CON106 ASSIGNMENT 2
CHRIS TAIT 5036632
Structures for Residential Construction Projects
PREPARE A BUILDING SITE ANALYSIS AND
STRUCTURE DESCRIPTION
Tasks:

Task 1: Site Overview

Task 2: Detailed Structure

Task 3: Alternative Construction method
5 Dargle Way, Island Bay, Wellington
PART 1- SITE OVERVIEW

Choose a site.
65 Albert Terrace, St Martins, Christchurc.
This plot is located on a dead end terrace in St albans, Christchurch. It has an existing
building on the property.
The site is 601m2, zoned residential suburban Zone and marked as within a zone of
liquefaction risk as per the Christchurch council mapping. The site faces a 9% chance of
minor to moderate damage from liquefaction
As visible from the street view below – the property is on a flat surface.
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
Identify and describe parts of the building code which control the type of
construction that can be built on the chosen site
As a general overview, the NZ Building Code (NZBC) sets out the performance standards for
all buildings in New Zealand. As this will be a new build, all of the required standards must be
met to ensure that it meets the legislation (as opposed to older existing buildings).
Generally, this means that we need to be able to show that we comply with the building code
via the use of Acceptable Solutions, a verification method or an Alternative Solution.
Clause A
To start, through Clause A1 we can ascertain that our building is defined as detached
dwelling housing. This is important as it will continue to define how the building code applies
to our building in later clauses.
We can also see from Clause A3 that our building comes under importance level 2, posing
normal risk to human life or the environment.
Clause B
Clause B covering the stability of the building is a big one for any construction activity. This
clause lays out the acceptable solutions or verification methods for the building to withsand
the loads that will be placed on it throughout its lifecycle.
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Clause B1 sets out the required structural standards that must be met, including how the
building will stand up to live, dead, wind, earthquake and other loads. Importantly, with
liquefaction being a risk at the site we have selected for the building, we will need to take into
account the Acceptable Solutions set out in the revision released in November 2019
(amendment 19). This specifically states that the compliance pathway for foundations set out
in NZS 3604 no longer applies to buildings in areas of liquefaction risk, and MBIE
recommends that designers follow a specific ‘Canterbury Guidance’ based on the
categorization of the liquefaction vulnerability in the specific area (defined as low, medium, or
high). This property is technical category 2 – so stronger foundations are required for this
area.
Clause B2 – this is related to the durability and ensuring the materials and workmanship of
our build will stand up to the minimum required periods of time. This specifically sets out 50
year life of the elements difficult to replace (walls, floors, fixings), 15 years for moderately
difficult to replace (envelope, plumbing) or 5 years easy to replace (Services, linings,
protective coatings).
Clause C
Generally – Clause C sets out the minimum requirements for buildings with regards to Fire
Safety. The main consideration that we can apply specifically from our current building is that
as set out under Clause A, our building is importance level 2. This importance level sets
limits of application to some of the provisions of Clause C, that only apply to importance level
3+. An example of this is that the performance requirements set out through C5.5-C5.8 do
not apply to our current build, this covers fire service vehicle access, access to large firecells
etc.
Overall, we will need to ensure that we meet the minimum provisions for preventing fires
occurring, fire spreading, access and structural stability
Clause D
Section 47A of the building act specifies that housing is not held to the same standards of
access as buildings with Public access – so objective d1.1(c) which specifies access routes
for people with disabilities will not apply. Clause D2 will also have minimal to no relevance as
we would not be having any mechanical access.
Beyond this our house will need the standard requirements of allowing safe access into and
our of the building.
Clause E
Clause E covers moisture control in the building.
E1 – surface water sets a greater standard for housing, stating that surface flooding up to a
2% risk of happening annually must not be able to enter the building. This sets specific
requirement of the drainage and minimum clearance to the top of the slab/foundation of that
specific building.
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Otherwise, it is important that we consider drainage in the planning of our site works and
construction to reduce the risk of surface water accumulating and mainage the outfall so that
it is not becoming a risk to other’s property.
E2 will come down to our building having the required design and workmanship to prevent
the ingress of water through the external envelope, including the roofing, cladding,
underfloor.
E3 Standard requirements for reducing the moinsure in the home thorugh appropriate,
ventilation hydraulic design, fixtures and appliances.
Clause F
This clause manages the hazards from the construction stage and the ongoing safety of the
building.
This will always have relevance for our construction, however as we are building a single
story house, a number of the clauses will have little relevance or limits on application as we
will not be having as much consideration around managing safety from falling for example, or
required to make planes of glass visible with manifestations as we would in a building that
will have public use. Similarly, Clause F6 has a limit of application as normal houses are not
required to have lighted escape routes.

Determine if the new-build design is suitable for the site or if it will require
modification to comply with the relevant legislation.
Some of the key information that would lead us to be able to decide if this building complies
with NZBC has been left off. The assumptions based on the appearance of the design I have
made are that the current design is a traditional slab on ground design. This may present two
issues for the way the legislation governs this area:
1. The liquefaction risk in the area as described by the Canterbury Guidance amendment
means that a traditional slab on ground would not be suitable as this is a technical
category 2 site.
2. The ground clearance that we achieve from the bottom of our cladding would need to
be suitable to the potential flooding in the area.
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PART 2 – DETAILED
STRUCTURE

Identify and describe the structure which can be built in more detail
a. Identify and describe the zone requirements from the district plan
Based on the Christchurch District Plan, we can establish if we meet the below
requirements for a residential unit in the Residential Suburban Zone:
Requirement
14.4.2.1 Minimum site are of 450m2
14.4.2.2 Minor residential units: 5.5m max height and
single storey only
14.4.2.3 Site coverage of max 35%
14.4.2.5 Outdoor living space minimum area of 60m2
and minimum dimension of 6m
14.4.2.6 Daylight recession planes
14.4.2.7 Minimum Set back from internal boundaries
14.4.2.9 Road boundary building setback
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Met?
Yes
No dimensions provided on
drawings but logically Yes
No – our build takes up roughly
37% of the site. It may require
slight downsizing. This could be
achieved reducing the width of the
house from 17,170mm down to
16000. This would line up perfectly
with the 35% coverage maximum.
This could be achieved by
reducing the proportions of the
garage and parts of the bedrooms
and living room.
No. We will need to extend our
outdoor space in both dimensions,
potentially extending it longer in
the direction of the garage,
creating a 6x10m deck to achieve
the required 60m2
Logically if our building does not
exceed 5.5 m and is placed
We will need to ensure that our
building is 1m from each internal
boundary. Based on ArcGIS
measurements my site is 17.5m at
the smallest metric, meaning if our
floor plan is orientated with the
13.2m width on this line, we will
have 2.15m each side to work
with.
We can comfortably set out
building back the required 4.5m,
with our property length being
31.2m allowing 17.1m for the
building we have 14m to work
14.4.2.10 Fences
14.4.2.11 Water supply for fire fighting
with. We do have a garage,
however with the orientation we
are using we would not have this
facing the road so would not be
applicable to the 5.5m
requirement.
Set back 1.8m this is not a
problem
This has been set out as per map
below. There is mains reticulated
water supply to the property
b. Recommend and describe a foundation for the new-build design based on
the chosen site. Justify the suitability of the foundation you chose
TC2 specifies that foundations suitable for this liquefaction risk area would be either:
- standard timber piled foundations for houses with lightweight cladding and roofing and
suspended timber floors
Or
- enhanced concrete foundations.
Referring to building performance website, the technical guidance on the weight of cladding
systems is that lightweight cladding solutions are defined as not exceeding 30kg/m2 or
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roofing not exceeding 20kg/m2. Examples of this type of cladding include Weatherboards
(timber, PVC, aluminium), Profiled metal, Sheet materials or exterior insulation and finishing
system. The design of our build includes a brick veneer system, which would not fall under
the lightweight cladding system that would be required for a timber pile foundation design.
This means that the most suitable foundation for our site would be an enhanced concrete
foundation such as the RibRaft TC2 designed by Firth concrete, which has been specifically
designed for TC2 areas. The solutions still require specific engineering from a CPEng –
combination of the pods and reinforcing allow the slab to withstand the temporary loss of
support and differential settlement. The modular formation of the pods gives the slab some
added give to withstand the potential movement that occurs underneath it, as opposed to the
traditional slab which may crack or become damaged under its own weight and lack of
flexibility.
https://www.firth.co.nz/concrete/foundations/ribraft-tc2/
As this is an alternative solution, so would need to be approved via a building consent to be
able to progress to construction which may lead to added costs and time in the design
phase.
c. Describe the design aspects and construction details of a suspended
particle board timber floor for the new-build design that is suitable for the
liquefaction scenario.
Particle board is the standard recommended flooring board for houses on pile
foundations, except for wet areas such as bathrooms (BRANZ 2021). AS/NZS
1860.1:2017 sets out the required standards of the material, also providing guidance
that the flooring is not suitable in areas of high humidity, such as some parts of
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Australia. This is because they are a cheap option and provide a steady surface for
laying flooring finishes such as carpet, tiles, vinyls, however as a material particle
board has low resilience to exposure to the elements/moisture. The acceptable
solution for the use of fibre board is a clearance of atleast 550mm from the ground, to
provide adequate ventilation and a crawl space.
A pile is set in the ground to set the height of the foundations. Then a bearer runs
across all of the piles to distribute the weight. On top of this sits joists that are spaced
appropriately to take the particle boards,
as well as to weight bear the framing to
the walls/roof.
Minimum permitted sizes of bearers from
the Tables 6.4 and 7.1 of NZS 3604 are
as per the image, meaning the clearance
for our timber piles must be 320mm
minimum to meet the required clearance.
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TASK 3 – ALTERNATIVE
CONSTRUCTION METHOD
a. Identify and describe an alternative construction method you could use on
the chosen site
An alternative Construction method could come from an alternative approach to the cladding,
opting for an alternative material so that the design is considered to have a lightweight
cladding. This would open up further options for the foundations, such as timber piles.
Alternative cladding:
An alternative cladding to replace the brick veneer on external envelope of our build could be
an aluminium cladding system. I have selected the Nuwall vertical over cavity, outlined
below:
This cladding system will stand up to the elements, is BRANZ appraised as per NZBC
Acceptable solution E2/AS1 and will open up a lot more options for our building
methodology.
With the lightweight cladding added to our design, we will be able to look at using pile
foundations for our build. Though this is dependant on full geotechnical reports, we will be
able to work to a timber pile system as per NZS3604 as long as we have good ground to
build on. As referenced above, we would ensure a good clearance above the ground level to
allow plenty of ventilation for the flooring and reduce the risk for the particle board flooring
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b. Explain why your alternative construction method would be suitable for the
site
The alternative construction method would be suitable for the site as we know that timber
piles stand up well to the changes in soil bearing capacity that can occur during liquefaction.
Should liquefaction occur, the pile should be deep enough in the ground and supportive
enough to reduce any risk of sinking or shifting in the soil. This is made possible due to the
switch to a lightweight cladding system, so the actual weight of the building does not
compound any changes in the grounds bearing capacity and damage the floor/wall structure.
The added benefit of a timber pile construction is that it makes remediation a lot easier if any
liquefaction related damage does occur. The access underneath the house and the ability to
remediate and re-pile means that we have more options in the future in a worst-case
scenario. We may not have this luxury if a concrete slab requires a large amount of
remediation.
A third benefit of the timber pile solution is that it also provides more options around the
clearance we have from the ground, if we we had any further concerns around flooding in the
area.
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References
Ribraft x-pod structural designers guide (no date) Firth.co.nz. Available at:
https://www.firth.co.nz/assets/Uploads/TechnicalDocuments/XPOD-Structural-DesignersGuide-03052023..pdf.
NZS: 3604:2011
22/08/2023 https://ccc.govt.nz/consents-and-licences/land-and-zoning/technical-categories-map.
Building code update Consultation document MBIE 2019
Canterbury update technical guidance document; build it right Canterbury
Elkink, (2019) Clearance under Particleboard Floor, BRANZ Build. Available at:
https://www.buildmagazine.org.nz/index.php/articles/show/clearance-under-particleboard-floor
(Accessed: 23 August 2023).
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