V8.0
Tr
a
in
in
g
Identifying basic constructions
BR
E
Covered in this section:
§ Traditional construction
§ Non-traditional construction
§ Modern Methods of Construction (MMC)
© Building Research Establishment Ltd 2012
32
V8.0
Traditional construction
The majority of houses/bungalows and many low-rise flats in Britain are of brick or
brick and block wall construction, with pitched/sloping timber roofs.
Cavity walls: 1935 to present.
Tr
a
Solid walls: Pre 1850 to 1950.
in
in
g
Solid wall construction was common from the 1800s to 1950.
Cavity wall construction was introduced as early as 1900 in some areas but
predominates from 1935 to the present day.
BR
E
Be aware of different mixes of header and stretcher bonds that require closer
inspection to determine if a cavity is present and if the cavity has been insulated
retrospectively.
Both the above walls are of cavity construction and both show drill holes where the
cavity has been filled with injected insulation.
RdSAP Convention 3.01
Where a cavity wall has been identified, enter as such irrespective of the width of the
cavity.
Additional information on construction types in the ‘Ageing properties and elements’
and ‘Dwelling details’ sections.
© Building Research Establishment Ltd 2012
33
V8.0
Non-standard construction
Definitions and further sources of information
Included here are all constructions other than solid or cavity brick and/or block wall
construction. Essentially they include:
1. ‘Non-traditional Houses’ – systems built between 1918 - 1980:
• Metal framed
• Pre-cast concrete
• In-situ concrete
• Timber framed
g
Note: Both timber frame and system built are often described as non-traditional
construction but they have different energy performances and are therefore identified
separately in RdSAP.
in
2. Modern Methods of Construction (MMC) – Dwellings constructed from the mid
1990’s, whose structural parts are wholly or in part manufactured off-site or on-site by
contemporary methods. It includes complete housing systems built in factories
through to new, site-based technologies.
BR
E
Tr
a
in
Identifying non-traditional and modern methods of construction
Identifying specific construction types, whether non-traditional or modern methods of
construction, can prove difficult. As such if you encounter a construction type that is
unfamiliar to you then you should seek further advice. BRE have published several
key publications to assist surveyors in identifying construction systems:
• BRE Report 469 Non-traditional houses: identifying non-traditional houses in
the UK 1918-75 (below left).
• BRE Report BR282 Timber frame housing 1920 -1975: Inspection and
Assessment.
• BRE Report BR113 Steel framed and steel clad houses: Inspection and
Assessment.
• BRE CD ROM AP149 Non-traditional housing. A collection of 82 previously
published reports and leaflets on specific types of non-traditional houses.
• BRE Trust FB11 Modern methods of house construction by Keith Ross
(below right).
REMEMBER – know your limitations, if this is not your area of expertise then do not
accept instructions for these types of dwellings without further specialist training.
Refer to the BRE website www.bre.co.uk/training for training courses or contact the
team via email energyassessor@bre.co.uk.
© Building Research Establishment Ltd 2012
34
V8.0
Designated Defective
A number of specific non-traditional dwelling types have been designated defective
under the 1984 Housing Defects legislation (now part XVI of the Housing Act 1985)
these are listed below.
Non-traditional dwellings - Designated Defective List
g
Schindler
Smith
Stent
Stonecrete
Tarran Temporary Bungalow
Tee Beam
Ulster Cottage
Underdown
Unitroy
Unity Type I
Unity Type II
Waller
Wates
Wessex
Whitson-Fairhurst
Winget
Woolaway
in
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
in
Airey
Ayrshire County Council
Blackburn Orlit
Boot Beaucrete
Boot Pier and Panel
Boswell
Cornish Unit Type I
Cornish Unit Type lI
Dorran
Dyke
Gregory
Mac-Girling
Myton
Newland
Orlit Type I
Orlit Type II
Parkinson
Reema Hollow Panel
Tr
a
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
BR
E
Expect these types of dwellings to be over-clad and show other signs of remedial
works.
Cornish Unit Type 2: semi-detached – left half over-clad.
© Building Research Establishment Ltd 2012
35
V8.0
Types of non-traditional construction
Metal framed
Principally these comprise steel framed (or steel and cast iron based) system built
dwellings. About 140,000 such dwellings have at some time or other been authorised
for construction in the UK, and many different kinds of system have been used. In
addition to the steel systems there were a small number of aluminium framed
dwellings constructed. The majority of metal framed dwellings would have been
constructed for local authorities, with many subsequently passing into private hands.
Few records remain with local authorities as to their location however BRE Report
BR113 ‘Steel framed and steel clad houses: Inspection and Assessment’ includes a
useful list of locations.
g
Some dwellings date from the interwar period but the majority date from the post
Second World War period. This reflects the need for rapid re-building after the war
and to a certain extent the availability of materials and manufacturing plant no longer
directed to wartime production.
in
in
A common feature of many systems is that the finished dwelling was made to look as
close as possible to conventionally built dwellings, with the preferred finishes either
brick, imitation brick or render. Some of these disguises are nearly perfect and it
takes more than a superficial examination to discover that some dwellings are indeed
metal framed. On the other hand, some are immediately obvious as being of unconventional design e.g. BISF Houses.
BR
E
Tr
a
If it is not obvious that the house is metal frame then the roof space is often the
easiest place to confirm the construction type. The gable or flank wall normally
comprises unlined sheathed metal framing, with the separating wall of metal stud
framing, lined with plasterboard. It may also be possible to see the top of external
wall panels at the eaves from within the roof – where loft insulation does not preclude
access. Sometimes it is possible to identify construction within service cupboards
where linings have not been installed.
Type 3 first floor BISF
Type 3 first floor Riley
It is important to note that the cavities of metal clad houses should not be filled;
external insulation should be used instead. Where cavities are filled there is an
increased likelihood of corrosion caused by condensation.
© Building Research Establishment Ltd 2012
36
V8.0
Pre-cast concrete
It is reported that around 284,000 dwellings in England have concrete panels as their
predominant wall structure. The earliest being constructed during the 1920s but the
majority being constructed during the 1950s and 1960s
There are essentially two types of pre-cast concrete dwelling system:
• Panel systems
• Pre-cast concrete on concrete framing
in
g
Panel systems – These essentially involve producing flat reinforced concrete panel
units in a factory and transporting them to site for assembly. The structural panels
are then stacked on pre-prepared foundations to typically form room or flat sized
boxes. Panels being supplied for use as walls, intermediate floors and roofs. Panels
used as external walls may have the concrete textured or have an external finish
such as brick, tile, paint or sheet material applied to provide an aesthetic finish.
Widely used in high rise developments they were also used for low rise housing. With
low rise developments it was common to use the concrete panels to create a ‘toast
rack’ of separating walls and to use alternative materials for the external walls to the
front and rear of the property. Internally concrete panels were usually wet plastered
but some will have been dry-lined. Note that there are 23 different large panel
systems used in the UK to construct buildings with 4 or more storeys.
BR
E
Tr
a
in
Pre-cast concrete on concrete framing – In a large number of cases the external
appearance of the dwelling will immediately indicate that it is a pre-cast concrete
system built house as the frame and panels are left exposed. However a small
number of systems were rendered externally during construction. Typically the
systems comprise a concrete frame with storey height infill panels. The infill panels
comprise pre-cast concrete panels which span either vertically or horizontally
between the concrete frame. In most cases the infill panels are slotted so that they
engage with the frame. Most systems were two storey and featured pitched roofs, but
there are some three storey Cornish Unit blocks and most Orlit houses had flat roofs.
Cornish Unit Type 1
Cornish Unit Type 2
Be aware that different types can look
almost identical – note the similarities
between the Cornish Unit Type 1 and
Gregory houses.
Gregory
© Building Research Establishment Ltd 2012
37
V8.0
In-situ concrete
Cast-in-situ concrete was used extensively as an alternative to brickwork during the
inter-war period. A number of different systems of cast-in-situ walling were developed
with the intention of lowering costs by reducing construction time. Subsequent
analysis suggests that they were in fact more expensive to build than using traditional
methods. There are several basic types of cast-in-situ construction:
•
•
•
•
•
Single leaf walls with removable formwork
Single leaf walls with permanent formwork
Cavity walls consisting of precast concrete slabs with cast-in-situ concrete
columns
Cavity walls, consisting of precast concrete slabs with a cast-in-situ concrete
core
Cavity walls with removable formwork
g
The concrete mixes specified included dense and clinker aggregates largely
dependent on local sources.
System type
Tr
a
in
in
The most prolific system was the Wimpey no-fines system of which some 300,000
dwellings were constructed between the 1940s and 1970s. No-fines concrete is a
non-proprietary material used extensively in Britain for the construction of both nonloadbearing and loadbearing walls in dwellings. No-fines concrete contains no sand
fraction, and often has a single size stone as sole aggregate constituent. This
produces a honeycomb structure in concrete which gives it a higher thermal
insulation (lower U value) than that of dense concrete.
Number built
BR
E
Wimpey
SSHA
Unit
Easiform Type I
Corolite
Foamed slag
Lamella
Miller temporary bungalow
Weir
300,000
25,000
4,350
2,100
700
200
183
100
100
Concrete thickness
8", 10" or 12"
8" - 10"
8"
8”
8"
9"
8"
10"
In most cases in-situ concrete house walls were constructed as a single leaf and
internally were wet plaster finished.
Wimpey no-fines
© Building Research Establishment Ltd 2012
38
V8.0
Timber framed
These are dwellings in which the loads from upper floors and roof are carried by and
transmitted to the foundations by a timber frame. The claddings are generally nonload bearing and concentrate on providing weather protection and appearance.
There are essentially four types of timber frame construction:
•
•
•
g
•
Balloon frame – two storey height or eaves-height external wall panels, with
studs continuous from ground floor to roof.
Platform frame – storey-height external wall panels which are erected upon
platforms formed by the ground and upper floor construction.
Post and beam – a structural frame of widely spaced timber posts and
beams. Planked, joisted or panelled floor and roof units span between
beams, and non-load bearing infill panels span between the posts to form
the external wall claddings.
Volumetric box – assembled from three dimensional room-sized or storey–
width prefabricated units (see also modern methods of construction)
in
in
Between 1920 and 1944 about 8,000 timber frame dwellings were built for the UK
public sector with a further 100,000 built between 1944 and 1975. Numbers
increased in the private sector during the1960s and 1970s. However, timber-frame
lost favour in the 1980s to conventional brick and block construction. Since the late
1990s they have made something of a come back.
Tr
a
Systems built prior to the Second World War were mostly timber-clad and are readily
recognisable as being of timber frame construction. By contrast, many post war
systems, particularly those built in the 1960s and 1970s, have brick claddings and
are not easily distinguishable from other types of construction of the period. Even so,
in most cases there are particular features that indicate the existence of timber frame
construction.
BR
E
The claddings used for timber frame dwellings include brickwork, tile hanging
(horizontal or vertical) and rendering. These may be used singly throughout or more
often across a dwelling. With brick cladding the windows tend to be set back in the
reveals, and there may be small gaps or soft packing beneath the window frames,
under the eaves and at the tops of verges in order to accommodate differential
movement between the cladding and framing.
Internally, external walls are dry-lined, usually with plasterboard nailed directly to the
timber framing. However those built immediately post war were often lined internally
with fibreboard, possibly fixed over timber boarding.
Scotwood rendered plywood timber frame
1980s rendered block timber frame
As the Domestic Energy Assessor can only carry out a non-invasive inspection of a
property you are likely to be limited in how to identify a timber-frame dwelling.
© Building Research Establishment Ltd 2012
39
V8.0
The roof space is often the easiest place to confirm the construction type. The gable
or flank wall normally comprises unlined sheathed timber stud framing, and the
separating wall is of timber stud framing, lined with plasterboard. It may also be
possible to see the top of external wall panels at the eaves from within the roof –
where loft insulation does not preclude access.
Sometimes it is possible to identify construction within service cupboards where
linings have not been installed. The lining can sometimes be distinguished from drylining to a masonry wall by tapping the lining just above a window: timber frame walls
usually have timber lintels which sound less ‘hollow’ than other types of lintel.
BR
E
Tr
a
in
in
g
RdSAP Convention 3.02
If there is a system built wall that has evidence of retro cavity fill, record as system
build with internal insulation and include Addendum 1.
© Building Research Establishment Ltd 2012
40
V8.0
Modern Methods of Construction
The term ‘modern methods of construction‘ (MMC) covers a broad range of
construction types ranging from complete housing systems built in factories through
to new, site-based technologies. Older terms such as ‘system building’, ‘off-site
construction’, ‘industrialised construction’ and ‘modular construction’ are still used by
many.
A simple classification of modern methods by built form is:
• Volumetric construction
• Panellised systems
• Hybrid construction
• Sub-assemblies and components
• Site based methods of construction
g
The first four categories are usually manufactured in a factory. The term ‘site based
methods’ covers systems that do not fall neatly into the first four categories.
Tr
a
in
in
Volumetric construction
This involves the production of three-dimensional units in a factory. The units are
transported to site where they are stacked onto prepared foundations to form the
dwellings. A typical house is made from four units, whereas flats are usually formed
using two units or with smaller flats a single unit. All of the necessary internal
finishes, services and, potentially, the furnishings can be installed at the factory, with
the complete entity transported to site and assembled. Some external finishes can be
applied in the factory (for example brick slips), but usually some work is required on
site in order to make good between units. To date most volumetric construction has
been used in the hotel, student and key worker accommodation, healthcare and fast
food sectors, however this method of construction is now being introduced to
housing.
BR
E
Panellised systems
This involves producing flat panel units in a factory and transporting them to site for
assembly. These can be constructed in a variety of materials and constructions
ranging from framed panels in timber or steel, to concrete and composite panels
such as SIPs (structural insulated panels). Panel systems are referred to as ‘open’
or ‘closed’. Open panel systems are framing systems (metal or timber) delivered to
site before insulation, services etc. are fitted. Closed panel systems are more
complex and can have services, windows, doors, internal wall finishes and external
claddings fitted at the factory.
Hybrid construction
This method of construction involves a combination of volumetric and panellised
construction. Typically three dimensional volumetric units are used for the highly
serviced areas such as kitchens and bathrooms with the remainder of the dwelling
constructed with panels. They can include a mix of construction and material types
with steel framed volumetric units and timber-frame panellised elements.
© Building Research Establishment Ltd 2012
41
V8.0
BR
E
Tr
a
in
in
g
Sub-assemblies and components
From the point of view MMC, this applies to innovative constructions for floors and
roofs that use engineered products such as timber I beams or lattice joists, which
might be installed on site as prefabricated cassettes. It does not include factory
produced sub-assemblies and components such as door sets, windows, stair strings
etc. which have been used in factory manufactured or traditionally built dwellings for
some time.
Site based methods of construction
This category relates to site-based assembly methods and the use of traditional
components in an innovative way. This includes Tunnelform (cast-in-situ concrete
using heated steel moulds), aircrete planks and thin joint blockwork. Other
innovations include the use of brick slips, insulating formwork and single leaf
masonry.
© Building Research Establishment Ltd 2012
42
g
V8.0
polystyrene permanent shuttering
BR
E
Tr
a
in
in
in-situ concrete
brick slips
brick slips
© Building Research Establishment Ltd 2012
43