainting woodwork the following aspects should be carefully attended
to:
Chalky previous paintwork should be thoroughly washed or sanded down
before repainting.
Cracks, knots and other damage should be cleaned and filled with a
suitable stopping and sealed with a primer.
The woodwork should be dry and clean before repainting.
Any previous paintwork which is pealing, flaking or suspect in any way
should be removed before repainting is done.
All metal fixings, such as nails and screws, in timberwork are to be paintedwith a metal primer to
prevent rust spots in the final finish.
When repainting metalwork the following aspects should be carefully attended
to:
Do not delay beyond the appearance of the first rust marks.
Clean the surface properly, remove all rust and treat with a primer.
On steelwork old paint can be removed with steel wire brushes, blowlamps,
scrapers and sandpaper.
Specific care should be taken that welded joints, crevices, bolts, etc. are
cleaned extremely well and thoroughly painted as it is particularly prone to
rust and chemical attack.
In severe cases of rust, sandblasting may be required to strip the old paint
completely and to remove rust which has penetrated the surface area.
On softer metals such as aluminium and copper care should be taken not to
damage the metal through aggressive cleaning.
When repainting plastered walls and ceilings the following aspects should be
carefully attended to:
Rub smooth, or powdery surfaces, down to a matt surface to receive new
paint.
Dirty surfaces must be cleaned thoroughly.
Repair all defects and make sure that the causes of any dampness areremoved before repainting.
General aspects for all types of repainting to be attended to are the following: Paintwork will not be
successful if the surface area is oily, flaky, dusty or has
any substance on it that causes a barrier, however thin, between the new paint
and the surface to be painted. Never do any paintwork without thoroughly
cleaning the surface to be painted.
Paint is a chemical product. It is therefore important that the area to be
painted and the various layers of paint to be applied, must be compatible. It
is most important not to take any chances but to check with paint manufacturers
that the correct product types are used to ensure a sound final product.
Always use clean brushes, rollers, sponges and other tools of application.
Clean surfaces, clean (dirt/dust free) paint and clean tools will help to ensure
a quality finish.
9.3.11 Plumbing and drainage
Plumbing and drainage are important and expensive components of any building.
High quality installations will display the following properties: The design and selection of materials will
be done with great care.
The installations will be done with care with particular emphasis to ensure
that maintenance can be done easily. This implies that services should bereadily accessible with
adequate working space.
Typical problems and solutions in pipework and drainage are the following: Some water corrodes pipes
faster than others, making it necessary to ensure
that suitable pipes for the area are chosen.
Do not use different types of metal pipes in the same line as it may cause
chemical reaction and corrosion.
Pipes must be securely fixed.
Leaking taps and faulty ball valves cause corrosion and staining of sanitary
fittings and must be replaced.
Place stopcocks in obvious and easily accessible areas.
Pipes should be lagged where temperatures drop below freezing point or
where heat loss as to be prevented.
BUILDING PRACTICE
VOLUME 2
Water hammers should be rectified as it may lead to pipe bursts and valve
damage. This may require the installation of bigger feeder pipes and air
relief valves.
Airlocks may be caused by dips and falls in pipe work. Air gets trapped in
the high points. This may cause poor flows, and water hammers. Pipes
should rise slowly towards vent pipes to ensure escape of air.
Drainage with too shallow or too steep a fall will tend to block, either due to
insufficient flow in the pipe or segregation of solids due to the water draining
too rapidly. This problem can only be solved by relaying of the drains.
If drainage pipes are angled incorrectly or are too small in a stack system,
there will be continuous problems with blockages. This can only be rectified
by redoing the system with bigger pipes.
9.3.12 Flat roofs: concrete slabs
Flat roofs are generally found in concrete structures where the top slab is the
"roof slab”. The waterproofing of this slab presents a number of important
aspects which have to be dealt with to ensure satisfactory performance. The
following being the most notable:
The type of waterproof “membrane" has to be carefully chosen. The following
types are typically used: Hot mastic asphalt, applied by trowel, finished in bitumen aluminium paint.
Malthoid/Derbigum sheeting, laid with laps and hot sealed, finished in bitumen
aluminium paint.
Butyl rubber sheeting, with the overlaps sealed with contact adhesive and
finished in a rubber-based paint.
Acrylic cloth laid in an acrylic emulsion base with overlaps, drenched with
acrylic emulsion, and acrylic paint applied by brush as final finish andcolouring
Typical construction entails the laying of a lightweight screed with falls to outlets
to receive the waterproofing. This screed must have a very smooth final surface
to prevent puncturing the waterproofing and is normally laid on top of high density
fibreglass or polystyrene thermal insulation. The insulation can also be placed on
top of the screed or even on top of the waterproofing (usually polystyrene covered
with pebbles or loose laid tiles to keep in down), but this is not recommended.
Tiles may be loose laid on pads or bedded in mortar, over waterproofing.
Problems which typically cause leaks are the following: The waterproofing itself, or lap joints fail. Poor
workmanship and a lack of
maintenance are the main contributing factors.
Roofs are subjected to extreme variation in temperature with expansion and
contraction taking place. This could tear the waterproofing, result in cracking
or in the case of tiles laid over waterproofing, cause abrasive movement of
the tiles on the waterproofing resulting in damage.
The most common cause of leaks results from poor wall flashing, sealing
around pipes and other protruding elements as well as dressing of
waterproofing into outlets. Flashing work should be an integral part of the
waterproofing and not just "stuck-on".
Design faults, often resulting in situations where it is difficult to do the
waterproofing properly in the first instance, result in permanent problems
Solar radiation and ultraviolet rays are serious enemies of waterproofing and
keep it under constant attack.
Damage due to walking on roofs is a common cause of leaks and should be
kept to a minimum.
Maintaining and repairing waterproofing on flat roofs involves the following: Waterproofing normally
carries a ten-year specialist's guarantee. This
guarantee specifies maintenance requirements during the ten years, with
particular emphasis on the repainting of waterproofing. Waterproofing that
is regularly inspected for defects, and painted every three years, gives fairly
reliable service.
Finding the origin of leaks in flat roofs is often very difficult. The water
which penetrates through the waterproofing can seep along the roof slab for
substantial distances leaking eventually at a weak place in the slab or at
expansion joints. By forming temporary dams (with say sand barriers) on the
flat roof, the roof area can be systematically checked for the point of entry.
It could however take several hours before the actual leak shows up. Flashing
and other turn-ups are normally subjected to careful visual inspection.
Repairing flat roofs is a matter of resealing the original material with the
same material. The use of a different material for repairs is normally only a
temporary solution, failing after a relative short period of time.
9.3.13 Plastics
Plastics are in common use in many finishes in buildings and are used
comprehensively in pipework, conduiting and electric wiring. In the normal cause
of events, plastics which are visually used is easy to maintain by cleaning it with
ordinary household detergents.
Maintenance problems with plastics are mainly caused by aging, whereby the
plasticiser in the material dries out, leaving it brittle and prone to breakage.
Once plastic products have reached this stage the only solution is to replace it.
Ultraviolet (sun) can shorten the life of plastic products substantially. It is important
to note that plastics intended for external use should be those manufactured
with a high ultraviolet resistance. Too often however, due attention is not paid to
this particular aspect and plastics intended for internal use (usually pipework)
are used externally with a much reduced life expectancy.
9.3.14 Flood damage
Flood damage to buildings will of necessity range from severe to superficial.
In the case of severe flood damage it may in fact lead to the destruction of the
building or damage to the extent that demolition has to be considered.
In less severe cases the damage can be classified into three categories:
Permanent damage to components and finishes which cannot be dried out
or repaired.
Finishes that can be restored by redecoration.
Building elements that can simply be left to dry out and then be cleanedwhere necessary.
The severity of the situation and the cost involved in restoring the building for
further use will determine the action to be taken.
9.3.15 Dampness and condensation
Dampness in buildings is mainly caused by the following factors:
Water introduced during building operations by wet trades and rain. The
period it takes to dry out will depend on the particular situation but could be
a source of dampness for an extended period.
Penetration of rainwater through leaking roofs and walls.
Leaks in the plumbing system could range from small damp patches to free
water.
Rising damp is a serious problem, often difficult to fix, which could occur in
floors and walls, mainly due to insufficient damp proofing being provided tobreak capillary action.
To cure dampness in buildings it is necessary to isolate the cause thereof and to
remove it. Obviously there are a multitude of possibilities which may require
expert knowledge and support.
Condensation in buildings is mainly caused by a number of factors:
Warm air contains more moisture than cold air. When warm moist air comes
into contact with a cold surface condensation is formed on that surface.
Wherever these conditions are created in a building, condensation will take
place with the resultant dampness which can cause serious problems.
Pockets (rooms) of air containing more vapour than the surrounding areas,
has a higher vapour pressure and hence the moisture escapes to the drier
air. In practice this means that the wetter air disperses to other areas,
penetrating into fabrics and even building materials. All available routes will
be followed and moisture will manifest itself as water or dampness on cold
surfaces and in slightly porous materials.
The generation of steam, the air breathed out by occupants, washing of
clothing, hot bath and shower water, all produces moist air leading to
condensation and vapour pressure.
Condensation causes unsightly mould growth, dry rot in timber, rusting of
steel, staining, etc. It is accompanied by a musty smell, particularly where
fabrics and building materials have been penetrated.
Remedial measures that can be adopted are:
Sufficient ventilation to remove moist air.
Insulation to keep surface areas above dew (condensation) point.
Heating the interior of the building to keep surface areas warm enough to
prevent condensation.
Use of damp proofing, usually plastic strips and sheeting to stop capillary
action.
QUESTIONS FOR SELF-EVALUATION
1.
2.
3.
4.
Distinguish between building failure and building maintenance
and explain how you will deal with it respectively in practice.
Discuss the various types of building maintenance, using a
diagrammatic presentation as guideline.
Which building "enemies" that give rise to maintenance problems
should be considered as the root causes thereof?
Discuss the causes of maintenance problems regarding five
building elements and indicate how it could be dealt with in
practice.
REFERENCES
(25)
(25)
(25)
(25)
100
Seely, I. H. 1987. Building maintenance. Southampton: Macmillan Education.
ESTIMATION OF BUILDING
COSTS
CONTENTS
10
LEARNING OBJECTIVES
10.1 INTRODUCTION AND OVERVIEW
10.2 ESTIMATING OF BUILDING COSTS THEEMPLOYER (CLIENT)
10.2.1 Introduction
10.2.2 Cost-per-unit method of estimating
10.2.3 Square-metre method of estimating
10.2.4 Storey-enclosure method of estimating
10.2.5 Rough or approximate-quantities method of estimating
10.2.6 Elemental method of estimating
10.2.7 General
10.2.8 Estimating total capital outlay (TCO) on a project
10.3 ESTIMATING TOTAL COST OF A BUILDING OR FACILITYIN USE OVER ITS LIFETIME
10.3.1 Lives of buildings
10.3.2 Life-cycle costing
10.3.3 Relationship of capital, maintenance and running costs
10.3.4 Difficulties in assessing total costs
10.4
10.5
10.6
COST BUDGETING
COST CONTROL
CONTRACT PRICE ADJUSTMENTS
10.6.1 Introduction
10.6.2 Fixed price contracts
10.6.3 Proven costs contracts
10.6.4 Contract price adjustment provisions of the JBCC
QUESTIONS FOR SELF-EVALUATION
REFERENCES
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LEARNING OBJECTIVES
The objective of this module is to provide the student with a basic
knowledge of the methods and tools used to ensure that building projects
are completed within the approved budget.
10.1 INTRODUCTION AND OVERVIEW
In chapter 1 (section 1.3, p.6) building is characterised as a production process
involving the conversion of inputs into outputs. Inputs can also be referred to as
the resources needed for the process.
These resources are relatively scarce, that is they are not freely available in
nature, and usually come at a certain cost. Their use in the building process
therefore, has to be carefully managed. This includes looking after the costs of
using them, which involves the following major processes: Resource planning: determining what
resources (people, equipment,
materials) and what quantities of each should be used to perform project
activities.
Cost estimating: developing and approximation (estimation) of the costs
of the resources needed to complete project activities.
Cost budgeting: allocating the overall cost estimate to individual work items,
and projecting the expenditure over time.
Cost control: ensuring adherence to, and controlling changes to the projectbudget.
When a building project is performed under contract, care should be taken to
distinguish cost estimating from pricing. Cost estimating involves developing an
assessment of the likely quantitative result – how much it will cost the performing
organisation to provide the product or service involved. Pricing is a business
decision – how much will the performing organisation charge for the product or
service – that uses the cost estimate as but one consideration of many.
In building projects, cost estimating and pricing respectively usually take place at
two levels. In the first instance, the project initiating body (employer or client)
requires cost estimates in order to decide on the financial feasibility of the project
and will then "price" the building(s) for sale or letting, using the cost estimate as
one of the considerations in setting the selling price or rental as the case may be.
One of the major components of the total project cost estimate is the building cost
which at some stage may be based on a “tender price” submitted by a contractor.
In order to arrive at a tender price, the contractor in turn has to estimate the cost
to him/her of producing the building(s) under contract.
The final cost (or price) of a building project is made up of a cost to price chain
which involves land, the suppliers of raw materials, manufacturers of products
and processed materials, labour, subcontractors, the main contractor, finance
and other service providers and lastly the client. In this chain the price (output)
of one link is usually the cost (input) to the next link.
10.2 ESTIMATING OF BUILDING COSTS FOR THEEMPLOYER (CLIENT)
10.2.1 Introduction
Estimating the cost of a building is the means determining the probable cost of
that building where either there is not sufficient detailed information available about
that building (e. g. at sketch-plan stage), or the obtaining of exact information would
be too tedious and time-consuming to serve the purpose (e. g. on existing buildings
valued for insurance purposes).
The cost of a building is usually estimated as at the present time and under
prevailing building-market conditions. It is possible however, to determine the
estimated cost of a building at any time in the future by making assumptions about
the rate of escalation of building costs due to inflation, and the likely prevailing
market conditions at that time, and then compounding the present cost of the
building by the necessary factors.
There are a number of methods of drawing up an estimate. Each specific method
serves a particular purpose and requires different kinds of information. Where
for example, only a rough indication is required, the "cost per unit" method of
estimating could be used. At the other end of the spectrum a highly accurate
estimate of cost can be obtained by pricing out a detailed bill of quantities. All
cost estimating methods require some form of quantification first, that is taking the
type and the quantities of work to be done off the drawings and specifications
(taking off = measuring quantities).
The various methods of estimating are dealt with in more detail below.
10.2.2 Cost-per-unit method of estimating
The cost-per-unit method of estimating is an extremely rough and rather unreliable
method of estimating. It consists of multiplying the use-factor of a building (such
as the number of flats in a block of flats, the number of seats in a church, the number
of children to be accommodated in a school, the number of persons to be
TD
102
accommodated in an old-age home, etc.) by a monetary rate, thereby obtaining
an estimate of the total building cost.
This method can be used to give a very rough indication of total cost, and may
also be employed for setting a target or cost limit (cost norm).
An example of the use-factors employed for setting a cost limit for a hospital is
as follows:
Ward block
Out-patients section
Kitchen block
number of beds
number of out-patients that could be treated in that
section per day
number of meals to be served per day
These use-factors are multiplied by a predetermined monetary rate usually based
on comparable historical records, and an estimate of total building costs is then
arrived at which could become a cost limit after due allowance has been made
for factors such as special site conditions, difficult foundations, etc. These cost
limits should be updated from time to time to allow for increases in building costs.
It could also serve as a target or cost limit which may not be exceeded by the
professional team and forms part of their brief.
10.2.3 Square-metre method of estimating
This is a method which has been employed for many years, and is still in general
use. It consists of multiplying the total construction area by a monetary rate,
thus obtaining an estimate of building costs. The costs of all external paving,
yard or boundary walling, other external works and any items of exceptional
value are separately calculated. The monetary rate is based on recent or
concurrent rates for comparable buildings.
In an attempt to standardise the method of measurement of construction area,
the Construction Economics Committee of the Association of South African
Quantity Surveyors has defined the term "construction area” in their "Guide to
Elemental Cost Estimating and Analysis for Building Works, 1998” as follows:
“The construction area of a building is the total of all the areas of a building
measured on plan at each covered floor level over the external walls of the
outermost vertical enclosing planes or, where applicable, the centre line of party
walls between buildings"
The following items are specifically to be included in the calculation of
Construction Area:
Internal stairwell and staircase areas
Lift shaft areas
Duct space areas
Mezzanine floor areas
Finished floor areas in attic spaces
Floor areas to penthouses, staff quarters, lift motor rooms, etc.
All open but covered porches, balconies and balcony corridors within the
enclosing planes of the main building
Floor areas to attached sheds, carports, etc. and all partially completed
rooms, porches, balconies, etc., provided the relevant areas are covered
and have at least two of their walls not less than two-thirds of the storeyheight on which they occur
The following items are specifically to be excluded in the calculation of
Construction Area:
External steps and paved areas
Areas of projecting roof overhangs, hoods, and canopies and the like
Enclosed open areas (light or ventilation, wells and courtyards)
Areas of open covered ways and carports, etc.
Areas of unenclosed fire escapes
Areas of small projections such as pilasters, attached piers, fins, chimney
breasts, etc.
The areas of different types of buildings within the same overall building project,
such as the office block of a factory project should, as far as possible, be kept
separate from each other.
The following is a diagrammatic plan of a block of flats, together with an
example of a square-metre estimate of building costs:
K
45 000
2000
Figure 10.1 Diagrammatic plan of a block of flats
11 000
BUILDING PRACTICE – VOLUME 2
Ground floor: Underblock parking except entrance hall of 3,0 m x 4,0 m plus2,0 m x 3,0 m and staff
quarters of 3,0 m x 10,0 m.
Typical floors: 6
Lift motor room: 2,0 m x 4,0 m
ESTIMATE OF BUILDING COSTS OF NEW BLOCK OF FLATSFOR D SWANEPOEL, ESQ.
(BASED ON DRAWING NO. 58/91)
6/45,0011,00
6/2,003.00
3,00
4,00
2,00
3.00
3,00
10,00
2,00
4,00
Item
6 Floors
6/6
45,00
11,00
2,00
3,00
Deduct3,00
4,00
2,00
3,00
3,00
10,00
2 970,00
36,00
6.00
3 024,00
30,00
8,00
495,00
6,00
501,00
12,00
6,00
30,00
48.00
453,00
Lift
Flats including corridors,
stairs and entrance hall
3 024 m2
30 m2
Staff quarters
Lift motor room
8 m2
DATE: 25 JUNE 1998
R1 750,00
R1 500,00
R1 000,00
Fire escape staircase
6 No. R3 000,00
36 Stove's in Gauteng only)
36 No. R1 800,00
Under block parking
including concrete paving
453 m2
R 300,00
SUBTOTAL
R5 292 000,00
5 000,00
8 000,00
R 450 000,00
18 000,00
64 800,00
R 135 990,00
R6 013 700,00
53,00
2/52,00
53,00
2/52,00
45,007,00
3,00
29,00
2,00
11,00
53,00
104,00
157,00
53,00
104,00
157,00
315,00
87,00
402,00
22,00
SITE WORKS (calculate by rough quantities)
220 mm brick boundarywall 2 m high with
facings both sides andbrick-on-edge coping
157 mR320,00
157 m
Concrete in footings
for boundary wall,
including excavationR 60,00
Concrete paving (excluding
paving under building)
402 m2
R 55,00
Brick-on-flat paving onconcrete surface bed
22 m2R 90,00
Contingencies 2,5% (say)
TOTAL ESTIMATED CURRENT BUILDING COST
Rate per m2 (excluding site works etc.):
R6 013 700,003 515 m2
= R1 710,87 per m2
50 240,00
9 420,00
R 22 110,00
1 980,00
R 152 550,00
R6 250 000,00
This estimate is based on ruling competitive market conditions, and does not
allow for loose furniture, fridges or professional fees.
NOTES:
Estimators should record job reference (or job name), date and drawing
number(s).
Estimating to be qualified in respect of the fact that it is based on “ruling
competitive market conditions".
There are many factors which could affect or vary the rate used in a
square-metre estimate. The following are a few examples:
Fullness on plan
It is obvious that the rate per square metre for a block of flats with twobedroom flats only, will differ a
great deal from the rate for a block of
bachelor flats. To illustrate the influence of “fullness on plan”, examine
the following buildings:
2 000
4 m2
А.
2000
400 m2
20 000
B
20 000
Figure 10.2 "Fullness on plan" influence (buildings notto scale)
Assume that the superstructure walling for both these buildings is
3 metres high. Taking the external walling only, without making
allowance for deducts at corners, the position will be as follows:
Case A 8 mx 3 m 24 m2 of external walling at a rate of say, R140,00 per square metre (this allows for
external finish,
internal finish) and is equal to R3 360,00 or R840,00 perm2 on plan.
Case B 80 m x 3 m = 240 m2 at R140,00 is equal to R33 600,00 orR84,00 per m2 on plan.
There is a notable difference of R756,00 per m2 on plan.
Shape of building
Examine the following buildings:
400 m2
20 000
400 m2
A
100 000
B
Figure 10.3 Shape of building
20 000
4000
Case A External wall length 80 m
Case B External wall length 208 m
This is a substantial difference, considering that both these buildings
have the same construction area on plan.
Floor-to-ceiling height
It is obvious that the rate per m2 for a building of 3 m floor-to-ceiling
height will be lower than the rate for a building with 4 m floor-to-ceiling
height.
Height of building
The difference in the rate per square metre for a single or double-storey
building and that of, for example, a forty-storey building respectively
could be substantial. Horizontal wind loads for instance become a
marked factor in structure costs when buildings start exceeding twenty
storeys.
Constructional differences
For example, reinforced concrete walling instead of brick walling, or
hollow-tile slab construction instead of solid slab construction, or
industrialised building methods instead of conventional methods, etc.
Difference in finish and/or architectural detail
It is apparent that the rate per square metre will be substantially affected
if, for instance, marble floor slabs are used instead of granolithic floor
finish, or precast terrazzo cladding instead of bagging and limewash to
walls.
For the estimator employing the square-metre method of estimating, it is
fairly easy to assess the difference in rate for the horizontal components
of the building such as floors, ceilings, roofs, etc., and more difficult to
assess differences in the vertical plane since there is very little or no
relationship between the horizontal building area and the vertical
components of the building.
Sanitary fittings, joinery fittings, etc.
A concentration of toilets or sanitary fittings will make a substantial
difference in the rate per m2 of the building.
Site
The following are a few of the items which could affect the square-metre
rate:
Nature of foundations
Sloping or level site
Position of municipal sewer connection, resulting in excessive length
of drains
Access difficulties
Locality or area
Building costs vary considerably from place to place. In this respect,
mention should be made of the difference in building costs between
Pretoria and Johannesburg - traditionally approximately 10% although
it varies considerably from time to time.
Tender conditions
Factors such as the use of competitive or negotiated tendering methods
and the availability of tenderers, etc., will all influence the tender amount.
Negotiated contracts are invariably more expensive than open-tender
contracts in a competitive market.
Building-contract period
The shortening of the period for the completion of a building to much less
than that which could reasonably be contemplated will result in increased
building costs.
The square-metre method of estimating should not be employed, except
for preliminary estimates of building costs where block plans or rough
diagrams only are available. It is best used as a check on other systems
of estimating, and is also an aid to cost planning. It has become outdated
as an accurate method for detailed estimating, owing to the increasing
complexity of building methods and materials, and also the development
of more sophisticated estimating methods.
It is important to note that there are four basic rates per m2 which
are generally quoted namely: Basic building rate - excluding special items and site works and
general.
Example:
R1 500 000,001 000 m2
= R1 500,00 per m2
Building rate, i. e. basic rate plus special items such as specialist
work, mechanical work, etc. but excluding site works and general.
Example: R1 800 000,001 000 m2
Project rate
= R1 800,00 per m2
overall rate, including siteworks and general.
Example: R2 200 000,001 000 m2
= R2 200,00 per m2
Use factor rate -rate per usable or lettable area
Example: R2 200 000,00R2 588,24 per m2 of lettable area
850 m2
INB
BUILDING PRACTICE – VOLUME 2
10.2.4 Storey-enclosure method of estimating
This method of estimating consists of measuring certain areas such as the roof
area, the floor area, the vertical external wall area, etc. and multiplying each of
these areas by a factor predetermined for each component. The result thus
obtained is multiplied by a single common rate, thereby obtaining an estimate of
building costs for the structure, roof, floors and finishes of the building. Items such
as plumbing and sanitary fittings, joinery fittings, etc. are separately measured
and estimated.
This method is an attempted compromise between the shortcomings of the
square-metre method of estimating and the time required for the more detailed
estimating methods.
It is however, seldom used in South Africa mainly because there are no comparable
unit rates available.
10.2.5 Rough or approximate-quantities method of estimating
This is a method whereby the important cost items are measured in much the
same way as the items in a bill of quantities, except that items of identical or near
identical measurement are grouped together (e. g. although varying in exact area,
the areas of the floor finishes, screeds, surface beds, hard-core and earth filling
are sufficiently similar to permit them to be grouped together.
Sundry items of little value are not measured but are allowed for as a percentage
addition.
This method, although basically sound, has the following important disadvantages:
It is time-consuming and tedious.
Detailed information is required such as is usually provided only on working
drawings.
It is sometimes difficult to decide which items are sufficiently costly as to
require measurement e. g. is the cost of the skirting such that it may be
ignored or should it be measured detail?
Great skill and experience is required in judging the percentage of cost to be
allowed for sundry items.
Rough or approximate quantities can be successfully used in supplementing other
systems of estimating.
An example of a door measured in rough quantities is as follows:
DESCRIPTION
Extra over half-brick wall with
one coat internal cement plaster
and two coats PVA both sides,
for hollow core door with kiaat
veneer both sides, varnished,
with steel door lining with
standard steel butts, painted,
with two-lever mortise lock with
chromium-plated furniture, and
with screed and vinyl floor in
opening.
QUANTITY
1
UNIT
No
RATE
R183,95
AMOUNT
R183,95
The skill and experience of the estimator will determine whether he will build up
the price from basic prices or insert the total price, drawing entirely from his
experience of the prices of rough quantities.
Build-up of price in the example above:
Door
Varnish
Frame
Paint frame
Lock
Screed
Vinyl floor
Deduct
110 mm brick wall
Plaster
PVA
Sundries (say 5%)
1,6
3,3
3,3
Preliminary items (say 12%)
1
3,50
1
1,30
1
0,09
0,09
m2
m2
m2
No
m2
No
m2
No
m2
m2
R 45,00
R 13,00
R 9,80
R 90,0011,00
110,00
R 11,70
R 45,00
R 15,00
R 40,00
R 72,00
R 42,90R 32,34
SUBTOTAL
TOTAL
R 90,00
R 38,50
R 110,00
R 15,21
R 45,00
R 1,35
R 3,60
R 303,66
R 147,24
R 156,42
R 7,82
R 164,24
R 19,71
R 183,95
D
10.2.6 Elemental method of estimating
General
Of the methods discussed, the elemental method of estimating is considered
the most reliable, accurate and consistent.
For this method buildings are divided into elements, e. g. structural frame,
external facades, plumbing, etc. Each element is subdivided into components,
e. g.: concrete walls, other walls, external finishes, windows, window sundries
and external doors, steel and other similar expensive finishes or construction,
curtain walls. The method of division and sub-division is defined and
consistent for all buildings, thus facilitating the use of information obtained
for one building when estimating the cost of other similar buildings.
Thus, both when analysing the cost of an existing building and when
estimating the cost of a new building, each of the elements or components
is considered and evaluated in the plane in which it occurs: namely, the
external walling would be evaluated per square metre on elevation, the
concrete slabs per square metre on plan, strip foundations per metre and
sanitary fittings and plumbing per unit or point.
The following is an excerpt reproduced from the "Guide to Elemental Cost
and Estimating Analysis for Building Works” (1998) issued by, and available
from the Association of South African Quantity Surveyors. Students are
referred to the actual document for a complete schedule of elements and
components.
DEFINITIONS
1. SectionsThe elements are sub-divided into the following sections: Primary
Elements, Special Installations, Alterations, External Works and
Services, Training, Preliminaries, Contractor's fee, Contingency
Allowances, Escalation and Value Added Tax. Elements are defined
and constant for all buildings, thus facilitating the use of information
obtained from a building when estimating the cost of other similar
buildings.
2. ElementBuildings are divided into Elements (e. g. Foundations, External
Envelope, Roofs, etc.). An Element is that part of any building that
always performs the same function irrespective of its construction orspecification. Elements should not
be combined or divided.
3. ComponentEach Element is sub-divided into components (e. g. the Element Roofs
is sub-divided into the Components of Construction, Coverings,
Insulation, etc.). Where a specific Component forms a high cost part of
the estimate, such Component should be further sub-divided into subcomponents.
4. Measurements Required for Element or ComponentThe measurement required is the actual
quantitative unit of the Element
or Component. Each of the Elements or Components is considered
and evaluated in the plane in which it occurs (e. g. the Element Roofs
would be evaluated per square metre in the various planes of the roof,
the Component Downpipes per metre length and the Component
Dormers per unit number). The quantity of an Element or a
Component is measured and mutiplied by a monetary rate thus
obtaining an estimated construction cost for that Element or
Component
5. Unit
Unit denotes the unit of measurement of the individual Element or
Component.
6. Composition of Element or ComponentEach Element comprises various Components. Each
Component
comprises various parts or sub-components.
7. Taking off/Pricing NotesTakin off/pricing notes are guidelines to assist the estimator in the
taking off and pricing stages of an estimate.
8. CodeThe Code is the numerical identification for each Element of
Component
9. Cost
Cost is the cost of an Element and is the aggregate of the Component
costs comprimising the particular Element.
10. QuantityQuantity is the actual measured quantity of an Element or Component.
11. Cost Per Unit
Cost per unit is the cost of an Element divided by the measured
Quantity of the Element (e. g. the Cost of the Element Roofs divided by
the area of the Element Roofs).
12. Cost Per Square MetreCost Per Square Metre is the cost of the Elemental divided by the
Construction Area.
13. Cost (Percentage) %Cost % is the cost of the Element expressed as a portion of the total
cost.
14. Construction AreaThe Construction Area of a building is the total of all the areas of a
building measured on plan at each covered floor level over the external
walls or external lines of the outermost vertical enclosing planes or,
where applicable, the centre line of party walls between buildings.
The following are included in the calculation of Construction Area: Internal stairwell and staircase areas
Lift shaft areas
Duct space areas
Mezzanine floor areas
Finished floor areas in attic spaces
Floor areas to penthouses, staff quarters, lift motor rooms, etc.
All open but covered porches, balconies and balcony corridors
within the enclosing planes of the main building
Floor areas to attached sheds, carports, etc., and all partially
completed rooms, balconies, etc., provided the relevant areas are
covered and have at least two of their walls not less than twothirds of the storey height on which they
occur.
The following to be excluded from the calculation of Construction Area: External steps and paved areas
Areas of projecting roof overhangs, hoods, canopies and the like
Enclosed open areas (light or ventilation wells and courtyards)
Areas of open covered ways and carports, etc.
Areas of unenclosed fire escapes
Areas on plan of small projections such as pilasters, attached
piers, fins, chimney breasts, etc.
15. TrainingGovernment clients require the inclusion of an amount for training of
previously disadvantaged individuals. Training of candidates shall
consist of institutional training on a competency based modular basis
and practical on-site training under competent supervision provided by
the contractor.
SUMMARY OF ELEMENTS
The following new elements and components within the above sections
have been introduced:
Primary elements
Foundations
Ground Floor Construction
Structural Frame
Independent Structural Components
External Envelope
Roofs
Internal Divisions
Partitions
Floor Finishes
Internal Wall Finishes
Ceilings and Soffits
Fittings
Electrical Installation
Internal Plumbing
Fire Services
Balustrading, etc.
Miscellaneous Items
Special installations
Piling
Sun Control Screens, Grilles, etc.
Raised Access Floors
Special Fire Protection
Lifts
Escalators
Air Conditioning
Ventilation
Heating
Special Electrical Installations
Other Services
Compactors
Access Control
Gondolas
Stoves
Kitchen Equipment
Specialised Equipment
Security Systems
Communication Systems
Prefabricated Cold Rooms
Signage
Artwork
Miscellaneous Items
Alterations
Alterations
External works and servicesSoil drainage
Sub-surface Water Drainage
Stormwater Drainage
Water Supplies
Fire Service
External Electrical Installations
Connection Fees, etc.
Demolitions
Site Clearance
Earthworks
Boundary, Screen and Retaining Walls, etc.
Fencing and Gates
Roads, Paving, etc.
Covered Parking, Walkways, etc.
Pergolas, Canopies, etc.
Minor Construction Work
Pools, etc.
Sports Facilities
Garden Works
Miscellaneous Items
‫܀‬
Training
Training
Preliminaries
Preliminaries
Contractor's Fee
Contractor's Fee
Contingency allowancesPrice and Detail Development
Building Contract Contingencies
Escalation
Pre-tender escalation
Contract escalation
Value Added Tax
Value Added Tax
Problems encountered in applying this system
Let us consider some of the problems encountered in applying this system
of estimating in a quantity surveyor's office:
Pricing
At component level it is fairly easy to price items and many item prices
can be built up from rates obtained from bills of quantities. At element
level this is more difficult and it is usually necessary to employ cost
information obtained by analyses of previous projects.
Unit of measurement
In which unit of measurement should an element or a component be
measured? In the case of a wall, for example, it is obvious that the best
unit of measurement is per square metre on elevation.
Consider however, rain-water pipes:
Linear would be too tedious.
Roof area is not consistent enough, since a high building and a low
building with the same roof area but with a considerable difference
in the length of rain-water pipes would have the same unit of
measurement.
To overcome these problems, the "construction area” as defined
under "General" above is used.
Consider as a further example the unit to be used for built-in cupboards.
Originally area on plan, cubic content, length on plan and area on
elevation were investigated and it was found that in most cases area on
elevation was most consistent and therefore most acceptable. Another
method that has gained ground is to measure cupboards per door.
Measurement required
In any estimating system it is necessary to define exactly the method of
measurement as also the degree of accuracy required. It should be borne
in mind that if the measurements required are too detailed or complicated
then your are in fact back to the ultimate estimate, which is the bills of
quantities. An estimating system should be both fairly accurate and
capable of providing an answer over a reasonably short working period.
In view of the above certain measuring conventions have been adopted.
Flooring for instance is measured right across internal and external walls,
external facade right across the concrete floor slabs but internal walling
from top of slab to underside of slab. In the case of floor finishes and
the external facade there will of course be a certain overmeasure which
has to be allowed for in either the pricing or by deducting a percentage.
Build-up of prices at component level
As mentioned earlier, it is fairly easy to build up prices at component level.
The following example illustrates the point:
Component: Solid floor finish (price per m2)
Screed
Vinyl floor finish
Less: Adjustment for overmeasure (as explained above) 10%
Plus: Sundries (e. g. floor finish in openings, brass dividing
strips, etc.) 2%
Preliminaries 12%
Rate per m2
R13,00
R38.00
R51,00
(R 5,10)
R45,90
R 0.92
R46,82
R 5,62
R52,44
Build-up of rates at element level
At element level it is more difficult to build up a rate.
The following are illustrations of what is involved in building up an element
rate. It has been assumed for the purpose of these examples that the
individual component rates have already been built up or obtained from cost
research and are complete with the relevant preliminaries, etc. added:
External walling (total area of element taken as 1 000 m2 on
elevation)
Walling600 m2 at R 90,00 R 54 000,00
External finishings600 m2 at R 40,00 R 24 000,00
Windows400 m2 at R180,00 R 72 000,00
Window sundries (glass, etc.) 400 m2 at R 95,00 R 38 000,00
External doors18 at R500,00 R 9 000,00R197 000,00
Element unit rate is therefore R197,00 per m2 on elevation (1 000 m2).
Electrical installation
Usually this is inserted in the bills of quantities as a lump sum figure.
The only way of determining a rate for this element is by cost research
into past tenders, or by obtaining a rate from the electrical consultant.
For simple installations, such as houses it is possible to estimate an
amount for the basic switchgear, earth leakage, etc. (say R2 000,00);
then add light and power points at say R120,00 per point; stove and
geyser isolators at say R180,00 each; bells, TV-points and telephone
points at R90,00 each and cable at say R30,00 per m.
Plumbing
Plumbing points such as water supplies, waste disposal, etc., are
priced by cost research into past tenders.
The following is an example of an elemental estimate at component
level for the element “Plumbing":
DIMENSIONS
15
3/15
2/15
15
45
30
DESCRIPTION
WC
WHB
Baths
Sanitary fittings sundries
Sanitary plumbing
Cold water supply
Hot water supply
Geysers
Cold water supply
QUANTITY
15
15
15
45
45
45
30
15
15
UNIT
No
No
No
No
No
No
No
No
No
TOTAL ESTIMATED COST OF ELEMENT: PLUMBING
RATE
R 650,00
R 360,00
R 1 150,00
R 150,00
R 600,00
R 550,00
R 380,00
R 2 400,00
R 550,00
AMOUNT
R 9 750,00
R 5 400,00
R 17 250,00
R6750,00
R 27 000,00
R 24 750,00
R 11 400,00
R 36 000,00
R 8 250,00
R146 550,00
(The above is equivalent to an average rate of R2 442,50 per "point" – 60
points.)
Use of elemental system at various stages of design
The use of the elemental system of estimating at the various stages of the
development of a design can be illustrated as follows:
At diagrammatic sketch plan stage. Use the element rate, as no detail
for estimating at component level will be available.
At stages when full-sketch plans are available. Use component rates.
At working-drawing stage. Use component rates, but for increased
accuracy, actual tenders may be substituted for components, or
alternatively, a check on the cost of any component could be made byactually taking off the quantities
and pricing that component.
It is apparent therefore that the elemental system of estimating can be applied
with an ever-increasing degree of accuracy as more detailed drawings and
more facts become available. Unlike other systems it is also possible to do
an accurate post-mortem analysis at component level to see where mistakes
have been made or where inaccuracies have occurred, thus enabling the
estimator to improve his techniques.
Inherent problems
It is not suggested that the elemental system of estimating has no inherent
problems.
Three of the most obvious of these problems are listed below:
If any item is overlooked by either the architect (not indicating something
on the drawings) or the quantity Surveyor, then this is fatal. If a fitting,
for example, is not indicated on the drawings and is not assumed or
measured by the quantity Surveyor, then such fitting will just not be
included in the estimate.
To overcome this problem to a certain extent a percentage for "price
and design development" is added to the estimate, which percentage
varies according to the stage of development of the drawings at time of
estimating.
It is necessary to assume specification and/or detail at an early stage
when these may not yet have been considered by the architect. To a
certain extent, this is a blessing in disguise, for it is much better to be
able to indicate specifically what has been allowed in an estimate of
cost rather than to be vague, as is inherent in many other systems of
estimating. It is also necessary to remember that a calculated guess is
better than nothing at all.
It takes longer to prepare an elemental estimate than for instance an
estimate prepared on the square-metre system.
10.2.7 General
‫܀‬
The architect's role
Without the co-operation of the architect, cost planning and control cannot
function. Most architects however do appreciate the importance of economics
in the development of building projects.
Again, it should be emphasised that the purpose of cost planning and
control is not to produce the cheapest possible building by the selection of
the cheapest specification, but to help the architect to achieve a balanced
design within a given budget.
To assist the quantity Surveyor, the architect should:
Allow the quantity Surveyor sufficient time to prepare the estimate of
building costs and/or a feasibility study.
Inform the quantity Surveyor of all changes in design or specification
and call for new estimates from time to time as the drawings progress.
Provide the quantity Surveyor with all the details that he requires for the
preparation or an elemental estimate. The architect is in a better position
than the quantity Surveyor to make the necessary assumptions on design
and specification.
Contract price indices
Due to continuous inflationary escalation in the cost of labour, building
materials and other resource inputs, a contract price index is vital for updating
past records for estimating purposes.
At present there are two bodies that provide the building industry with contract
price indices together with other relevant statistics on a continuous basis,
namely:
Bureau for Economic Research - University of Stellenbosch
This Bureau publishes two quarterly publications namely “BUILDING
AND CONSTRUCTION" and "TRENDS IN BUILDING COSTS”.
The first of these is distributed to firms who pay a certain annual
subscription fee whilst the second publication is distributed free of charge
to all participating quantity surveying firms. By "participating" it is meant
that bills of quantities are analysed and the information thus obtained is
filled in on a standard form provided by the Bureau.
Central Statistical Service: Contract price index for buildings
A monthly index that is distributed to all quantity surveying firms and all
firms are required to provide information to the Department on its
prescribed standard forms on a continuous basis.
Accuracy of estimates of building costs
An estimate of building costs based on working drawings and which is within
five per cent of the actual tender amount, after allowance for the "cost effect
of time", is considered accurate. Those within ten per cent of the actual
tender amount are deemed to be fairly accurate,
10.2.8 Estimating total capital outlay (TCO) on a project
It is common practice to capitalise all costs attributable to a project from the day
of inception up to a certain date, usually the date on which the facility is occupied
by the user and starts its operating or income-producing life. Property development
or building projects are usually completed over a certain length of time and most
costs are expended on a periodic basis.
It is fairly easy for the estimator to grasp that major “capital” outlays such as
purchase price and other costs of land, building cost and professional fees form
a part of total capital outlay. What is sometimes less obviously part of TCO and
therefore often overlooked are cost items which are usually, during the operating
phase, a running cost against revenue such as for example municipal rates and
taxes, interim finance charges (interest on building loan, etc.) and the like.
Estimators then either ignore these costs or hope that in some vague way they
will be accounted for in the general overhead cost of the organisation.
TYPICAL COST ELEMENTS (INITIAL CAPITAL OUTLAY) OF A BUILDING OR DEVELOPMENT PROJECT
LAND DEVELOPMENT COST
OTHER "ADD-ON"COSTS
PROFIT
BUILDING COSTBuilding cost
* Professionalfees
CONTRIBUTION TO
ORGANISATIONAL/INSTITUTIONAL
OVERHEADS OF
OPERATIONAL COSTS
General
"head office"
overhead
Purchase price of land (including agent's commission)Transfer duties and conveyancing fees
* Installation of services: construction and professionalfees
* Distribution to owners/
shareholders as return
on capital and reward
for risk and effort
* Legal
* Financial
(FEES ARE PARTLYOPTIONAL)
* Otheradministrative
* Fees and contributions to local and other authoritiesInvolved
(OPTIONAL)
Specific charges to
the project
(PARTLY OPTIONAL)
(SOME OF THE ABOVE OPTIONAL DEPENDINGON HOW LAND IS ACQUIRED)
BUILDING COST BREAKDOWN
total capital outlay (TCO)
Figure 10.4 Typical setting out of total building project costs or
Typical cost elements in building or development projects are shown in figure 10.4.
"ON-SITE" COSTS TO CONTRACTOR
"OFF-SITE" COSTS
TO CONTRACTOR
CONTRACTOR'SPROFIT
GENERAL "HEADOFFICE" OVERHEAD
PERMANENT STRUCTURE(DIRECT COSTS)
Materlals
Components andfixtures
* Labour used ininstallation
* Office rent
TEMPORARY
CONSTRUCTION
SUPPORT SYSTEM
(INDIRECT COSTS)
Contract and site
management and
administration(including supervision)
* Temporary facilitiesand sevices
* Temporary works
* General contractualobligations
PROFESSIONAL FEES
(PARTLY OPTIONAL)
* Land surveyorTown planner/urbandesigner
* ArchitectQuantity Surveyor
* Consulting engineer(s): Geotechnical
Civil/structural
Electrical
Mechanical
* Service levies
* Administrative salariesand expenses
* Telephone and postage
* Furniture and equipment
10.3 ESTIMATING TOTAL COST OF A BUILDING ORFACILITY IN USE OVER ITS LIFETIME
10.3.1 Lives of buildings
It is not always easy to predict or assess the probable physical life of a building/
facility or any of its components. Buildings are constructed to different standards
and subject to varying standards of maintenance.
"It is also possible to distinguish between 'structural life' and 'economic life'.
Structural or physical life is the period which expires when it ceases to be an
economic proposition to maintain the building, while economic life is concerned
with earning power and is that period of effective life before replacement;
replacement taking place when it will increase income absolutely. It is probable
that optimum life is determined primarily by the earning power of the building, and
secondarily by the structural durability.
Changing social and economic conditions can have a considerable influence on
the life of a building which can become ill-suited to present-day needs and its
demise may also be accelerated by the significant ratio of land to building costs.
Wherever possible, the aim should be to extend the economic life of a building
by making the structure adaptable and by careful management and control of
the surroundings. Hence the actual physical life of a building is frequently much
greater than its economical life, but the building is often demolished before its
physical life has expired in order to permit a more profitable use of the site, or
because it is found cheaper to clear and rebuild than to adapt the building to the
changed requirements" (Seeley, 1987:18).
10.3.2 Life-cycle costing
Life-cycle costing is an analytical technique for the comparative evaluation of
time-phased costs and revenues attributable to a project or an asset or component
over a specific planning period.
The total life-cycle cost of an asset (or component) is defined as the total cost of
that asset over its operating life, including initial acquisition costs and subsequent
running costs.
Life-cycle costing is also known as costs-in-use, engineering economics, cost
benefit study and terotechnology. Irrespective of the name, it is a tool to be used
in the decision-making process, the objective being to ensure the best value for
money over the economic lifespan of the asset, with the time value of money
taken into account.
10.3.3 Relationship of capital, maintenance and running costs
It is important to building owners that a building is designed in such a way that it
secures a reasonable balance between initial and future costs.
Initial costs
Land
Construction
Professional fees
Total costs
(life span of building)
Running costsMaintenance
Operating services
(operating and cleaning)Energy
User costs
Occupational charges
Rates
Insurance
Modifications
and alterations
Estate control
(management
Figure 10.5 Breakdown of total costs of a building in use overits lifetime (Seeley, 1987:24)
10.3.4 Difficulties in assessing total costs
“There are a number of problems in endeavouring to assess total costs or costs
in use at the design stage, and the more important ones are now listed. It is difficult to assess the
probable maintenance costs of different materials,
processes and systems. There is a great scarcity of reliable maintenance
cost data tabulated in a meaningful way. It is not easy to predict the lives of
materials and components in a variety of situations. Even the lives of
commonly used materials like paint show surprising variations and are
influenced by a whole range of factors, including type of paint, number of
coats, condition of base, extent of preparation, method of application, degree
of exposure and atmospheric conditions.
There are three types of payment involved: initial, annual and periodic. All
three have to be related to a common basis for comparison purposes, and
this requires a knowledge of discounted cash flow techniques.
The selection of a suitable long-term interest rate is difficult; rates rose
dramatically in the 1970s and fluctuated widely in the 1980s.
Inflationary trends may not affect all costs in a uniform manner, thus distorting
significantly the results of costs in use calculations.
BUILDING PRACTICE – VOLUME 2
Where the initial funds available to a building owner are severely restricted, it
is of little consequence telling him that he can save large sums in the future
by spending more on the initial construction” (Seeley, 1987:24, 25).
10.4 COST BUDGETING
Cost budgeting involves allocating the overall cost estimates to individual work
items in order to establish a cost baseline for measuring project performance.
Cost budgeting usually also includes cash-flow projections in order to enable the
planning and monitoring of expenditures over time.
Inputs
1. Cost estimates
2. Project schedule
Tools and techniques
1. Cost estimatingtools and
techniques
Outputs
1. Cost performancebaseline
Figure 10.6 Cost budgeting process (A guide to the Project ManagementBody of Knowledge, 1996:78)
10.5 COST CONTROL
Cost control is concerned with (a) influencing the factors which create changes
to the cost baseline to ensure that changes are beneficial, (b) determining that
the cost baseline has changes, and (c) managing the actual changes when and
as they occur.
Cost control includes:
monitoring cost performance to detect variances from plan.
ensuring that all appropriate changes are recorded accurately in the cost
baseline.
preventing incorrect, inappropriate, or unauthorised changes from being
included in the cost baseline. informing appropriate stakeholders of authorised changes.
Cost control includes searching out the "whys” of both positive and negative
variances. It must be thoroughly integrated with the other control processes
(schedule control, quality control, etc.). For example, inappropriate responses to
cost variances can cause quality or schedule problems or produce an unacceptable
level of risk later in the project.
Inputs
1. Cost baseline
2. Performance reports
3. Change requests(variations)
4. Cost managementplan (including
cash-flow projections)
Tools and techniques
1. Cost changecontrol system
2. Performancemeasurement
3. Additional planning
4. Computerised tools
Outputs
1. Revised costestimates
2. Budget updates
3. Corrective action
4. Estimate atcompletion
5. Lessons learned
Figure 10.7 Cost control process (A guide to the Project ManagementBody of Knowledge, 1996:80)
A building contract price (based on accepted tender) may change during the
course of the contract due to any of the following and other factors: Remeasurement on site of
provisionally measured quantities.
Changes in design and/or specification ("variation orders”).
Adjustment of provisional sums and prime cost amounts ("PC amounts”).
Delays and extensions of time due to change in scope of work, lack of
information, etc.
Omission of allowances for contingencies. Fluctuations in the cost of labour, materials, etc. ("Contract
Price Adjustments”).
On a building project the instruments/processes involved in cost control generally
include cost estimates/plans, budgets, cash flow projections, tender and contract
documents (including bills of quantities where available), progress payment
certificates including contract price adjustments due to escalation of labour,
material and other costs, pricing of variations, remeasurements and other
adjustments, cost reports and final accounts. The final account is a document,
usually prepared by the quantity surveyor, which sets out in detail, and then
summarises all legitimate and accepted changes that occurred to the original
contract price during the course of the contract.
10.6 CONTRACT PRICE ADJUSTMENTS
10.6.1 Introduction
In the past, it was customary not to make allowances for claims from the
contractor for fluctuations in labour costs and material. Mainly on account of the
tremendous fluctuations of the costs of labour and material in the past few
decades, contractors in general have arrived at the conclusion that the risks that
they take are not in proportion to the profits that can be made and, via the Building
Industries Federation South Africa (BIFSA), have insisted on compensation for
the escalation in building costs.
There are mainly three methods by which escalation in building costs can be
handled, namely:
Fixed price
Proven costs
Contract Price Adjustment Provisions (CPAP) of the Joint Building Contracts
Committee (JBCC), known up to 1995 as the BIAC (Haylett) formula
10.6.2 Fixed price contracts
A fixed price contract is one where the contractor accepts full responsibility for any
fluctuation in the costs of labour and material. The employer will not, therefore,
reimburse the contractor for any fluctuations in building costs after acceptance of a
tender, and the contractor must allow in his tender for any expected fluctuations.
Members of the Building Industries Federation South Africa generally do not accept
fixed price contracts under tender conditions, unless the contract amount does not
exceed R500 000.
Fixed price contracts can, however, be arranged with a single contractor, but the
employer must bear in mind that if the building period is prolonged (i. e. longer than
12 months), the risks for the contractor are extremely great, which can naturally
lead to the contract price being abnormally high.
The advantage for the employer, in the acceptance of the fixed price method of
contract price adjustment, is that his ultimate risk of escalation in building costs is
considerably reduced.
10.6.3 Proven costs contracts
In this type of building contract, the contractor sets his price according to the
labour and materials costs prevailing at the time of tendering. Any increase or
decrease in the tariffs, by comparison with actual labour and material costs when
they were acquired for the contract, is for the employer's account.
The Building Industries Advisory Council (BIAC) published a standard “proven
costs” contract price adjustment provision many years ago. This document is no
longer recognised by the Building Industries Federation South Africa (BIFSA), and
although the South African Property Owners Association (SAPOA) has published a
revised form thereof, no agreement could be reached between the two bodies
regarding the final wording of the stipulations.
The proven costs method is seldom used and, if used, it is usually in negotiated
contracts. It can be advantageous to the employer to use proven costs methods
in the adjustment of the contract price, if there is a possibility that other methods of
contract price adjustment can result in an overcompensation for the contractor.
‫܀‬
10.6.4 Contract Price Adjustment Provisions of the JBCC[formerly known as the BIAC (Haylett) formula]
Introduction
A manual and referance guide for practical application of the formula is
published by and available from the Joint Building Contracts Committee
(JBCC), with revisions and interpretations issued from time to time.
Students are advised to obtain a copy of this manual, and to continually
keep themselves up to date with possible revisions and interpretations.
The following is an excerpt from the manual which explains how the
provisions work:
"How the provisions work
The CPAP provides for the adjustment of contracts in respect of: General and industrialised building
work
Subcontract work carried out by nominated, selected and nonnominated subcontractors
Direct contract work comprising specialist and engineering
installations related to building projects
Standard composite indices have been compiled in consultation with
CSS to include the weighted labour, material and plant components
applicable to a number of defined work groups. CSS in Statistical
Release PO151 publishes these composite indices each month.
In brief the CPAP operates as follows:
A number of work groups are defined into which the work
contained in a building contract can be subdivided
CSS publishes a like number of sub-indices, reflecting price
movements of labour, material and plant content of each work
group
The principle agent values the work executed for certificate
purposes in the normal way but in addition he allocates the value
of the work to the respective work groups
In a particular month the value of work certified in each work
group is adjusted in relation to the movement in the index value
for the applicable month compared with the index applicable to the
tender date. This is done so that the work executed in a particular
period is adjusted in relation to the index value for approximately
the same period
The work groups have been restricted to a practical number to limit
and simplify the work required at the time of certification.
The approach adopted is that certain materials lend themselves to
grouping for costing purposes and consequently reference is made to
'work group' rather than "trade" as is customary in documentation in
the building industry. For example, steel windows, steel door frames
and suspended steel ceilings are assembled to limit the number of
groups, as the materials originate from the same basic source and the
percentage fluctuations in labour costs are likely to be similar.
Calculation of adjustment
The principle agent shall calculate an amount of adjustment for each
valuation period in respect of each work group by the application of
the formula:
Where: A=
0,85
V
Xe
Χο
A= 0,85 V
Xe
Хо
the amount of adjustment
a constant which provides for a 15% non-adjustable
element
the work value for adjustment in such work group
and the valuation period
the value of the index applicable to such work group
and the valuation period which shall be the value for:
(a) The month before that during which the progresscertificate is dated in respect of certificatesissued
up to and including the 15th of the month
(b) The month during which the progress certificateis dated in respect of certificates issued after the
15th of the month
the value of the index applicable to such work
group for the base month
The amount of adjustment calculated in terms of the above shall be:
Shown seperately in a statement supporting any payment
certificate issued according to the relevant agreement
The net amount to be added to or deducted from the contract
value
In respect of work carried out by nominated, selected or any other
subcontractors. This shall be irrespective of whether or not the
agreement provides for a cash discount to the contractor in
respect of any amounts due. Payment to such subcontractors
shall not be subject to any such discount
Subject to the same conditions in respect of retention, any other
form of security or any other monies due to or from the contractor
in terms of the agreement"
QUESTIONS FOR SELF-EVALUATION
1.
2.
Discuss the difference between cost estimating and pricing of
building work with regard to:
(a) Building contractors
(b) Building employers (clients)
List 5 types of buildings for which the unit-cost method of
estimating would be suitable to set initial cost norms and
parameters and briefly motivate why these are considered
suitable.
REFERENCES
Joint Building Contracts Committee. 1998. Contract Price AdjustmentProvisions. Manual and reference
guide.
(10)
(10)
20
Project Management Institute. 1996. A guide to the Project Management Bodyof Knowledge. USA.
Seeley, I. H. 1987. Building Maintenance. 2nd edition. Southampton: Macmillan.
The Association of South African Quantity Surveyors. 1998. Guide to Elementalost, Estimating and
Analysis for Building Works.
NOTES
PROCUREMENT FOR
BUILDING PROJECTS
CONTENTS
LEARNING OBJECTIVES
11.1
11.2
11.2.1
11.3
11.4
11.4.1
11.4.2
11.4.3
11.4.4
11.5
11.5.1
11.5.2
11.5.3
11.6
11.7
11.7.1
11.7.2
11.7.3
11.7.4.
INTRODUCTION
Introduction
TENDERING
METHODS OF OBTAINING TENDERS
Competitive tendering
Negotiated tenders
Two stage tenders and consecutive tenders
Tender evaluation and contract award
SPECIFICATION, MEASUREMENT AND PRICING FOR
TENDERING PURPOSES
11
Specification
Measurement of building quantities
Estimating and pricing by contractors for tendering purposes
CONTRACT ADMINISTRATION
RESEARCH, STANDARDS AND TECHNICAL EVALUATION OF
BUILDING MATERIALS AND METHODS (SABS,
CSIR, AGRÉMENT, NHBRC)
The South African Bureau of Standards (SABS).
The Council for Scientific and Industrial Research (CSIR) –
Building Technology Division (BOUTEK)
The Agrément system for technical evaluation of building
materials and methods in South Africa
The National Home Builders Registration Council (NHBRC)
PAGE
135
135
135
135
136
137
137
139
141
142
142
142
149
156
162
162
162
164
164
165
11.8
11.8.1
11.8.2
11.9
11.9.1
11.9.2
11.10
11.10.1
11.10.2
11.11
BUILDING REGULATIONS
The National Building Regulations
Application of the National Building Regulations
GENERAL STATUTORY REQUIREMENTS AND THE ROLE
OF LOCAL AUTHORITIES IN BUILDING AND DEVELOPMENT
PROJECTS
General statutory requirements impacting on land development
and building work
The role of local authorities
THE ROLE OF THE CLERK OF WORKS AND THE RESIDENT
ENGINEER
The clerk of works (COW)
The resident engineer
THE ROLE AND OPERATIONS OF THE BUILDING
CONTRACTOR
11.11.1 Introduction
11.11.2 Planning and organisation
11.11.3 Quality control
11.11.4 Financial control and cash flow
11.11.5 Estimation and preparation of tenders
11.11.6 Contractor's pre-construction activities
11.11.7 Project site meetings
11.11.8 Contractor's own site meetings
11.11.9 Completion
11.11.10 On-site process: Some aspects to consider
QUESTIONS FOR SELF-EVALUATION
REFERENCES
165
165
166
167
167
170
172
172
175
175
175
175
177
178
178
179
180
181
182
182
185
LEARNING OBJECTIVES
The objective is to provide the student with an overview of the processes
involved and factors playing a role in procurement of building contracts up to
conclusion of the building process.
11.1 INTRODUCTION
Procurement includes the processes required to acquire goods and services
from outside the organisation requiring such goods and services (in our case, a
completed building or buildings for the employer or client). Procurement usually
involves the following major processes: Procurement planning: determining what to procure and when.
Solicitation planning: documenting product requirements and identifying
potential sources (design, specification, tender documents).
Solicitation: obtaining quotations, bids, offers, or proposals as appropriate.
Source selection: adjudicating tenders and selecting a contractor.
Contract administration: managing the relationship with the seller
(contractor).
Contract close-out: completion and settlement of the contract (including
Final Account).
‫܀‬
11.2 PROCUREMENT FOR BUILDING PROJECTS
11.2.1 Introduction
This procureincnt process for building work can be summarised as
follows:
Tendering
Negotiation
Selling on open market
The foliowing types of iondsrs ars generally used: Tenders by open invitation
Restricted tenders by
() selective invitation
(ii) pre-qualification by set criteria
Negotiation with one or more contractors
D
The tendering procedure is as follows: Prepare tender documentation
Advertise or invite (including compiling list of tenders)
Closing of tenders
Adjudication of tender and recommendation to client
Acceptance of tenders and appointment of contractor
Signing of contract
11.3 TENDERING
The term "tender" can be defined as follows:
"Tendering is a science and an art. The science is the logical compilation of a
series of factors such as labour, materials and plant into a recognised order and
with such items as output of labour based on historic information. The art of
tendering is the judgement on finance, overheads and profit usually exercised by
the principals of the firm tendering."
The contractor in submitting a tender makes an offer to complete a building, based
on the Agreement and Schedule of Conditions of Contract as contained in the
tender documents. If the client accepts the offer a contract is formed that bind
both parties.
The purpose of a tendering system is the establishment of a process of
procurement which is fair to the client, the tenderer and the professional
consultants.
The client
The client normally desires the following end results from a tendering
system:
the lowest price
the shortest construction time
the best possible quality
The tenderer
The tenderer usually expects the following of a tendering system: to be in competition with other
contracting firms of the same kind
(financially, technically and administratively);
that all tenderers are allowed equal time to tender, that the basis of the
tender is uniform to all and that they will be subject to the same criteria
of evaluation.
The professional consultants
The professional consultants strive to achieve through a tender system the
following:
an honest approach from the contractor to complete the work that
she tendered for in a proper manner;
reasonable assurance that the contractor is financially, technically and
administratively able to complete the work.
11.4 METHODS OF OBTAINING TENDERS
or
After the type of building contract has been chosen for the project, attention
shifts to selection of the contractor. The client can simply be advised to go to
the nearest or a well-known contractor for a price. Such an attitude will however
not satisfy the client's need to obtain the best price. The most effective answer
is to call for tenders on a competitive basis. If the project under question is of
such a nature that specialist services are needed which can be provided by one
firm only, it will serve no purpose to consider competitive tenders. Negotiations
with that particular firm is then the answer.
There are thus two basic methods of obtaining tenders namely competitive
tenders and negotiated tenders.
Selection through competitive tendering is usually more acceptable to clients and
the professional team than negotiated tendering.
However, in advising the employers on the method to be employed in obtaining
tenders the architect and quantity Surveyor should take due cognisance of the
state of market, the nature of the work, the time available for documentation and
any other pertinent factors.
'11.4,1 Competitive tendering
Competitive tendering is used on most projects, mainly to obtain the best
possible price. An advanced level of detail design is required as against that for
negotiated tenders, but it is in any case in the interest of both parties to have as
much information as possible available during tender stage. Cost-plus building
contracts need much less detail design information at tendering stage but have
notable risks and disadvantages.
The aim of the tenderer is not just to obtain the work, but rather to obtain it at a
price that will enable him or her to complete the work thoroughly, on time and at
a reasonable profit. The competition between tenderers can be fierce at times
when building work is scarce and tenderers will apply every means at their
disposal to gain an advantage over their rivals.
A problem often encountered is the question of whether to test the whole market
on open invitation or whether tenderers should be pre-selected.
Both options are discussed briefly below:
Open tenders
With this method the whole market is tested and it is especially the public
sector that gives preference to this method of tendering. To obtain bona fide
tenders a deposit is normally required when issuing the tender documents.
The tender is usually advertised in the press and qualified in the sense that
the employer does not bind himself to accept the lowest or any tender.
The advantage of calling for open tenders is that the whole of the market,
including suppliers, specialists, subcontractors and contractors, are aware of
the fact that a substantial number of contractors are competing for the tender.
Depending on the current market conditions, this could result in keen tenders
being obtained. The disadvantage is that a contractor who is not suitable for
that specific contract, may be the lowest tenderer and the employer may be
tempted to accept such a tender.
This method therefore, requires careful evaluation of the tenderers, not only
to make sure that the tender in itself is acceptable but also to make sure that
the tenderer is technically and financially capable of completing the work.
Tendering costs money and this cost is carried forward to the client's account
in the long run. If fifty tenderers are allowed to tender, forty nine of them will
have considerable expenses that cannot be directly recovered. Each firm
must therefore carry forward the cost of its unsuccessful tenders to those
that are successful.
Selected or restricted tenders
Selected tenders are obtained by calling for tenders from a list of contractors
pre-selected for the specific contract on the basis of financial stability, previous
experience, specific exp se in a particular field of construction or quality of
workmanship, or a combination of these factors. It should be noted that the
employer has a moral obligation to accept the lowest tender. The advantage
is that each contractor should be capable of carrying out the contract. The
disadvantage is that the number of tenders is limited, and as such the
competitive element is reduced.
This could lead to ring-forming, where a group of contractors colludes in
deciding who shall submit the lowest tender, with the other members of the
ring submitting cover prices. Each of the members of the ring takes it in turn
to be the lowest tenderer on successive jobs. In this way the successful
tenderer in each case obtains a contract at an inflated price.
Selection can be done in two main ways:
(i) By invitation
(ii) By pre-qualification through a set of criteria
Generally, when calling for competitive tenders, the following should be
borne in mind: Time for tendering is limited, the tender period usually being three
to six weeks, depending on the nature and size of the building.
Time for site and progress planning is limited.
Only once a tender has been accepted will the employer know
what subcontractors the main contractor proposes to use.
The employer is limited by Master Builders' Associations
regulations to lump-sum and quantities forms of contract.
11.4.2 Negotiated tenders
Although selection by competitive tendering is generally more acceptable, there
are occasions when it may be in the interest of the employer to negotiate a tender,
for example: When the competitive element has temporarily disappeared from the building
market because of an over-abundance of work.
When the contract is of a particularly difficult type, or requires specific expertise
or plant, and it is obvious that only certain contractors specialising in the type
of work required should even attempt the execution of the project.
When it is known that whatever the outcome of competitive tenders, the
contract will nevertheless be awarded to a specific contractor for specific
reasons, such as the contractor's company being affiliated to that of the
employer.
When it is in the interest of the employer to use Package, Turn-key or
Managed forms of contract.
When negotiating a tender, the foilowing aspects are of importance: Negotiations should be based upon
as complete a set of documentation
as possible, and should be conducted on behalf of the employer by a
person well versed in building costs, contract conditions, etc. Usually
the employer is represented by a quantity Surveyor and negotiations
are based on full bills of quantities.
BUILDING PRACTICE
VOLUME 2
When commencing negotiations with a contractor, it is necessary to
establish whether agreement can be reached concerning costs of certain
basic items, e. g.: Mark-up to cover profit and overheads on own work, work performed
by ordinary subcontractors and work performed by selected
subcontractors.
Attendance on work performed by ordinary subcontractors and by
selected subcontractors.
Detailed pricing of the “Preliminaries” items.
Detailed build-up of hourly rates for artisans and for semi-skilled
and unskilled labourers.
Certain performance indicators such as the number of bricks a
bricklayer will lay per day on average for say half-brick walls and
one-brick walls on the specific contract, the average rate at which
reinforced concrete in bases will be cast, etc.
It is also necessary to establish with the contractor a list of work to be
performed by ordinary and by selected subcontractors respectively for
which competitive tenders will be called.
Many contractors feel that they can make a contribution at an early stage
of the project. Contractors also point out that in many cases their own
work (mainly confined to "Preliminaries” work and concrete and brickwork)
totals between 30% and 35% of the whole contract amount and that
subcontractors account for the rest.
It is generally accepted that it is in the contractor's best interest if he or she can
persuade the employer to negotiate only with him or her. There is, however, no
conclusive evidence that it is always in the best interests of the employer, as a
doubt always exists as to whether competitive tenders would not have produced
a reduction in the overall cost to the employer.
Sometimes contractors also use initial negotiations to strengthen their position to
such an extent that it is virtually impossible not to continue with them, even if the
employers may have second thoughts about negotiated tenders.
The argument, sometimes put forward by contractors and in many cases accepted
by employers, that contractors have a specific contribution to make in the early
design stage has little validity if the architect and the professional team are well
experienced and perform their duties properly. Some contractors do manage to
persuade the employers to accept their contribution at an early stage and then
use this early introduction to so strengthen their position that the professional
team find that they have virtually no negotiating power left. By emphasising the
point that “Time is the essence of the Contract (and in many cases it actually is),
some contractors move onto the site before negotiations are completed, and again
the professional team find their negotiating power eroded.
The point is sometimes raised that a lot of specialised manpower is wasted in the
preparation of tenders and that all contracts should be negotiated for this reason
alone.
This is perfectly true for many engineering contracts where the documentation is
insufficient to enable the contractor to estimate cost accurately without having to
prepare further drawings, bills of quantities, etc., itself. This argument is not
generally valid for the building industry, as the fruitless expenditure in tendering
on complete documentation is negligible in relation to the tumover of the industry.
Civil engineers should seriously consider employing professional quantity Surveyors
to assist them in providing the contractor with comprehensive tender documents.
It is perfectly true that sound contractors are often undercut in competitive
tendering by inexperienced and reckless newcomers who frequently find that they
have miscalculated to the extent that they eventually wind up in the insolvency
court. This is not in the best interests of the industry. The remedy does not
necessarily lie in negotiated contracts, but possibly with education and training
and also possibly with pre-selection of tenderers.
It is generally accepted that negotiated tenders usually result in contract amounts
which are from 4 to 6% higher than comparable open tenders attained under
competitive conditions.
Contractors point out, however, that a negotiated contract with a pre-selected
reputable firm of contractors may very well result in a substantial reduction in the
contract period.
11.4.3 Two stage tenders and consecutive tenders
Two stage tenders and consecutive tenders are variations of both competitive
tenders and negotiated tenders.
A two stage tender is when the contractor is selected early in the design process
by means of a competitive tender. His or her tender is thus based on less
information than will be found with normal competitive tenders. The contractor
then works with the professional team as the design and planning of the project
develops and his or her final tender is then based on the information given at
the time of his or her original tender.
Consecutive tendering makes provision for a number of circumstances, for
instance, where the client offers to the contractor consecutive phases of the project,
subject to satisfactory períormance and retendered or renegotiated prices.
(D
11.4.4 Tender evaluation and contract award
Evaluation of tenders (and tenderers) before awarding the contract, is a crucial
step in ensuring successful completion of projects.
Tenders are usually checked for large errors which may influence the contractor's
ability to carry out the work for the price tendered, even distribution of rates
(front-end loading, padding of rates for work where possible extras are anticipated,
etc.).
Tenderers are usually investigated in terms of financial stability, capacity to do
the work (plant, skilled personnel, organisational strength) and track record
(references from previous employers, consultants, etc.).
Contracts are usually signed only when the contractor has met certain conditions,
e. g. providing performance guarantees, proof of insurances, priced bills of
quantities (or other cost breakdowns) and a programme for the execution of the
work.
11.5 SPECIFICATION, MEASUREMENT AND PRICINGFOR TENDERING PURPOSES
11.5.1 Specification
Whai is a specification?
One dictionary definition of specification reads: "... details, instructions, etc.
for the design and making of something".
In the case of building projects, the specification is a comprehensive and
detailed description of the type and quality of materials and components to
be used, and the standards of workmanship required. It is a communication
tool between the parties involved, and supplements the architect's or
engineer's drawings with information which cannot be clearly or easily shown
on the drawings. Sometimes, on smaller projects or often in the case of
repair/renovations and maintenance contracts, there are no drawings and
the specification serves as the only description of the work to be done.
Specifications can be contained in:
(a) annotation (notes) on drawings and schedules
(b) supplementary notes and item descriptions in bills of quantities
(C) separate documents
Purpose and use of specifications
The specification is in the first instance a communication tool between the
parties involved on a building project.
It is read by:
the employer or client to know what kind of building to expect,
the builder's estimator as information on which to base a competitive
tender,
the quantity Surveyor to enable him to prepare bills of quantities as a
basis for competitive tendering and
the clerk of works and/or contractor's foreman during execution of the
works as architect's instructions to carry out the work and basis for
inspection and quality control.
Principles of specificazion writing
The essentials for writing good specifications: Know what you want.
(This requires knowledge of building science and practice, and careful
thought)
Express it clearly and concisely.
(Use plain language and make sure words have the same meaningthroughout.)
A specification is a document for quick reference and understanding. It
should be brief and to the point, and should make optimum use of available
standards and codes of practice (such as SABS, etc.).
A specification, when accompanied by drawings, should explain the purpose
and intent of the drawings more fully and clearly, and should not repeat or
contradict information given on the drawings.
It should be arranged in short paragraphs with clear headings in systematic
order. The order can be based on:
the trades in the bills of quantities
(e. g. groundworks; concrete, formwork and reinforcement; masonry,
etc.)
building activities or operations
(e. g. founciations; surface beds; walls; roofs, etc.)
Principles of good communicationMessage must be suitable for the receiver,
Arrange contents to read from the general to the particular.
Be clear and concise - avoid repetition.
Keep the information together – avoid cross referencing.
Guidelines for good specification writing
Know your materials and building practice.
Know local conditions and specific project requirements.
Don't write what can be more easily drawn and vice versa.
Avoid prescribing working methods and order of work, unless there are
specific requirements in this regard.
Use existing standards and codes.
Standardise as far as possible, but remember that different areas have
different climatic conditions, etc., which may require specific or special
treatments.
Words and terms which are often used in specifications, but should be
avoided:
“Best" or "highest quality where this is not required. Materials, etc.,
come in different grades of quality and the appropriate quality should
be specified.
"Proper workmanship". Vague. Rather specify full requirements,
tolerances, etc. May perhaps be used for minor, works.
"or other approved". Introduces uncertainty.
"as specified" is often used without specifying anything anywhere.
Format of specification documents
It is common these days to have a specification in two parts: A standard specification based extensively
on existing standards and
codes of practice (such as the “Model Preambles" published by the
Association of South African Quantity Surveyors) which is bound in a
separate document and is included in the contract by reference only.
A particular or "works" specification which contains the specific description
and requirements of a particular project, including any deviations from,
or supplements to the standard specification. This part usually also
contains the schedules of finishes, fittings, etc.
Sources of information for specification
Projects completed or underway for same client
This may seem so obvious as not to warrant mentioning. In practice,
however, specifiers often base their choices only on a verbal or written
brief from the client whereas it may have been useful also to visit the
client's and/or similar types of operations, speak to managers and
operatives who use the facilities and observe for oneself the performance
of various materials and components in use over time. This also brings
us to the concept of performance rather than prescriptive specification
where the former may often be the more appropriate format since it
allows for greater competitiveness and innovation among tenderers. It
goes without saying though, that the different proposals offered on this
basis, will require great care, true understanding of the functional or
performance requirements, and knowledge of the alternatives in the
evaluation process.
Books, journals and manuals on construction science and practics
These are excellent and comprehensive sources of information, but
remember that they are often written for use in other countries where
different standards, practices and climatic conditions may apply.
Therefore, always test the applicability of such information to local
conditions, and amend where necessary.
The Government, or State Library in Pretoria keeps a copy of every
formal publication brought out in South Africa.
Many libraries, especially these at universities and research bodies
such as the CSIR, have electronic access to international data bases
which provide access to information.
Trade journals often have a section devoted to product news.
Some useful locally produced publications are: Model Building Specifications Standards Guide for
Architects,
compiled by HW Wegelin and available from most bookstores, or
from the practice KWP Architects in Pretoria.
A iechnical guide to good house construction, prepared by the then
National Building Research Institute of the CSIR in collaboration
with the ther. Association of Building Societies of South Africa,
available from the CSIR.
The National Home Builders Registration Council's Standards and
Guidelines available from the NHBRC in Randburg.
INB)
Specifiers' own knowledge and experience and that of their
colleagues
This is a useful, but often underrated and ignored source of information.
Practitioners should develop the habit of making specific and detailed
notes of building failures (and successes) encountered in the course of
their daily work. These notes can be filed under appropriate headings
or subjects, and used as a data file for future specification writing.
Manufacturers' brochures, catalogues, installation manuals, etc.
These can be obtained from manufacturers directly, for instance by
calling out sales and/or technical representatives for a visit, from larger
building materials supplier outlets, at periodic fairs and exhibits such as
the annual Interbuild Africa event, at permanent exhibits/building
information centres such as are found in most of the major centres, or
in maintained data filing systems such as Specifile, Klassidex, etc.
The CSIR also sells an electronic data system known as Quantarc to
which one could subscribe.
A note of caution: manufacturers' handouts are often sales orientated
and omit to mention limitations on the use of their products. Interviews
with technical/sales representatives should take this into consideration,
and should wherever possible be followed up with calls and/or visits to
references where the product is already in use.
Specifying by trade name only also carries potential risk for the specifier
since the contractor is not usually responsible for latent defects in
materials and goods specified by trade name (e. g. clause 8.3.10 of
JBCC contract).
For comparison and evaluation purposes, product information should
be arranged under at least the following headings:
Product name, manufacturer and description
Technical data
Installation guidelines
Availability and costs
Guarantees
Maintenance requirements/procedures
Technical services available from manufacturer and/or its agents
Test reports, evaluations, etc.
References
Legislation and regulations
Specifiers often unthinkingly refer to the National Building Regulations
(NBR) without taking cognisance of the fact that the NBR are not
necessarily a handbook for good building practice, but rather a set of
guidelines orientated towards defining:
(a) design parameters, and
(b) the relationship between building owners and public (mostly local)authorities,
primarily with a view to requirements for the health and safety of building
occupants and the public using such buildings (Refer to section 11.8.1
for more detailed information on the NBR).
Other pertinent legislation of which specifiers should have a basic working
knowledge is the Occupational Health and Safety Act 85 of 1993 and
Regulations (OHS Act).
Souti. Africari Bureau of Standards (SABS) codes and standards
(Refer ic section 11.7.1 for more detailed information on the SABS)
The SABS annually publishes a catalogue of South African standards
and related publications which is obtainable from the SABS, Private
Bag X191, Pretoria, 0001 (1997 price: R60,00 plus VAT and postage).
The catalogue contains a short description of each SABS standard and
code of practice, as well as number and subject indexes of the standards
and codes. The actual standards and codes are also obtainable from
the same address and are arranged in groups ranging in price from R8,50
to R270,00 for the group, plus VAT, a 7% handling charge and postage.
Whereas SABS standards for building materials can usually be referred
to without further concern, codes of practice to ensure proper standards
of workmanship need to be studied and interpreted before inclusion (in
whole or in part) in tender documents. It is also important to know that
SABS standards are often minimum standards and may in fact not be
adequate in cases where a higher standard is required. On the other
hand there may be cases where the SABS standard is in fact not required
and insisting on it in the specification may serve only to chase up costs
unnecessarily.
The catalogue is updated monthly in a supplement to the SABS Bulletin
which may be obtained from the Corporate Communication Division of
the SABS free of charge.
One SABS document which may be of specific interest to specifiers is:
SABS 0400 (1990): South African Standard Code of Practice forthe application of the National Building
Regulations.
Specifiers should also be aware of the so-called Compulsory
Specifications which were declared such by the Minister of Trade and
Industry in terms of section 22(1)(a)(i) of the Standards Act 29 of 1993.
Some of these which may apply to buildings and building work are:
VC 8008 : Plugs, socket outlets and socket outlet adapters(Schedule no. 6)
VC 8035 : Earth leakage protection units
VC 8036 : Moulded-case circuit-breakers
VC 8039 : The safety of starters for tubular fluorescent lamps
(The VC numbers refer to SABS internal numbers for administrative
purposes.)
Council for Scientific and Industrial Research (CSIR), Division of
Building Teciinology (Boutek) reports and publications (Refer to
section 11.7.2 for more detailed information on the CSIR)
Agrémeni certificales and NANTAG approvals (Refer to section
11.7.3 for more detailed information on the Agrément System)
Agrément SA is a statutory body which evaluates and approves innovative
building materials and systems. It publishes a monthly Directory of
Certificates and Licence Holders, which is available from Agrément SA,
PO Box 395, Pretoria, 0001 [Tel. (012) 841-3708, Fax (012) 841-2539].
Detailed information about approved materials and systems can be
obtained by purchasing the actual certificates which contains technical
details.
Sundry sources of information
Institutes and Associations such as the Cement and Concrete Institute,
the Clay Brick ivianufacturers' Association, the Concrete Masonry
Association, South African Lumber Millers Association (SALMA), etc.
often publish manuals which provide guidelines for proper practice in
the use of members' products and systems.
Professional membership bodies also produce practice notes and
manuals for use by their members, and professional firms all have
examples of specifications drawn up for previous contracts.
Specification for maintenance work
Whereas specifications for building work normally serve as supplement to
the drawings, and describe a finished product, or end result, specifications
for maintenance work will often not be accompanied by drawings, and will
rather describe periodic or ongoing activities required to keep a building or
building component in good shape, or a service installation in working order.
11.5.2 Nieasurement of building quantities
What is measuremeni of building quantities?
The drawings and specifications for a particular project show the finished
product or completed building. In order to estimate the cost and then price
the work, order the correct amount of materials and allocate resources such
as labour, plant, etc., to the project, the quantities of materials and labour
involved need to be "measured" or "taken off the drawings and set out in
a format which allows the abovementioned processes to take place in a
systematic way, as in the example below:
ELEVATION 1:50
3000
3 280
PLAN 1:50
7
Figure 11.1 Screen wall
220
500
1 870
• SECTION1:50
SCREEN WALL
NGL
Measurement of quantities for this screen wall
(1) Excavate for foundation (surface) trenches – 3,28 m (3 000 mm +140 mm + 140 mm) x 0,50 m x 0,37
m (200 mm + 170 mm) = 0,61 m3
(2) Unreinforced concrete (1:4:5) in wall footings – 3,28 m x 0,50 m x0,20 m = 0,33 m3
(3) One-brick wall laid in stretcher bond in 1:5 cement mortar –3,00 mx 2,04 m (1 870 mm + 170 mm) =
6,12 m2
Summary - measured quantities
(1) Excavate for foundation (surface) trenches:0,61 m3
(2) Unreinforced concrete (1:4:5) in wall footings:0,33 m3
(3) One-brick wall laid in stretcher bond in 1:5 cement mortar: 6,12 m2
From the above quantities for measured items we can now calculate
the component amounts of material and labour required for each item
and use those as a basis for pricing, ordering and resource allocation
for the construction of the wall.
Principles and meinods of measurement
The key to accurate and easy measuring is to have a systematic set of
principles/rules and consistently work to it. Some of these are listed below:
Checking of drawings, etc. Ensure that all drawings as listed on the list of drawings have been
received and are the latest revisions.
Stamp each drawing with the date of receipt and what the purpose
of the drawing is, e. g. "Estimating”, “Bills of Quantities”, etc.
Study the drawings carefully to acquaint yourself thoroughly with
the job.
Check for obvious errors and omissions and check that dimensions
add up. Check for discrepancies between drawings and
specifications. Notify the architect/engineer of errors so that the
drawings can be amended as necessary.
Add up and fill in overall dimensions where it has not been done.
Prepare a query sheet as follows:
Query
1. External face-brick typespecified
2. Size of opening in westwall of kitchen
3. ... etc.
Answer
Rosema Antique Autumn
1 200 mm x 1 500 mm
Supplied by
J Smith
(Architect)
J Smith
(Architect)
Date
16/05/97
21/05/97
Mark up drawings with corrections/answers to queries as supplied
by architect/engineer and after measurement return together with a
copy of the query sheet to the architect/engineer for updating.
Preparation for measurementNumber and provide identification for dimension sheets ("dim"
sheets).
Prepare a cover sheet for the measurements, with all information
pertaining to the job.
Compile a measurement framework, i. e. list the elements to be
measured and allocate responsibility (if more than one person is to
measure on the job).
Example:
(a) Foundations and surface beds
(b) Superstructure (walls, etc.)
(c) RoofsExternal finishes (walls)
(e) Internal finishes (walls)
(f) Floor finishes
(9) Ceilings and finishes
(h) Doors and adjustments
(i) Windows and adjustments
(i) Plumbing and drainage
(k) ... etc.
Mr ABC
Mr DEF
Mr GHI
Mr DEF
Mr DEF
Mr ABC
Mr GHI
Mr JLM
Mr JLM
Mr JLIN
Prepare schedules or tables in which similar work can be grouped
together to avoid duplication of effort.
Do "collects" of dimensions which are common to several items in
order to avoid unnecessarily long calculation or repetition of
calculations.
>>>
Principles of measurement
>>>
Use headings and sub-headings to provide a clear picture of the
measurements. Measure in a logical sequence of items related to
for instance the order of elements.
Measure gross at first and deduct later for openings, etc.
Use preambles to avoid repetition of long descriptions.
Write notes to:
explain the measurements.
assist anyone who has to work with the dimensions at a later
stage, e. g. Final Account stage.
ensure that items which cannot be measured at time of
measuring due to lack of information are not left out at the end
(“To take" notes).
Make sure all dimensions are properly referenced in relation to
location of items on the drawings.
Use abbreviations such as “e. o. o. b." ("extra over ordinary brickwork").
Use "a. b." ("as before") where items are repeated later, and "ditto"
where similar items follow each other, but beware the incorrect use
of these terms.
Where the same dimensions are applicable to a group of items,
write the dims only once and separate the items with "&" ("and").
Where dims have to be calculated, show calculations in the
margins.
Where quantities cannot be determined accurately at measuring
stage, mark them "PROVISIONAL" for accurate remeasurement
later (e. g. foundations where the final depth can only be determined
on site).
Provide provisional sums or prime-cost items (PC-items) for work
which cannot be measured or has not been specified respectively
at the time of measurement.
Dimensions are always written down in the same order, i. e.:
(a) Horizontal at right angles to the line of sight.
(5) Horizontal parallel to the line of sight.
(c) Vertical.
1 000
2000
2,00 x 1,00 x 0,90
Figure 11.2 Order of writing down dimensions
Note: Using figured dimensions (dimensions written down on thedrawings) is always preferred to scaling
of dimensions with a
scale rule.
INB
Further processing of measuremenis
if measurements are to form part of bills of quantities, in order to be really
useful, the raw measurements as taken off the drawings need to be further
processed. This usually includes the following processes:"Squaring” of dims (working up of calculations).
“Abstracting" of dims (adding together in one item of each kind the dims
from all identical items dispersed through the measurements, and
arranging the items into the final correct sequence or order).
"Billing” of items (final editing and writing up of full descriptions in formalform for typing of bills of
quantities.
Note: Quantities are given in the unit of measurement (m3, m2, m, no., t, etc.)which best fits the nature
of the item and allows material and labour (NB
components to be calculated from it with ease and accuracy.
(All processes are checked and corrected and never Isy the same person
wilo carried out the process.)
Corrections are done by deleting original dims in a way which still leaves
them legible and writing the new dims above or next to them.
Different methods for measuring building work used in South AfricaAccurate and detailed quantities
measured for inclusion in bills of
quantities, in accordance with the Standard System of Measuring Building
Work, sixth edition (1991) issued by the Association of South African
Quantity Surveyors in consultation with the Building Industries Federation
South Africa (BIFSA).
BUILDING PRACTICE
VOLUME 2
This method is used to provide a fair and common basis for obtaining
competitive tenders from contractors when a building project is intended.
Accurate, but less detailed and more inclusive quantities measured for
inclusion in bills of quantities in accordance with the Standard System
of Measuring Building Work for Small or Simple Buildings, first edition
(1991) issued by the Association of South African Quantity Surveyors in
consultation with the National Association of Home Builders (NAHB)
and the Building Industries Federation South Africa (BIFSA).
This method is used as above, but for small or simple buildings such as
low-cost housing, etc.
Accurate and detailed quantities measured for inclusion in schedules of
quantities in accordance with Civil Engineering Quantities (1990), issued
by the South African Institution of Civil Engineers.
This method is used as above, but for civil engineering contracts.
Inclusive quantities as measured off sketch plans or final drawings, for
purposes of:
estimating (client or QS)
cost planning and budgeting (client or QS)
tendering (contractors) where no bills of quantities are available
such as on Lump sum Contracts.
Inclusive quantities can take the form of: so-called "builder's quantities” or “rough quantities”
(measured as for
bills of quantities but with more inclusive, built-up items and less
detail).
elemental analysis (one item for each component or element of a
building).
Example:
"Strip foundations for external walls102 m @ R36,30/m
Build up of rate/m:
Excavations: 0,6 x 0,5 @ R25/m3 R 7,50/m
Concrete: 0,6 x 0,2 @ R240/m3 R28,80/mTotal rate R36,30/m
=
R3 702,60"
Lists of labour and materials prepared from anyone of (i) to (iv) above,
or from measurements specifically taken off for the purpose. Labour or
material components are given in the unit, and to the sizes, lengths, etc.
in which they are commonly supplied on the market. Although there is
largely correlation with the way quantities are given in other formats such
as bills of quantities, there are significant differences.
Example:
A Bills of quantities item for timber in trusses (quantity made upas follows: 3,6 m - 2/2,7 m = 9,0 m):
“A1 38 x 114 mm Sawn South Africanpine grade V4 timber in trusses in
lengths exceeding 2,4 m and not
exceeding 3,9 m
List of materials jiems for the same:
"B1 38 x 114 mm Sawn South African pinegrade V4, 2,7 m long
"B2 Ditto, 3,6 m long
Lists of materials are compiled for:
estimating (pricing) purposes
ordering purposes
m
9"
no. 2"
no. 1”
Provisions must always be made for breakage and waste, as well as
lapping as specified.
Wisasuring for maintenance work, repairs, refurbishmeni, alierationis
and additions
Anyone of the above methods can be used, depending on the information
available and degree of accuracy required. It is very important though, to
measure in such a way that the contractor is given discretion to decide for
himself the extent of risk, "overbreak” and waste, etc., in order to price as
competitively as he or she wishes to. This means the more inclusive methods
of measurement are probably better suited to this kind of work.
It stands to reason that a lot of measurement for the above types of work
will be done directly on site, rather than off the drawings.
BUILDING PRACTICE
VOLUME 2
11.5.3 Estimating and pricing by contractors for tenderingpurposes
Brief explanation of basic conceptsDifference between pricing (= estimating) and costing (= recording of
historical fact): Pricing is basis of contract for payments, adjustments
and financial control. Costing is recording actual costs paid and
checking them against the tender "allowables", basis for claims (if any),
financial control, and information for correction of estimating for future
tenders.
Once submitieci, is the tender price fixed for the duration?
Depends on type and conditions of contract, changing circumstances,
contractor's acumen, client/professional team.
Elements of a price:
Direct on-site costs (labour, material, etc.)
Indirect on-site or site overhead costs
(Preliminaries = temporary works and
services, insurances, supervision, certain
plant, etc.)
ESTIMATED COST
General ("head-office") overheads
(rent, salaries, water and lights, financecharges)
+ Profit = Selling price (tender)
(Optional: intangibles, e. g. risk of waste, loss, damage, etc. – manage/
price/insure?)
Some aspects of the process
Quantify the work for pricing: Familiarise yourself with documents, site, general environment.
Decide on appropriate method for quantifying/measuring (accurate
or inclusive quantities).
Prepare for measuring.
Develop and practise systematic routines to ensure speed, accuracy,
consistency and legibility. (Remember measuring is the one part
of the process that doesn't usually get checked.)
Steps in processing quantities:
Write down dimensions in easy format.
Arithmetic: multiply and add up ("squaring and checking).
Abstracting (sorting of items and collation of quantities).
Billing (writing up in final form).
Breakdown each item of work into its constituent elements and build up
rates/prices:
labour
materials
plant
1
Evaluate and decide:
Use labour constants, mix tables, wage
tables individual resource rates, clusters,
programming and resource-allocation.
plant : hire or buy
labour : own labour, subcontractors, labour-intensive or plantintensive approach
materials: bulk or convenience buying, central yard or direct delivery.
Waste factors:
breakage in transit and short delivery
on-site waste:
breakage and loss during movement, mixing and installation
loss through theft and pilfering (part of risk managementcannot really price in typical competitive
environment - manage/
insure)
overlapping (side and end-lapping).
Other risks/intangibles:
Inflation/escalation
"Cash-flow" type costs/discounts (interest, trade, cash and
settlement discounts)
Negotiables
Some examples of detailed cost estimating for tendering purposes are given on
the following pages:
EXAMPLES OF DETAILED ESTIMATING OF COSTS FOR
TENDERING PURPOSES
ESTIMATING COST OF LABOUR
1. General worker (wage band R6,00 +)
Basic wage
Contributions by employer (bonus, holiday fund,
medical, etc.)
Other contributions by employer:
1. BITS (Building Industry TrainingScheme)
2. Accident insurance
3. Unemployment insurance (UIF)
TOTAL CCST TO EMPLOYER
2. Tradesman (wage band R15,00 +)
Basic wage
Contributions by employer
Other contributions by employer:
1. BITS (Building Industry TrainingScheme)
2. Accident insurance
3. Unemployment insurance
TOTAL COST TO EMPLOYER
1,50% = R0,11
2,75% R0,21
1,00% R0.07
1,50% =
2,75%
1,00%
=
R0,28
R0,51
R0,19
R 6,00/hour
R 1.47/hour
R 7,47/hour
R 0.39/hour
R 7,86/hour
R15,00/hour
R 3,58/hour
R18,58/hour
R 0.98/hour
R19,56/hour
Multiplying the above rates by labour constants (the average time it takes a worker
to carry out a certain task) gives the estimated labour cost for a given activity.
Labour constants are obtained through a process called work study (observation
and recording of rates of output over a period of time and under varying
conditions).
Example:
It takes one labourer 1,31 hours to excavate 1 m3 of soil. Using the rate of
R7,86/hour in the calculation above, the estimated labour cost of this item
amounts to R10,30/m3 (1,31 hours @ R7,86/hour).
ESTIMATING COST OF PLANT
1. 250 litre petrol-driven concrete mixer (hire rate = + R85,00/day):
1.1 Information:
1.1.1
1.1.2
1.1.3
1.1.4
1.1.5
1.1.6
1.1.7
1.1.8
1.1.9
Purchase price
Scrap value
Interest rate for financing
Anticipated working life
Operating factor
Production weeks
Depreciation method
Fuel consumption
Lubricating oils, etc.
1.1.10 Repair & maintenance
1.1.11
Insurance
R10 000,00
R2 000,00
20% p. a.
11 520 hours
6 hours/day
48 x 5 days/yearstraight-line
2.5 litre/hour
20% of fuel cost
10% of purchase price p. a. RO, 10/R10,00 p. a.
1.1.12 Life in years:
(11 520 - 6= 1 920 days : 5 = 384 weeks - 48 = 8 years)8 years
1.1.13 Yield and work rate250 litre: 12 x per hour
1.2 Annual cost:
1.2.1
1.2.2
1.2.3
1.2.4
1.2.5
Depreciation: R10 000 - R2 000 = 8
Interest: 20% x R10 000 x 0,5
Repair and maintenance: 10% x R10 000
Insurance: R0,10 x R10 000 = R10 x 0,5
Licence fees
per hour = (11 520 + 8) ==1 440 hours
1,3 Hourly cost:
1.3.1
1.3.2
1.3.3
Fuel: 2,5 litre @ R2,20
Lubricants: 20%
Operator: 8+6 X R7,86
PER T:3: = 3! ncur (12 x 250 litre)
R 5,50
R 1,10
R10,48
R1 000,00
R1 000,00
R1 000,00
50,00
R 50,00
R3 100,00
R2,15/hour
R17,08/hour
R19,23/hour
= 16,41/m3
ESTIMATING COST OF BILL ITEMS
1.
1.1
1.2
1.3
1.4
2.
2.:
1 m3 trench excavation (by hand):
Trenches to 2 m: Excavate and throw out (sand)
Cart 50 m with wheelbarrow: 40% x 1,37 hours
Fill trenches: 60% X 1,31 hours
Spread and compact: 60% x 0,65 hours
Worker: @ R5,02/nour (R4,00 - R4,99 wage band)
1 m3 4:4:5 concrete in footings (mixed with mixer):
Material:
2.1.1 River sand: 4/10 * 1,5 = 0,6 m3 @ R65,00/m3 R 39,00
2.1.2 19 mm Stone: 5/10 * 1,5 = 0,75 m3 @ R85,00/m3 R 63,75
2.1.3 Cement: 1/10* 1,5 - 0,033 = 4,54 sk @ R18,00 R 81.82
2.2
Mixer:
2.2.1 Per m3 (see calculation elsewhere)
2.3
Labour:
2.3.1 Carting on materials:4 workers @ R5,02/hour - 3 m3/hour
2.3.2 Carting away concrete:4 workers @ R5,02/hour - 3 m3/hour
2.3.3 Placing, levelling and tamping:3 workers @ R7,86/hour - 3 m3/hour
+ 5% WASTE
TOTAL
3. Cne-brick wall in 1:6 cemeni mortar (i m2):
33 viaterial:
3.1.1 Stock bricks: 110/4000 @ R360/1 000
3.1.2 Mortar: x 0,062 = 0,062 m3
- Building sand: 6/7 * 0,062 x 1,5= 0,08 m3 @ R45,00/m3
Cement: 1/7 * 0,062 x 1,5 =0,033= 0,4 sk @ R18,00
=
=
3.2vixer (for mortar):
3.2.1 R6,42/m3 x 0,062
3.3
Labour:
3.3.1 Bricklayer: 110 bricks/hour= 1 m2/hour @ R19,56/hour
3.3.2 Assistant: 1 worker @ R5,02/hour
Plus: 5% WasteTOTAL
R
R
R
R
R
R 6,69
R 6,69
R 7.86
39,60
3,59
7.25
19,56
5.02
1,31 hours
0,55 hours
0,79 hours
0.39 hours
3,04 hours
= R15,26/m3
R184,57
R
6,42
R 21.24
R212,23/m3
R 10,61
R222,84/m3
per m2
R 0.44
R
0,40
R 24,58
R 75,42/m2
R.3,77
R 79,19/m2
Example of tender finalisation summary used by contractors
Contract:
Client:
Architect:
Type of contract:
Bill of quantities or measured:
Insurance:
Retention:
Quantity Surveyor:
(a) ALL RISK
(6) PUBLIC LIABILITY:
(C) SPECIAL
Retention fund details:
Guarantees;
Release of guarantees:
Payment for material on site:
Terms of payment:
Penalties:
Escalation:
Closing date of tender:
Tender validity:
Time for completion:
Builder's work
Subcontractors
Provisional sums
SUBTOTAL
P&G (.......... %)
Escalation
Financing/Contingencies
NETT TENDER TOTALS
TENDER PREPARED BY:
Wett Price
Financed by:
Financed by:
Financed by:
Maximum retention:
%
TOTAL BUILDING AREA:
Mark-up
PLUS: 14% VAT
TOTAL CARRIED
TO TENDER FORM
Marked-upPrice
TENDER FINALISED BY:
Rate/m2
11.6 CONTRACT ADMINISTRATION
Contract administration involves the whole project team under leadership of
the main agent (architect, engineer or project manager) and usually includes
the following aspects: Site handover and pointing out boundary pegs, datum bench marks,
etc.
Regular site and other project meetings.
Supervision (monitoring quality, time, etc.).
Issuing and updating of drawings, specifications, instructions, etc.
Financial administration (progress payments to contractor(s), pricing of
variations, cost control and cost reporting, cash-flow monitoring,
settling of final accounts).
Final inspections and handover procedures (taking occupation).
Some areas of contract administration which often present problems, or are
not well understood, are:
Delays and extension of time
Retentions/performance guarantees
Breach of contract/non-performance
Insolvency
Payment for materials on and off site
Ownership of materials paid for
Practical completion/beneficial occupation
Patent/latent defects
Contractors' claims
How to deal with provisional sums, prime cost (PC) items, amount for
contingencies, etc.
Practitioners should acquaint themselves well with the legal and technical aspects
of dealing with the above.
11.7 RESEARCH, STANDARDS AND TECHNICALEVALUATION OF BUILDING MATERIALS AND
METHODS (SABS, CSIR, AGRÉMENT, NHBRC)
11.7.1 The South African Bureau of Standardis (SABS)
The SABS is a statutory national standards body set up in 1945 and currently
governed by parliamentary law, namely the Standards Act 29 of 1993. Its primary
responsibility is the development and publication of standards for products and
services.
A simplified definition of a standard, as provided by the SABS itself is “... a
documented agreement containing technical specifications or other criteria to be
used consistently as rules, guidelines or definitions of characteristics to ensure
that materials, products, processes and services are fit for purpose."
The mission of the SABŞ is to contribute, by promoting quality and standardisation,
towards strengthening the economy of South Africa and enhancing the quality of
life of all its people. With regard to building and construction, this includes
ensuring the provision of appropriate quality of materials together with good
workmanship at an affordable price. Specifically it can assist in achieving the
above through: The Code of Practice for the application of the National Building
Regulations: SABS 0400 - 1990
The code assists designers, builders, local authority building control officers,
clerks of works, etc. in the interpretation and practical application of the
National Building Regulations by providing prescriptive provisions to follow
towards satisfaction of the requirements of the regulations.
Building system appraisa!
The SABS assists in the technical evaluation of innovative building systems
and methods carried out by Agrément SA (see section 11.7.3 below).
Building ivaterial Specifications
It is recommended that except in specific instances where requirements
may be specifically for higher (or lower) standards than the relevant SABS
standard, all building materials specified carry the SABS Quality Mark.
Thousands of products already carry this mark under administration of the
SABS.
Building Materials Tesis and Services
If a supplier or manufacturer has not yet obtained a SABS Mark for its
product, the SABS can assist with quality control, training to small and
medium enterprises (SMEs) on interpretation of specifications and on how
to manufacture in accordance with specifications.
Building Quality Monitoring
Quality assurance principles are contained in SABS ISO 9000. The SABS
can also through an appropriate inspection plan, assist any builder, owner
or stakeholder in adhering to these principles.
D
11.7.2 The Council for Scientific and Industrial Research (CSIR) -Building Technology Division (BOUTEK)
The CSIR was created by the government after World War II to provide research
support for South Africa's primary and secondary industries. It was set up as a
statutory body in 1945 in terms of the Scientific Research Council Act. In 1946
the National Building Research Institute (NBRI) came into being as one of the
CSIR's 27 institutes. During its existence (1946-1988) it carried out extensive
research on all aspects of building, published many information sheets and
booklets, organised conferences and assisted both the private and public sectors
in solving building problems and promoting innovation and development in the
industry.
During 1988 the CSIR, in keeping with the changing demands of the times,
restructured extensively. The 27 former institutes were rationalised into 12 new
divisions, one of which replaced the NBRI as the new Division of Building
Technology or BOUTEK.
11.7.3 The Agrément system for technical evaluation of buildingmaterials and methods in South Africa
Agrément is a French word meaning permission or approval.
The population boom and intensive economic reconstruction of Europe after
World War II placed heavy demands for new buildings on the construction industry.
Conventional or traditional building methods, heavily dependent on individual
skilled artisans and manual labour, were unable to cope, and soon all kinds of
innovative (mostly industrialised) building systems started evolving.
The idea of an official and standard procedure for the approval of such innovative
building methods originated in France around 1947, probably in response to the
so-called "Code Napoleon”, laws which placed statutory liability on designers and
builders for the efficient and safe performance of buildings for at least ten years,
and for which insurance cover had to be provided.
Agrément approval as then applied by the French National Building Research
Institute assisted designers, builders, the public regulatory authorities, and the
insurance industry in the evaluation of new methods and insurance risks attached
thereto.
From about 1960, under French initiative, this performance-based approach to
evaluation and specification of new building practice underwent internationalisation.
Today all of the countries in the developed world have similar systems. The
Agrément Board of South Africa was established in 1969 uncier the auspices of
the CSIR.
Agrément approval is meant for new building methods, etc. which are not
adequately covered by existing building regulations and standards. The purpose
is to confer "deemed-to-satisfy' status on such methods in order to assist designers
and specifiers, developers and contractors, local authority building control officers,
finance institutions, government user departments and implementing agencies
such as works departments, etc. in their evaluation and approval thereof.
MANTAG (Minimum Agrément Norms and Technical Advisory Guide) approval
is a second tier certification which grew out of the need for affordable housing
materials and methods, and is meant only for products used in simple singlestorey buildings with or
without waterborne sanitation systems.
11.7.4 The National Home Builders Registration Council (NHBRC)
The NHBRC is a non-government, non-profit section 21 company set up with
government funds, and soon to be governed in terms of the proposed NHBRC Bill.
Its aims are to ensure quality and good building practice, and to protect consumers
and financial institutions providing credit in the home building industry through
compulsory registration of home builders and developers, and the administration
of a national, statutory Defects Warranty Scheme and Fund.
Although the focus of its functions is home building, using contractors registered
with the Council for other work may provide some peace of mind to owners,
clerks of works and professionals. The Council has also published Standards
and Guidelines for housing construction which may be useful for specification
purposes on other types of construction as well.
11.8 BUILDING REGULATIONS
11.8.1 The National Building Regulations
In 1947 the newly established SABS proposed the formulation of uniform building
regulations to replace the various sets of local building regulations and municipal
by-laws applied by towns and cities in South Afric
Between that time and the 1970s two attempts at this, the so-called "Model
Building Regulations” (completed 1964) and the "Standard Building Regulations"
(gazetted in 1970), both of which allowed for voluntary adoption, failed to find
wide acceptance among local authorities and officials.
In 1973 the Bureau (SABS) proposed that a whole new set of National Building
Regulations (NBR) be drawn up which would be less voluminous and prescriptive
than the previous attempts, but still allowing for voluntary adoption.
BUILDING PRACTICE
VOLUME 2
A policy change occurred with the promulgation of the National Building
Regulations and Standards Act 103 of 1977, which made provision for
compulsory introduction of National Building Regulations to override and supersede
all existing municipal building regulations and by-laws. By February 1981 the first
draft of the new National Building Regulations was gazetted for comment, and
after much redrafting and editing finally promulgated in Government Gazette
no. 9613 of 1 March 1985 for enforcement as from 1 September 1985.
This event presented a clear break with past practice in two important areas: It standardised building
regulations across the country, and made its
application compulsory for all local authorities.
It replaced the prescriptive regulations used previously with functional or
performance-based regulations which allow for far greater flexibility,
innovation and competitiveness among designers, contractors, developers
and manufacturers of building materials, components and systems.
11.8.2 Application of the National Building Regulations
The National Building Regulations (NBR) do not set out specific descriptive
prescriptions on how to build. This makes it difficult for users such as designers,
local authority building control officers, clerks of works, etc. to interpret the
regulations correctly, and to know what kind of construction will satisfy the
requirement of the regulations. To assist with this the SABS has prepared a
South African Standard Code of Practice for the application of the National
Building Regulations SABS 0400 - 1990. The code sets out prescriptive provisions
which, when followed by designers, etc. will lead to buildings that will be deemed
to satisfy the regulations.
Each part of the code is divided into 3 clearly identifiable sections, namely:
The regulations
The deemed-to-satisfy rules
Illustrations and commentary for amplification where included.
The difference between prescriptive and functional requirements can be
illustrated by the following examples:
Prescriptive regulation: “Any external wall of a building shall have a minimumthickness of 230 mm and
shall be constructed of
well-burnt clay brick, built in English bond and bedded
in 1:5 cement mortar."
Functional regulation: "Any external wall of a building shall be capable ofsafely sustaining and
transmitting to the foundation all
the loads to which it is likely to be subjected and shall
provide adequate resistance to rain penetration."
It is clear that the latter type allows for far greater freedom in design and
choice of innovative methods. It is also clear though, that a high degree of
technical knowledge, and some time-consuming calculations are necessary
to produce a design that will satisfy the requirement. To make life easier (and
safer) for the user of the regulations, the code offers guidelines such as
minimum thicknesses for walls built from different materials, brick strengths,
maximum lengths and heights of walls in particular applications, empirical
foundation sizes, etc.
It is important to note that the code only addresses the technical intent of
the regulations, and not any legal, aesthetic, economic or other aspects of
building. Local authorities could for instance insist on certain materials for
the exterior of a building on aesthetic, environmental or market grounds,
and refuse to permit another material, even where it is acceptable in terms
of the regulations.
It is also important to note that the regulations and the Act should be read
together.
The Act and the regulations now apply to all areas in the country under Local
Authority jurisdiction. Local authorities and their building control officers are
permitted to allow deviations from the NBR, and where an existing local bylaw is not covered by the
NBR, it will remain in force.
Town-planning requirements are not replaced by the NBR, and where such
a requirement is more restrictive than the NBR, it remains in force.
Title restrictions on older title deeds are not superseded by the NBR, but
appeal can be made to the Minister in terms of the Act to enforce the NBR
where title conditions are based on outdated information.
Innovative building methods not covered by the NBR, will usually be
acceptable to local authorities if based on “Rational design", or accompanied
by an Agrément or MANTAG certificate.
11.9 GENERAL STATUTORY REQUIREMENTS AND THEROLE OF LOCAL AUTHORITIES IN BUILDING AND
DEVELOPMENT PROJECTS
11.9.1 General statutory requirements impacting on landdevelopment and building work
>>
Very broadly speaking, land development and building work are governed
by a planning and regulatory framework which operates at all three levels of
government, namely national, provincial and local government.
>>
On the one hand are the various land, physical planning, development control
and environmental protection acts, regulations and measures - on the other
the National Building Regulations and standards legislation and enforcement
bodies.
On the planning side, control is exerted over: the general spatial structure of development (through, e.
g. physical
planning act, structure plans, town planning schemes, etc.)
land use (through zoning, etc.)
subdivision, consolidation and transfer of land (through acts and land
survey and registration systems)
the type and nature of development (through zoning and development
control measures such as building lines, height and coverage restrictions,
etc.).
On the construction side good practice is enforced through standards, building
regulations, legislation concerning safety, fair employment practices, training
levies, and statutory registration of building professionals, etc. Building
regulations have been promulgated nationally, but are applied locally in each
area.
The steps in the process and the statutory requirements for each step could
be broadly summarised as in table 11.1.
Table 11.1 Steps in the process and general statutoryrequirements of land development and building
work
Step in the process
Acquiring the land.
Obtaining permission to develop on the land.
Planning of development layout, etc. and
servicing the land ready for construction of
top-structures.
Planning and design of the
top-structures (buildings)
Construction phase
Occupation and use
General statutory requirement(s)
* Registration of transfer of title (ownership)at deeds registrar.
* Permission to rezone (change land use) if)applicable.
* Permission to subdivide into smallerparcels of land if applicable.
* Survey and registration of new parcels ofland.
* Approval of layout, design of services, etc.
* Complying with conditions ofestablishment, opening of township
register, etc.
* Rezoning, consent-use approval, etc. incase of existing urban land.
National Building Regulations define
design parameters to ensure publichealth and safety.
* Approval of building plans and permissionto build in terms of town planning
scheme, development control measures
such as building lines, coverage,
height restrictions, etc.
* Statutory registration of buildingprofessionals.
• Compliance with building regulations, approved plans and municipal by-laws.
* Legislation governing safety on site, labour practices, etc.
un Certificate of occupation (completion tolocal authority's satisfaction)
Trading licence where applicable.
* Maintenance of fire equipment, lifts, etc. in terms of NBR and safety
legislation.
Payment for services and of rates
and taxes, etc.
11.9.2 The role of local authorities
A local authority usually consists of two parts, namely: The representative (elected) political side or
"council".
The appointed professional/technical side usually consisting of a number of"departments".
The council is headed by the Mayor, has an executive committee, and their
function is to set policies and approve budgets that will address the development
and other needs of their constituencies.
The service departments have heads of department, headed by a town clerk or
chief executive officer, and constitutes the bureaucracy at local level. Their
functions traditionally included, among others: implementing the policies set by the elected councils;
preparing resolutions, budgets and capital project proposals for approval by
the council;
physical provision and maintenance of services, amenities and facilities such
as electricity, water, sanitation, refuse removal, stormwater disposal, roads
and streets, parks, libraries, clinics, etc.;
emergency services such as traffic policing, ambulances, fire-fighting, etc.;
preparing property valuation rolls and collecting payments for services, rates
and taxes, etc.;
town planning and building control; andtrading licences and compliance with health and safety
requirements, etc.
After decades of a dual system of local government for "White" and "Black"
South Africa respectively, the Local Government Transition Act of 1993 allows for
the transition to democratic, integrated and unified local government in three
phases, viz., Phase 1 (Pre-interim phase) - negotiations to prepare for and leading up to
the installation of transitional local government (completed).
Phase 2 (Interim phase) – following the local government elections of
November 1995 which democratically legitimised the system of transitional
local government, a period of 3-5 years will be allowed for full transition to
political and functional integration.
Phase 3 (Final phase) - consolidation of the new system. The 1998 White
Paper on Local Government defines the more developmental role local
authorities will take on after the elections planned for 1999, and forms the
basis for the Municipal Structures Bill of 1998. The Bill, when it becomes
legislation in 1999, will regulate the structure and functions of local
government at all levels.
The current system of local government is depicted in the diagram below:
TRANSITIONAL LOCAL GOVERNMENT STRUCTURE
Rural areasTransitionalDistrict
Council
(TDC)
Transitional
RepresentativelCouncils
(Trepcs)
TransitionalRural
Councils
(TRCs)
Urban areas
TransitionalLocal
Councils(TLC)
Metropolitan areasTransitional
MetropolitanCouncil
(TMC)
Transitional
Metropolitan
Substructures(TMSS)
Figure 11.3 Transitional local government structure
SECONDARY
STRUCTURES
PRIMARY
STRUCTURES
With regard to land development and building work specifically the role of local
authorities can be summed up as follows: Determining Land Development Objectives (LDOs) through a
process of
consultative Integrated Development Planning (IDP).
Using the LDOs to determine the shape of physical or spatial planning of
their area of jurisdiction in the form of structure plans or similar plans, and
to plan and budget for capital projects. Structure plans are guide plans
which broadly suggest the spatial distribution of land uses, provision of bulk
infrastructure and transportation networks within the area of jurisdiction of a
local authority.
Giving more formal expression to the guidelines in structure plans, by drawing
up and applying town planning schemes which contain development control
measures such as land-use zoning, minimum erf sizes, building densities,
building lines, coverage, bulk and height restrictions, etc.
Enforcing the above through plan approval and inspection, and approval of
applications for rezoning, consent-use, building line relaxations, subdivision
and consolidation of erven, etc.
Ensuring the health and safety of building occupants and the public by
enſorcing the National Building Regulations through the appointment of
building control officers, plan approval, and inspection.
11.10 THE ROLE OF THE CLERK OF WORKS AND THERESIDENT ENGINEER
11.10.1 The cierk of works (COW)
Building contracts usually provide for the right of the employer to appoint a resident
clerk of works at his/her own expense. The clerk of works is a direct assistance
to, and functions with some delegated authority from the architect in terms of: day-to-day management
of the job
setting standards for and monitoring compliance by the contractor with such
standards, and generally monitoring quality of the work
ensuring compliance by the contractor with the drawings, specifications and
instructionsco-ordination of various elements of site supervision.
The COW has no legal responsibility with regard to the contract, but enjoys a
position of considerable trust, and some authority. The COW is not authorised
to issue direct instructions to the contractor. She/he may issue directions, which
become instructions only when confirmed as such by the architect. The role of
the COW should be clearly explained to the contractor at the commencement of
the contract. It is essential that the COW establish a good working relationship
with the contractor's site agent.
"The role of the clerk of works is exclusively that of an inspector who is constantly
on site for that part of the contract period in which his services are considered
necessary and who is therefore in a position to see that the work is properly
executed in accordance with normal construction practices and in accordance
with the specifications. In practice the contractor is advised to take note of the
opinion of the clerk of works regarding defective material and/or workmanship,
either with or without the confirmation of the architect. If the contractor refuses
to rectify the matter he may later have to make reparations at a far greater cost
when the architect becomes aware of the matter.
(NB)
In special cases, for instance if the site is in a remote area, it could be advisable
to give the clerk of works prescribed executive powers. If this is done all parties
must be informed in writing.
Because he is constantly on site he has the opportunity to view all work before it
is covered and can, therefore, keep a record which will be required by the architect,
quantity Surveyor and others. His reports will generally deal with variations,
progress on site, the labourers employed, the weather, material delivered,
information that is needed, in fact anything that may assist the architect in his
administration of the project.
Nevertheless the architect is not exempted from his responsibility by the activities
of the clerk of works, as demonstrated in the old British case of the Leicestershire
Council of Guardians vs. Trollope (1911). As a result of collusion between the
contractor and the clerk of works the ground floor of a building was laid without
damp proofing, which later caused wood rot. The architect was found guilty of
negligence in spite of the unethical conduct of the clerk of works because he (the
architect) had not ensured that this important work was carried out in accordance
with his instructions and that he did not check with the clerk of works or did not
give him specific instructions regarding the importance of the damp proofing”
(Hauptfleisch & Siglé, 1997:47).
The above could be expanded to list some specific duties of the COW as follows:
Seeing to it that correct bench marks and setting out points are used for
setting out, establishing levels, etc.
Checking pavements, neighbouring properties, etc. for signs of damage prior
to contract commencement.
Seeing to it that trees which have to remain are protected, and valuables
found on site handed over.
Checking that safety measures are followed.
Keeping complete site records (site diary).
Reporting to the architect/employer on a regular basis.
Checking and verifying daywork sheets. The COW checks hours worked
and materials used on dayworks. She/he signs daywork sheets "subject to
architect's approval thereof as dayworks”. Most contracts these days will
not allow dayworks or require prior approval for work to be carried out on
daywork anyway.
Keeping as-built records of foundations and services installed and covered.
Checking and recording progress and matters affecting progress.
Keeping a query and answer book on site.
Attending all site meetings.
Checking on proper storage and protection of materials on site.
Explaining/interpreting drawings, specifications, instructions, etc. to the
contractor's staff on site.
Ascertaining the position of existing services and making sure they are not
damaged.
The COW's functions can be briefly summarised as follows: To inspect in detail.
To report concisely.
To interpret clearly.
To record completely.
The COW's weekly report should include at least the following:
Main contractor's daily workforce.
subcontractors' daily workforce.
Materials delivered.
Plant on site and hours used.
Assessment of labour/plant shortages if any.
Causes for delay and assessment on progress.
Daily weather record including time lost due to inclement weather.
Drawings issued to contractor.
Instructions to be confirmed by architect.
Visitors to site.
A good COW:
has a thorough knowledge and understanding of drawings, specifications
and contract conditions,
knows the building regulations, and
develops a sense (early warning) of problems developing on the job, notifies
the architect in good time of his/her concerns, and works with the site agent
to prevent these from becoming serious impediments to progress, quality,
etc.
A COW should not:
give any direction whatever involving financial effect without prior specific
instruction from the architect-in-charge.
make any alteration to any basic detail of the contract particulars without
prior approval of the architect-in-charge.
approve the contractor carrying out any remedial measures that may involve
any workmanship techniques not approved beforehand.
give any directions to the contractor where aesthetic or structural
considerations apply.
sign the contractor's internal vouchers/requisitions, etc. where extra work isinvolved.
It should also be noted that the COW does not normally "pass” foundations. This
remains the responsibility of the architect or engineer. The COW does ensure
after passing of the foundations, and prior to concreting, that the bottoms of
excavations remain clean and dry, sides trimmed, reinforcement not disturbed,
and that mixes, mixing, transport and placing of concrete are all done correctly.
She/he also checks that curing is done, test cubes handled properly, and
formwork/propping left in place for the required times,
11.10.2 The resident engineer
On large, complex projects with high civils or structural content and usually where
the prime agent is a consulting engineer, a resident engineer is often stationed on
site for purposes of contract record-keeping and administration, more continuous
observation of work in progress, and field checks of material and equipment. It
can be said that the resident engineer's duties are similar to that of the clerk of
works on building contracts.
The resident engineer, as part of his duties, may also be sent as observer from
time to time to the plants and workshops where materials and components are
manufactured for use on the contract.
Although the resident engineer's purpose is to reinforce supervision of the work,
this does not relieve the contractor or his suppliers from their first-line
responsibilities with regard to quality control, compliance with drawings and
specifications, etc.
11.11 THE ROLE AND OPERATIONS OF THE BUILDINGCONTRACTOR
11.'11.1 Introduction
Fifty years ago a contractor would undertake an entire project with only his own
team. Today, the main contractor will probably carry out very little construction
work exclusively with his own team. He will normally only carry out the following
tasks in the usual building contract: excavations (except for large-scale
excavations), concrete work (except for reinforced concrete work), brickwork,
carpentry and joinery (except for custom-built cabinet fittings and shop fittings).
It is unlikely that the main contractor will carry out more than 40% of the total
value of the contract, based on ihe aforementioned tasks. Other important
functions that the contractor fulfils are controlling, planning, organising and coordinating the project.
11.11.2 Planning and organisation
Earlier this century the now well-known GANTT chart or bar chart was developed
by Henry L Gantt as an aid to programming construction work. It is simple in
regard to both theory and executability. It consists of a horizontal time and a
vertical activity scale. The estimated duration of the start and completion times
of each activity are drawn up and entered on the chart.
in this way, it is possible to see a series of complicated activities at a glance. See
figure 11.4.
Days
Foundations
Erection of
frame
Cladding
Brickwork
Roof structure
Partitions
Glazing
Roof finish
1 st fit
Plaster work
Exterior painting
Interior finish
Handing over
Figure 11.4 Bar chart
A serious defect in the Gantt chart is that all activities are shown independently,
with the result that if one activity is delayed it is not immediately clear how later
activities will be affected. To overcome this problem, the Critical Path Method
(CPM) or scheduling was developed, which instead of showing activities as bars
against a time scale, depicts them as mutually associated arrows in a network
diagram. See figure 11.5.
33
1,33
Roof finish
(b)
ErectPartiamo
o Foundations 18framework21 Brickwork? tionsIst fit
(18) 18 (3) 21 (2) 32 (1) (2)
0
Roof structure(12)
(2) (14)
Buļppola
33
(8)
Dotted
arrow(0)
Glazing 27.
23.
37 (4) (14) 41
Interior Handling67
41 Plastering 51. finish65. Over
(10)
51 (14) -6567
7.41
Exterior painting!(33)
(2)
Latest event time
Earliest event time
Critical path
Duration of activity (days)
Total period (days)
Figure 11.5 Critical-path network showing the same work asprogrammed in figure 11.4
The duration of each activity is shown (in brackets) underneath the arrow. A
change in an activity is known as an event and there is an event at the start and
finish of each arrow. A dummy activity has no value of its own and merely shows
a connection between two events, i. e. the fact that glazing must be completed
before the plastering, is depicted by a dummy arrow.
The "earliest event time" is calculated by working forward and adding all the
activities together. It is shown above the arrows at each event. If more than one
arrow ends at an event, the highest value is always taken for the sake of clarity.
For example, between partitions and first fit, the earliest event time is 31 days but
the alternative route, via roof structure, takes 33 days and, thus, the earliest event
time is always given as the highest value.
The "latest event time” is found by working backwards and deducting the activity
times from the final value (67), and this is shown under the arrows at each event.
As in the case of the earliest event times, the highest value is always taken for
clarity.
The float is found by deducting the earliest event time from the latest event time
and is given in square brackets under each arrow, e. g. the float in glazing is
41 days less 27 days = 14 days. This float represents the extra time that is
available before an activity must be completed and provides the programmes
with valuable information, as he can now see how much float time he has for
certain activities and can so arrange them that every man has his instructions,
his tools and his materials when he is ready to start a job. The critical path is
the path (paths) of the arrows which connects the event times.
It is thus the path which contains events without any available float. A delay in any
of the activities will have a direct effect on the completion date. The importance
of this to the programmer is self-evident.
PERT (Programme Evaluation and Review Technique) is a more sophisticated
form of CPM (Critical Path Method). For example, where CPM requires one
estimate for each activity duration, PERT requires three time estimates:
pessimistic, most likely and optimistic. In the calculations, the average of the
three estimates is used to establish a duration for each activity.
The PERT network serves all levels of control and can show the interrelationship
between different contractors and their various subcontractors.
11.11.3 Quality control
The contractor is legally responsible for the execution and completion of the work
in accordance with the contract documents, to the reasonable satisfaction of the
architect. Work of this quality will not be achieved without proper organisation by
the contractor. The onus is on the contractor's site manager to ensure that the
standard of the work, including that of subcontractors, whether appointed or not,
meets the contract and reasonably satisfies the architect. The responsibility of the
contractor is in no way reduced by the duty of the architect to carry out periodic
supervision and inspections.
11.11.4 Financial control and cash flow
Financial control is indispensable for good management. During a given period,
e. g. a week or a month, tens or hundreds of tasks can be carried out. Cost
control aims at showing the evaluation or performance against the standard for
all these tasks, as well as its financial effect for the report period plus a total to
date.
11.11.5 Estimation and preparation of tenders
There must be a clear distinction between estimation on the one hand and costing
on the other. An estimate can be described as a pre-assessment of the costs of
a unit in a building, or an entire building, by the summation of the estimated unit
costs. Costing, on the other hand, can be defined as the accumulation of the cost
data during and after the erection of the project or building and its reformulation
in monetary terms to establish whether the project is running at a profit and, if
not, to make changes so that it is profitable. It also assists the estimator with
data for future estimates.
Tender
Preparations
Estimator prepares estimation
Execution phase
Collect information
(Costs)
Feedback of cost information
Contract manager
Foreman
Costing clerk
Figure 11.6 Flow of cost information on a building contract
The final responsibility for the submission of the tender price rests with management.
The price is based on the detailed estimates and calculations prepared by the
estimates division. The tender must be drawn up in a manner that is clear and
consistent, and which takes into account the construction methods and other
circumstances which can have an effect on the execution of the work on the project.
Estimators work closely with construction control and construction personnel and
there is a free interchange of information and knowledge between them.
The systematic contractor should calculate his own quantities when he tenders on
a lump sum basis. Considering that normally he does not have the professional
staff available to compile comprehensive bills of quantities, he usually draws up a
builders' bill of quantity, which is a much more basic and simplified measurement
document in respect of the work to be carried out in accordance with his
interpretation of the drawings and specifications (if any).
Two ways exist in which the contractor can determine his price, viz.:
Net price determinacion
This is a method of estimating whereby the items in a bill of quantities are
priced without the addition of profit and overhead costs. The profit and
overhead costs are added at the end.
The reason for this method is the determination of expected profit.
When a bill of quantities is submitted to a client or the quantity Surveyor
after tender acceptance, all the prices must be converted to gross prices.
Gross price determination
This is a method of estimating where each item in a bill of quantities is
weighted with a percentage for overhead costs and profit.
11.11.6 Contractor's pre-construction activities
After he has signed the contract, or after receipt of an acceptance letter from the
employer, the contractor must:
allocate suitable labour to the contract;
place orders with subcontractors and suppliers that confirm that they can
adhere to the programme, and prepare and sign subcontracts for which
instructions have been received;
arrange the necessary equipment;
arrange for insurance such as required by the contract and obtain confirmation
that subcontractors have made their own arrangements for insurance;
investigate the application of the safety and welfare regulations;
establish the work performance which, subject to approval by the architect,
will be sub-let;
determine and approve the placing of signboards, as well as site huts, storage
areas, etc. Determine service outlets and connections and make a decision
regarding fencing and other security measures that are required;
decide on the samples of materials and sample panels that are required;
approve the dates upon which he must present his requests for payments to
the quantity Surveyor, in relation to the first and following appraisements for
interim payments;
determine the dates upon which the nominated subcontractors will submit
their requests for payments on account, in accordance with the first and
subsequent evaluations for interim payments;
agree with the quantity Surveyor regarding the award of payment of amounts
included in the contract lists with regard to provisional and general items;
establish the procedure for making available the wage and material lists to
the quantity Surveyor for verification, as well as how to handle the fluctuation
clauses, if any;
agree on the procedure by which day work will be authorised, recorded, prices,
as well as signed and included in the valuations for interim payments.
11.11.7 Project site meetings
During the duration of the contract the contractor will be expected to attend
regular progress meetings on site. Separate meetings to handle matters of a
particular technical nature will be called when the contractor considers them
necessary.
Before the date of the meeting the contractor must establish that: the actual progress of the work is
keeping pace with the agreed programmed
progress of the work, as well as what actions are necessary to correct
discrepancies;
a systematic report of the work is kept;
all contractual claims are submitted promptly and are priced according to the
conditions of the contract;
appointed subcontractors are proceeding according to the agreed programme
and that adequate facilities are available to them;
instructions in respect of variations are given or confirmed in writing;
measurements are taken of the work whenever necessary, especially of work
that will be concealed or subsequent work;
day work statements are properly completed and priced before they are
signed by the architect and presented to the quantity Surveyor.
11.11.8 Contractor's own site meetings
The contractor will arrange site meeting which are attended by the subcontractors
and his own personnel to: review the progress and the quality of the work by comparison with the
contract documents, programme, etc., and to initiate investigation into work
which is behind schedule or below standard and decide on remedial steps;
review the programme and, if found necessary after discussions with the
architect, initiate certain revisions with other consultants and subcontractors;
obtain all urgent information that is requested from the architect and
consultants regarding the contractor's and/or subcontractors' work;
initiate an investigation into and consider how to overcome site problems and,
if doubt exists, to refer them to the architect;
consider the labour position, confirm and approve proposed delivery dates
by suppliers and investigate the advance orders;
consider the materials position, confirm and approved proposed delivery dates
by suppliers and investigate the advance orders;
consider the usage of equipment and make arrangements for its availability;
supervise site organisation and site layout and check the working of safety
and welfare regulations;
check the arrangements for the recording and measurement of work in
consultation with the quantity Surveyor;
check if variations are recorded and that day work statements are presented,
priced and confirmed;
check the integration, progress and quality of the work of subcontractors and
specialisi suppliers and to ensure that those who are expected to attend the
next site meeting, or are required to make additional visits to the site, are
advised accordingly;
approve the dates of the next and subsequent site meetings.
11.11.9 Completion
On completion of the contract the following takes place: When the contractor is satisfied that the
building(s) is/are satisfactorily
completed he will, together with the architect, carry out an inspection, during
which a list will be prepared with an explanation of any contract work that has
not been completed, or has been incorrectly executed or is unacceptable, so
that the contractor can take the necessary steps.
The contractor must, as soon as possible after the issue of the certificate of
practical completion, provide the quantity Surveyor with the final particulars
of all variations, remaining day statements and appointed subcontractors' and
suppliers' invoices. This will facilitate the preparation of the final account on
the date stipulated in the contract.
The contractor must arrange to supply the architect with information about
guarantees offered by subcontractors and suppliers regarding their services
and material.
When the quantity Surveyor has prepared the final account and issued his
final statement, the architect must inform the owner of the building of the
amount of the final account.
After all faults have been corrected and the architect is satisfied, he must
certify that these defects have been corrected and, in accordance with the
conditions of the contract, release the balance of the retention money and
issue his final certificate.
11.11.10 On-site process: Some aspects to consider
Building site layout and activity planning
No standard method – each site is different.
Aim is to ensure optimum efficiency, economy and safety by looking at the
implications of tidiness, accessibility and co-ordination.
General guidelines:
Draw up plan or map of site showing access, circulation of people,
materials and machines, position of temporary facilities such as stores,
offices, toilets, sleeping accommodation, etc., as well as the positions
of permanent structures.
Plan where to start with the work and the physical sequence of completion
keeping in mind things such as disturbing occupants of completed phases
and risk of damage to roads, services and buildings or parts of buildings
already completed.
Planning of access (remembering that social housing projects may often take
place on densely built-up inner city areas and involve multi-storey buildings)
should:
ensure ease of delivery of materials and avoid multiple handling.
consider probable size, mass and manoeuvrability of delivery trucks.
ensure that heavy loads are not transported over pipelines, services,
etc.
provide, if possible, two gates in order to ensure one-way flow of traffic
(this does however create a security problem).
if possible make access and circulation routes as permanent and
maintenance-free as possible by proper compaction, grading for drainage
and even hard-surfacing (keep in mind the implications of damage to
permanent roads, etc., by overloading beyond their designed carrying
capacity).
co-ordinate with traffic and other authorities with regard to temporary
closing of streets, pavements, etc. and hoarding for the safety of
passers-by.
ensure that accommodation for staff provide safe and healthy living andworking conditions.
Administrative facilities may include, as required, the following: Offices for supervisors and clerical staff
(store clerks, etc.). Supervisor's
offices should have an optimum balance between best possible views
of the whole site and isolation from dust, noise, interruption, etc.
Communication means: telephone, fax and on large sites maybe eventwo-way radios, etc.
Plant and equipment must be allocated and placed for optimum utility and
minimum wastage. This involves decisions such as central bulk concrete
batching plants against smaller mobile mixers; cranes, hoists or conveyors
for vertical movement of materials, etc.
Temporary services such as water, power, telephones, toilets for staff, etc.
Materials storage and handling:
Multiple handling of materials wastes time and money, increases the risk
of breakage and makes loss control very difficult.
Storage method depends on: Durability of materials (level of protection required against elements).
Protection required against damage, e. g. deformation of windows when
stacked incorrectly.
Protection required against loss and theft.
Remember completed parts of buildings can be used for stores. Keep this
in mind when programming the construction sequence.
Factors to consider when placing stores, etc., and establishing a handling
system: Optimum balance between ease of access for delivery and closeness
to point of use.
Proper control procedures for receipt and issue of materials, tools, etc.
Security
Flow diagram of stock movement to ensure enough materials on site at
all times.
Keep site tidy and remove rubble regularly.
Gravity feeds where possible for bulk aggregates and rubbish removal
chutes.
Organise storage in store so that materials can be easily found and
taken stock of.
Materials and
equipment
delivered to
site
ReceptOffload
of
Site boundary
Store
Handle
Handle
Handle
Combine materials,
e. g. mix concrete
Site pre-assembly
at ground level
Final
location
in structure
Handle
Handle
Figure 11.7 Diagrammatic layout of materials handling on site
Other general factors to consider when planning site layout and activities: Power and lighting for
overtime work on tight programmes.
Confined sites and densely built-up sites: You may have to change the
layout once or more as the site gets covered with buildings. Bear this
in mind in initial layout planning to minimise wastage and remember to
budget for this.
Phased completion and partial (“beneficial”) occupation may necessitate
moving temporary site establishments unnecessarily if not properly planned.
>>>
Statutory prescriptions with regard to health and safety of workers and
passers-by.
Temporary storage and/or removal of excavated material, building rubble, etc.
Space and facilities for on-site manufacturing, e. g. cutting, bending and
assembly of reinforcing steel cages.
Fire precautions (placing of flammable stores).
Especially in the city: potential damage to adjoining properties due to removal
of lateral support in deep excavations and demolitions.
Regulations (local and other authorities) with regard to noise and dust
pollution, demolitions, use of explosives and pneumatic tools, after hours
work, etc.
Accommodation of subcontractors.
Co-ordination of multiple contractors on large sites.
Implications of contracts following on previous contracts (e. g. where
earthworks is done under separate contract before main contractor comes
on site)
QUESTIONS FOR SELF-EVALUATION
1.
Draw up a detailed list of activities and steps involved in the
procurement of a building contract from the stage where the client
has briefed the architect right up to completion ready for occupation.
Show clearly which steps need to be taken by the following parties
respectively:
(a) The employer (client)
(b) The architect
(c) The consulting engineers
(d) The quantity Surveyor
(e) The land surveyor
(0) The local authority - building control section
(g) The contractor
80
REFERENCES
Basson, N. 1996. Passage to Progress: The CSIR's Journey of Change 1945 -1995. Johannesburg: Jonathan
Ball.:
City Council of Pretoria. 1997. Reference Guide for the Owner Builder. Bookletissued by the City Council
of Pretoria and Adcor Marketing.
Cooke, B. 1992. Contract Planning and Contractual Procedures. 3rd edition. Houndmills: MacMillan.
Freeman, C. J. 1985. The National Building Regulations – An ExplanatoryHandbook. Cape Town: Juta.
Greater London Council. 1983. Handbook for Clerks of Works. 3rd edition. London: The Architectural
Press.
Green, R. 1986. The Architect's Guide to running a Job. London: TheArchitectural Press.
Hauptfleisch, A. C & Siglé, H. M. 1997. The Structure of the Building andProperty Industry in South
Africa. University of Pretoria, Pretoria.
Holden, R. (ed.) 1997. The SABS Building Standards for Housing 1997. Johannesburg: Malnor.
Model Preambles Committee. 1995. Model Preambles for Trades. Associationof South African Quantity
Surveyors, Halfway House.
NHBRC. 1995. National Home Builders Registration Council's Standards andGuidelines. Randburg:
NHBRC.
Noy, E. A. 1990. Building Surveys and Reports. Oxford: BSP Professional Books.
Rosenfeld, W. 1985. The Practical Specifier: A Manual of ConstructionDocumentation for Architects.
New York: ivicGraw-Hill.
SABS. 1990. SABS 0400 - 1990. South African Standard Code of Practice forthe Application of the
National Building Regulations. The Council of the South
African Bureau of Standards, Pretoria.
SABS. 1995. The Strategic Importance of the South African Bureau of Standardsin the National Housing
Programme. Pretoria: SABS.
SABS. 1997, South African Standards and related Publications - SABSCatalogue 1997. Pretoria: SABS.
Stanley, C. M. 1982. The Consulting Engineer. 2nd edition. New York: JohnWiley & Sons.
The Aqua Group. 1990. Contract Administration for the Building Team.7th edition. Oxford: BSP
Professional Books.
The Aqua Group. 1990. Tenders and Contracts for Building. 2nd edition. Oxford: BSP Professional Books.
Wegelin, H. W. 1994. Model Building Specification and Standards Guide forArchitects. 3rd edition.
Pretoria: KWP Architects.
NOTES
CONTENTS
LEARNING OBJECTIVES
8.1
8.2
8.3
8.3.1
8.3.2
8.3.3
8.3.4
8.3.5
8.3.6
8.4
8.5
8.6
INTRODUCTION
DEFINING QUALITY
QUALITY MANAGEMENT CONCEPTS
Quality policy
Quality objectives
Quality assurance
Quality control
Quality audit
Quality plan
QUALITY IMPROVEMENT
TOTAL PROJECT QUALITY MANAGEMENT
CONCLUSION
QUESTIONS FOR SELF-EVALUATION
REFERENCES
8
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69
75
76
76
BUILDING PRACTICE - VOLUME 2
LEARNING OBJECTIVES
The objectives of this module are to introduce the student to quality
management and how to apply it in practice to the erection and
maintenance of buildings.
After completion of this module the student should be able to: display a keen awareness of quality
management and the necessity
thereof in building work
apply basic quality management principles during a building process
8.1 INTRODUCTION
Over the last two decades the drive towards quality improvement has been
nothing less than a revolution. The drive being essentially customer driven, who
is demanding according to Kerzner (1995:1039): Higher performance requirements
Faster product development
Higher technology levelsMaterials and processes pushed to the limit
Kerzner (1995:1040) compares the past and present views of quality as per
table 8.1.
Table 8.1 Changing view of quality
Past
Quality is the responsibility of blue-collar
workers and direct labour employees
working on the floor
Quality defects would be hidden from the
customers (and possibly management)
Quality problems lead to blame, faulty
justification, and excuses
Corrections-to-quality problems should be
accomplished with minimum
documentation
Increased quality will increase project
costs
Quality is internally focused
Quality will not occur without close
supervision of people
Quality occurs during project execution
Present
Quality is everyone's responsibility
including white-collar workers, the indirect
labour force, and the overhead staff
Defects should be highlighted and
brought to the surface for corrective
action
Quality problems lead to co-operative
solutions
Documentation is essential for "lessons
learned" so that mistakes are not
repeated
Improved quality saves money and
increases business
Quality is customer focused
People want to produce quality products
Quality occurs at project initiation and
must be planned for within the project
Quality is not to be reduced to a simple concept which relates to the end product
being of a "high" or "low" quality only. Whilst the final evaluation of a product is
obviously the end objective, it is of paramount importance that quality, more
specifically, quality management, is understood as a process. A process with
inputs, converted by management to outputs, the latter in present-day
competitive markets aimed at retaining customers, win back lost customers and
obtaining new ones.
The message from the competitive market environment today is clear: "Do it
right the first time”. This has to be achieved through prevention and process
appraisal, and not by incurring internal failure whilst in production, or external
failure in the hands of the customer.
BUILDING PRACTICE
(D
VOLUME 2
8.2 DEFINING QUALITY
Quality can be defined in many ways. The ISO 9000 definition is possibly the
best description in this instance, the totality of feature and characteristics of a
product or service that bears on its ability to satisfy stated or implied needs.
Quality concepts, according to Kerzner (1995:1042-1043), developed from the
1950-60 period from “sorting of good from bad” to avoidance today, with
underlying principles such as:
The cost of quality
Zero-defect programmes
Reliability engineeringTotal quality control
From the above the present emphasis is clearly on a process of "quality
management” as a "strategic tool", which includes topics such as; quality is: Defined by the customer
Linked with profitability both on the market and cost sides
Has become a competitive weapon
Is an integral part of the strategic planning processRequires an organisation-wide commitment
Bank (1992:15) provides a simplified commercial definition of quality:
Fully satisfying agreed customer requirements at the lowest internal cost.
8.3 QUALITY MANAGEMENT CONCEPTS
Kerzner (1995:1051-1054) states that the following six quality management
concepts should exist in order to ensure that quality management as a “strategic
tool” is established in an enterprise:
8.3.1 Quality policy
The format is a printed statement which states the enterprise's quality principles,
promotes consistence, provides explanation to outsiders regarding quality, offers
guidelines regarding quality and provides for regular updating.
8.3.2 Quality objectives
Quality objectives are a written extension of the quality policy and ensure that
the policy is attainable, it defines specific goals, is understandable and provides
deadlines for achievement.
8.3.3 Quality assurance
A quality assurance system will identify objectives and standards, be multifunctional and prevention
orientated, plan for data collection, plan for maintenance
and improvement of performance, and includes quality audits.
8.3.4 Quality control
Quality control systems select what to control, set standards for decision-making,
establish measurement methods, compare results, prescribe corrective action,
ensure accurate measuring devices and document the quality management
process.
8.3.5 Quality audit
A quality audit ensures that planned quality is met, that products are safe, laws
and regulations met, data is correct, corrective action and improvement are seen
to be done.
8.3.6 Quality plan
A sound quality plan will identify customers and design processes to ensure that
their expectations are met, and that suppliers are included in the process. It is
the embodiment of the quality policy.
The six concepts outlined above should be implemented to ensure that the
enterprise achieves the quality levels that it has set for its products and/or
services.
8.4 QUALITY IMPROVEMENT
From the above it is amply clear that quality improvement is an indispensable
tool in the market place. If ignored, it is only a matter of time before competitors
will take the lead.
Various approaches to quality improvement are sighted by Kerzner (1995:1044)
in table 8.2.
Quality management on site follows the normal management elements approach,
entailing planning, organising, leading and controlling the conversion of inputs to
outputs. Being a process that is managed, there should be well defined evaluation
mechanisms in place as part of controlling outcomes. A typical quality manual
should be devised and regularly updated.
The classic mistake should not be made to regard quality control only as a tool
to ensure “new” products or buildings of a high quality. It is of equal importance
BUILDING PRACTICE
VOLUME 2
to subject refurbishments, alterations, repairs, maintenance and even “re-do"
work to quality management.
Success in any sphere is only achieved if there is commitment, procedures and
people accepting responsibility and accountability.
Table 8.2 Various approaches to quality improvement
LO
Deming's 14 points for management
1. Create constancy of purpose for improvement of product and service.
2. Adopt the new philosophy.
3. Cease dependence on inspection to achieve quality.
4. End the practice of awarding business on the basis of price tag alone. Instead, minimisetotal cost by
working with a single supplier. Improve constantly and forever every process for planning, production,
and service.
6. Institute training on the job.
7. Adopt and institute leadership.
8. Drive out fear.
9. Break down barriers between staff areas.
10. Eliminate slogans, exhortations, and targets for the work force.
11. Eliminate numerical quotas for the work force and numerical goals for management.
12. Remove barriers that rob people of workmanship. Eliminate the annual rating or meritsystem.
13. Institute a vigorous program of education and self-improvement for everyone.
14. Put everybody in the company to work to accomplish the transformation.
Juran's 10 steps to quality improvement
1. Build awareness of the need and opportunity for improvement.
2. Set goals for improvement.
3. Organise to reach the goals (establish a quality council, identify problems, selectprojects, appoint
teams, designate facilitators).
4. Provide training.
5. Carry out projects to solve problems.
6. Report progress.
7. Give recognition.
8. Communicate results.
9. Keep score.
10. Maintain momentum by making annual improvement part of the regular systems andprocesses of
the company.
/continued...
Crosby's 14 steps to quality improvement
1. Make it clear that management is committed to quality.
2. Form quality improvement teams with representatives from each department.
3. Determine where current and potential quality problems lie.
4. Evaluate the cost of quality and explain its use as a management tool.
5. Raise the quality awareness and personal concern of all employees.
6. Take actions to correct problems identified through previous steps.
7. Establish a committee for the zero-defects program.
8. Train supervisors to actively carry out their part of the quality improvement program.
9. Hold a “zero-defects day" to let all employees realise that here has been a change.
10. Encourage individuals to establish improvement goals for themselves and their groups.
11. Encourage employees to communicate to management the obstacles they face inattaining their
improvement goals.
12. Recognise and appreciate those who participate.
13. Establish quality councils to communicate on a regular basis.
14. Do it all over again to emphasise that the quality improvement program never ends.
8.5 TOTAL PROJECT QUALITY MANAGEMENT
The Project Management Institute (United States of America) provides in their
classic book, A guide to the project management body of knowledge (PMBOK)
(1996:84), an overview of project quality management. Figure 8.1 provides the
PMBOK overview of the project quality management processes.
BUILDING PRACTICE - VOLUME 2
Quality planning
1. InputsScope statement
- Product descriptionStandards and regulations
- Other process outputs
2. Tools and techniquesBenefit/cost analysis
- Benchmarking
- Flowcharting
- Design of experiments
3. OutputsQuality management plan
- Operational definitionsChecklists
- Inputs to other processes
Project Quality
Management
Quality assurance
1. InputsQuality management plan
- Results of quality control
measurements
Operational definitions
2. Tools and techniquesQuality planning tools andtechniques
- Quality audits
3. OutputsQuality improvement
Quality control
1. InputsWork results
- Quality management plan
- Operational definitions
- Checklists
2. Tools and techniquesInspection
- Control charts
- Pareto diagrams
- Statistical sampling
- FlowchartingTrend analysis
3. OutputsQuality improvement
- Acceptance decisions
- Rework
- Completed checklistsProcess adjustments
Figure 8.1 Project quality management overview
The need for quality management is primarily aimed at satisfying the needs of
the customer. Slogans such as those of British Airways, “We fly to serve", and
Xerox, “Leadership through quality", are indicative of the quality image which
businesses wish to portray.
Bank (1992:2) underlines in table 8.3 the importance of customer care, without
which the customer simply takes his business elsewhere.
Table 8.3 Display poster for shops, offices, factories and buildingsites
Customers are:
the most important people in any business.
not dependent on us. We are dependent on them.
not an interruption of our work. They are the purpose of it.
doing us a favour when they come in. We're not doing them a favour by
serving them.
a part of our business, not outsiders.
not just a statistic. They are flesh and blood human beings with feelings
and emotions, like ourselves.
people come to us with their needs and wants. It's our job to fill them.
deserving of the most courteous and attentive treatment we can give
them.
the lifeblood of this and every other business. Without them we would
have to close our doors.
(Don't ever forget it!)
The customer is entitled to expect that products and projects should: have a performance specification
that will make it suitable for the intended
purpose
conform to the specification
be reliable and durable for the intended use
offer value for money
be delivered on time
There is general consensus that the quality of products and customer care are
possibly the most important single factors that determine market success. The
cost of quality is often regarded as unaffordable. The fact of the matter is that it
is unaffordable not to have it. Figure 8.2 depicts the cost of quality. The sum of
the cost of failure, cost of tests and cost of prevention (added together being the
total cost) measured against the degree of compliance establishes the lowest
total cost. As total quality management progresses, the degree of compliance
increases, leading to a lower cost of quality.
BUILDING PRACTICE - VOLUME 2
Cost
Minimum
cost
Low
Optimum
Degree of compliance
Figure 8.2 Cost of quality
-Total
cost
Cost of prevention
Cost of tests
Cost of failure
High
Bank (1992:24-54) portrays core concepts of quality management in figures 8.3
to 8.7.
a-O+
M
B
Quality
improvement
A
Sales
Operating
costs
To gain an increase in profit P through increased sales would require a significant
increase A in operating costs (sales personnel, promotion/advertising, inventories,
etc.).
To make the same increase in profit P through quality improvement would requiredonly a fraction of
those operating costs B, which in any case diminish through time.
Figure 8.3 Quality pays for itself in cost reduction
Sales
М.
Customer
satisfaction i
Quality improvement
The more quality improves, the faster sales will increase because customer
satisfaction carries its own acceleration.
As a "quality reputation" grows, marketing can emphasise increasing customer
satisfaction as a major element in advertising and other promotions.
The longer term effect will be to reduce the spending required on advertising tomaintain a competitive
lead.
Figure 8.4 Quality pays for itself in sales growth
Defects/cost
Cost
Defects
Acceptable quality levels are no longer good enough - they imply that a level of
failure is acceptable.
React culture is the norm
(“putting out the fires").
most effort is concentrated on correcting failure
Achieving quality is expensive - defects are reduced over time only by increasingcost through extensive
inspection, checking and progress chasing.
Figure 8.5 "Traditional" quality
BUILDING PRACTICE - VOLUME 2
Defects/cost
Figure 8.6 “Total” quality
Monitor
performing
Cost
Defects
Time
Establish critical
success factors
Determine
best-in-class
performing
Create programmes to
achieve best-in-class targets
Figure 8.7 The benchmarking cycle
Japanese businesses are notorious for their success. Customers around the
world have now reached the stage where they automatically accept that Japanese
products are good. IBM once specified to a Japanese company an acceptable
quality level for components to be manufactured, being 3 defective components
per 10 000 delivered. Their response in writing, as reported in the Toronto Sun:
"We Japanese have hard time understanding North American business practices.
But the 3 defective parts per 10 000 have been included and are wrapped
separately. Hope this pleases.”
In 1979 a Japanese businessman, Konosuke Matsushito (Bank, 1992:36) made
the following statement (which became a fulfilled prophecy):
"We are going to win and the industrial West is going to lose out - there is
nothing much you can do about it, because the reasons for your failure are
within yourselves.
For you, the essence of management is getting the ideas out of the heads of
bosses into the hands of labour. For us, the core of management is precisely the
art of mobilising and pulling together the intellectual resources of all employees
in the service of the firm. Only by drawing on the combined brainpower of all its
employees can a firm face up to the turbulence and constraints of today's
environment.
That is why our large companies give their employees three to four times more
training than yours. This is why they foster within the firm such intensive
exchange and communication. This is why they seek constantly everybody's
suggestions and why they demand from the educational system increasing
numbers of graduates as well as bright and well-educated generalists, because
their people are the lifeblood of industry.
Your socially-minded bosses, often full of good intentions, believe their duty is to
protect the people in their firms. We, on the other hand, are realists and consider
it our duty to get our people to defend their firms which will pay them back a
hundred-fold for their dedication. By doing this we end up being more social
than you”.
The facts about Japan are well known. Quality products from Japan were not
historically the norm. During the period lasting up to about one decade after the
second world war, Japanese products were generally not of a high quality and
regarded as inferior by the western world. The dynamic post war younger
Japanese generation is what really changed it all. They accepted the challenge,
and they have won. Quality on a value for money basis is now globally true and
it is difficult to find any customers today who believe Japanese products are
poor.
8.6 CONCLUSION
The message is clear. If South Africa wants to develop to a first world wealthy
nation such as Japan, Singapore, USA, Britain, Germany, etc., it will have to come
from within. Besides other obvious prerequisites, total quality management will
have to become second nature to all South Africans.
BUILDING PRACTICE - VOLUME 2
QUESTIONS FOR SELF-EVALUATION
1.
2.
3.
Discuss what is understood under the term "quality management".
Name and discuss the six quality management concepts that
should exist to ensure that the enterprise applies quality
management in practice.
Discuss the "cost of quality” and indicate whether it will add or
reduce overall production cost over the long term.
(15)
(20)
(15)
50
REFERENCES
Ashford, T. L. 1989. The management of quality in construction. London: E &FN Spon.
Bank, J. 1992. The essence of total quality management. London: PrenticeHall.
Kerzner, K. 1995. Project management. New York: Van Nostrand Reinhold.
Project Management Institute. 1996. A guide to the Project Management Bodyof Knowledge. USA.