Getting to grips with the
Canterbury Residential Guidance
- Welcome to ‘Getting to grips with the Guidance’
- This has been designed to help make using the Guidance a little easier
- It’s an overview – we’ll give you links to the Guidance for important, more detailed, information
- Let’s start with some background about the Guidance…
- And here’s Mike Stannard, Chief Engineer at Ministry of Business, Innovation and Employment, to explain a little more about it…
- On this page you’ll also see a menu that will help you find your way around this resource. You can go to any topic, but we recommend that you progress through the topics in order so you have the right context for each topic.
- Topic 1 will tell you more about the Guidance document in detail
- Topic 2 is about Technical Categories 1, 2 and 3
- Topic 3 is about assessing the damage
- Topic 4 focuses on repairing foundations in Technical Categories 1 and 2
- Topic 5 is about rebuilding foundations in Technical Categories 1 and 2
- Topic 6 deals with TC3 Foundations
- We hope you find this useful… and if you have any feedback about this resource, please email us at buildingtraining@mbie.govt.nz
- The Guidance was developed by the Ministry of Business, Innovation and Employment (or MBIE as we are commonly termed) to support the Canterbury rebuild.
- It aims to make it easier to apply a consistent approach to repairing and rebuilding houses damaged in the earthquakes.
- The Guidance set out to free up scarce engineering resources for where they were most needed, and so we established three Technical Categories of the Green zone to help this happen.
- Because of widespread liquefaction in Canterbury, we needed to better understand the geotechnical conditions and provide new repair and rebuild solutions.
- And that’s why a number of experts began the huge task of developing the Guidance following the Darfield earthquake in September 2010. These experts included structural and geotechnical engineers, researchers, and remediation specialists.
- And as you may know, this has been an evolving task - as new research and developments occur, we continue to provide updates and information.
- So, why are we providing this ‘online’ tool now? Well, there are a lot of new people assisting with the Canterbury rebuild who may not be familiar with the Guidance document, and the ongoing updates. We want to make it easier for people to find the information they need.
- Everyone needs to understand the key principles of the Guidance so that we help ‘build it right’ for Canterbury.
This publication is issued as Guidance under section 175 of the Building Act 2004.
ISBN: 978-0-478-43350-0
1. The Guidance
- Welcome to Topic 1, which is about the Guidance for repairing houses in Canterbury
- This topic gives you an overview of what’s in the Guidance and how to use it
- I asked Dave Brunsdon, Professional Engineer and Advisor to MBIE to tell us a little bit more…
Here’s how to get the best from Topic 1:
- Read the Key Principles
- Click on the diagram to get further information
- And click on the questions (bottom right of this screen) to find out more
…and don’t forget, “Build it right, Canterbury!”
- The residential Guidance has been a key element in keeping the technical community on the same page during the recovery, particularly given the nature and extent of the damage to the land and houses
- The Guidance basically represents a triage approach – focusing scarce engineering capability where it is most needed, for the most complex situations. It provides standard approaches to the less complex and more common cases – reducing the level of engineering input required
- Most importantly, it provides repair and rebuild solutions that Councils can be confident about consenting
- The Guidance is updated as we learn more about Canterbury, but the core principles don’t change. Be sure you’re working with the latest version – the online Guidance will always be current and you can check the website for updates. These are typically via Questions and Answers in response to issues and new developments
- The Guidance is divided into five parts –
- Part A provides Technical Guidance for TC1 and TC2 Areas;
- Part B covers Technical Information generally;
- Part C gives Technical Guidance for TC3;
- Part D outlines Geotechnical Investigation Requirements for Subdivisions; and
- Part E covers the complex area of Multi-unit Residential Buildings
- Many of the terms used in the Guidance are unique to the Canterbury rebuild, and we’ll be highlighting some of these in this Topic
There are four key principles that you need to keep in mind…
- Firstly, the Guidance is primarily about repairing and rebuilding houses, especially foundations
- Secondly, while it isn’t mandatory, it does give designers a way of demonstrating compliance with the NZ Building Code – remember, building consent authorities in Canterbury have agreed that building consents will be granted for designs that follow the Guidance
- Thirdly, while the Guidance provides solutions – specific engineering design may also be used
- And finally, as we’ve learned more about Canterbury, the Guidance has been extended
What are the key principles?
- The Guidance is primarily about repairing and rebuilding houses, especially foundations
- While it isn’t mandatory, it does give designers a way of demonstrating compliance with the NZ Building Code — remember, building consent authorities in Canterbury have agreed that building consents will be granted for designs that follow the Guidance
- While the Guidance provides solutions — specific engineering design may also be used
- As we’ve learned more about Canterbury, the Guidance has been extended
NZ’s Building Controls
Building Act
The pyramid diagram illustrates the hierarchy of the Building Code framework, governed by the Building Act.
The Building Act provides the mandatory framework for the building control system to be followed when undertaking building work in New Zealand.
Building Regulations and Building Code
The Building Code is contained in Schedule 1 of the Building Regulations 1992. The Building Code contains compulsory rules for all new building work.
The Building Code sets out performance criteria that building work must meet. It covers aspects such as structural stability, fire safety, access, moisture control, durability, services and facilities, and energy efficiency. The Building Code does not prescribe how work should be done, but states how completed building work and its parts must perform.
An advantage of a performance-based Building Code is flexibility. It contains no prescriptive requirements stipulating that certain products or designs must be used. This flexibility allows developments and innovation in building design technology and systems.
Other specific design
Alternative solutions
Designs that do not follow an Acceptable Solution or Verification Method, but which still comply with the Building Code, are called Alternative Solutions. Alternative Solutions require the approval of building officials where proposed for individual building consents. Alternative Solutions can follow Standards (not already cited as Acceptable Solutions), industry documents or published Guidance, or can be specifically designed.
While the Guidance Repairing and rebuilding houses affected by the Canterbury earthquakes isn’t mandatory, it does give designers a way of demonstrating compliance with the Building Code. Building consent authorities in Canterbury have agreed that building consents will be granted for designs that follow the Guidance.
Acceptable Solutions and Verification Methods
Acceptable Solutions and Verification Methods are not in themselves compulsory but provide details for construction that, if followed, result in compliance with the Building Code. They are published by the Ministry of Business, Innovation and Employment (MBIE). A design that complies with an Acceptable Solution or Verification Method must be accepted by a building consent authority as complying with the Building Code.
Verification Methods are tests or calculation methods that prescribe one way to comply with the Building Code.
MBIE may cite industry documents, such as NZ Standards or industry codes of practice, as Acceptable Solutions or Verification Methods.
Standards
Cited Standards
Helpful links & info
What’s covered by the Guidance?
- The Guidance is in five parts:
Part A deals with repairs and replacement, especially in TC1 and TC2
Part B offers supporting information around things like insurance, land characteristics and ground behaviour
Part C deals with repairs and replacement of foundations in TC3
Part D covers subdivisions
Part E deals with multi-unit Guidance
- The Guidance (PDF 495KB) does cover what you need to know when repairing houses, however, it doesn’t provide specific contract and construction information, so it needs to be used in conjunction with specific contract documentation
How does the Guidance fit with insurance?
- The Guidance principally provides technical information under the Building Code, however it refers to insurance matters in Part B. This provides general context only. It is not a substitute for the agreement you have with your Insurer.
- See Section 8.1 (PDF 955KB) of the Guidance for more detail.
Where can I get copies of the Guidance?
The Guidance is available online via the building.govt.nz website.
2. The Technical Categories
- Welcome to Topic 2, which is about Technical Land Categories in the Guidance
- In this topic we’ll look at land zoning and the three Technical Categories
- Welcome to Nick Traylen, Professional Geotechnical Engineer and Advisor to MBIE, who will tell us a little bit more…
Here’s how to get the best from Topic 2:
- Read the Key Principles
- Click on the diagram to get further information
- Click on the questions (bottom right of this screen) to find out more
…and don’t forget, “Build it right, Canterbury!”
- Technical Categories have been developed to help us broadly understand ground conditions on the flat following the Canterbury earthquakes
- We know that different land areas of Christchurch will behave differently in an earthquake, so we need to build in ways that are designed for that.
- The residential areas on the flat that can be built on are called the ‘Green Zone’ and are divided into three technical categories.
- In this Topic, we’ll explain more about these technical categories and show you where in the Guidance you can find specific information
There are four key principles that you need to keep in mind…
- The Technical Categories exist as a starting point to define the level of geotechnical input needed for a site – they ONLY apply to the flat land areas of the ‘Canterbury Earthquake Region’
- The Technical Categories were established based primarily on observed land and building damage, and also on what was known at the time about ground conditions
- Because of the uncertainty about future performance of TC3 land, deep geotechnical assessments are required for TC3 rebuilds
- Foundations need to be designed to suit the ground conditions. The Guidance provides foundation options that can be used in each of the Technical Categories (these are covered in Topic 3 – Assessment)
What are the key principles?
- The Technical Categories exist as a starting point to define the level of geotechnical input needed for a site — they ONLY apply to the flat land areas of the ‘Canterbury Earthquake Region’
- The Technical Categories were established based primarily on observed land and building damage, and also on what was known at the time about ground conditions
- Because of the uncertainty about future performance of TC3 land, deep geotechnical assessments are required for TC3 rebuilds
- Foundations need to be designed to suit the ground conditions. The Guidance provides foundation options that can be used in each of the Technical Categories (these are covered in Topic 3 — Assessment)
Map of Christchurch
Red Zone
The Red Zone identifies land that is not considered buildable without significant land repair.
TC1 (Grey)
TC1 (the grey area) is part of the overall Green Zone, which is considered ‘buildable’ land. Damage from liquefaction is unlikely in TC1 land in future large earthquakes. Standard residential foundation assessment and construction is appropriate. See Section 3 (PDF 3.75MB) of the Guidance for more detailed information on the Technical Categories.
For foundation options in TC1 see Section 5 (PDF 3.75MB) p 5.1-5.18 of the Guidance for more detailed information.
TC2 (Yellow)
TC2 (the yellow area) is part of the overall Green Zone, which is considered ‘buildable’ land. Damage from liquefaction is possible in future large earthquakes. Standard enhanced foundation options for new foundations in TC2, are provided for this category — see Section 5 (PDF 3.75MB) p 5.4 of the Guidance for more detailed information.
TC3 (Blue)
TC3 (the blue area) is part of the overall Green Zone, which is considered ‘buildable’ land. Damage from liquefaction is possible in future large earthquakes. Specialised foundation types are provided for TC3 — see Section 15 (PDF 2.61MB) of the Guidance.
Helpful links & info
How do I confirm the TC for a site?
To identify the TC of the site, visit the Canterbury Earthquake Recovery Authority (CERA) website.
Once you have this information, you will need to undertake further investigations — see Sections 3.3 and 3.4 (PDF 3.75MB) of the Guidance.
For further general information on TCs go to Section 3.1 (PDF 3.75MB)
Can the TC of a site be changed?
No, however investigations may indicate that a site may be suitable for a foundation that is indicated for a different TC (e.g. a TC3 property may be suitable for a TC2 type foundation) — see Section 3.1 (PDF 3.75MB) Updates of the Guidance.
What do I do for sites that have not been assigned a TC?
Normal consenting procedures apply for land outside the Red and Green Zones. Section 6 (PDF 3.75MB) provides some guidance for hillside properties. Supplementary Guidance is also available for sites in some parts of the Port Hills Area ‘Build it Right’ Supplementary Guidance November 2013 (PDF 650KB).
Where can I get copies of the Guidance?
The Guidance is available online via the building.govt.nz website.
3. Assessment
- Welcome to Topic 3, which is about Technical Land Categories in the Guidance
- In this topic we’ll look at land zoning and the three Technical Categories
- Welcome to Nick Traylen, Professional Geotechnical Engineer and Advisor to MBIE, who will tell us a little bit more…
Here’s how to get the best from Topic 3:
- Read the Key Principles
- Click on the diagram to get further information
- Click on the questions (bottom right of this screen) to find out more
…and don’t forget, “Build it right, Canterbury!”
- The assessment is about working out what has happened to the house and the land
- …and central to this, is understanding the condition of the foundation
- The assessment of foundations determines whether you do nothing, or you repair, or you replace a foundation
- In this Topic, we’ll introduce a process to guide you through an assessment, with a focus on foundations
There are three key principles that you need to keep in mind about Assessment…
- The Guidance provides a process for assessing damage to decide what action to take
- It’s important to consider the ‘whole picture’ - especially site performance, foundation condition and floor levels
- Assessment decisions will always depend on careful and informed judgement
What are the key principles?
- The Guidance provides a process for assessing damage to decide what action to take
- It’s important to consider the ‘whole picture’ - especially site performance, foundation condition and floor levels
- Assessment decisions will always depend on careful and informed judgement
Assessment Steps
Step 1 — Determine the TC the site is listed in
To confirm the TC of the site, visit the Canterbury Earthquake Recovery Authority (CERA) website and then assess whether this matches any land damage on the site.
See also Topic 2 — Technical Categories (in this resource).
Step 2 — Identify the foundation type
Section 2.1 (PDF 3.75MB) of the Guidance explains this in detail.
Step 3 — Measure the floor damage
- It’s useful to divide the floor into a 2-metre grid pattern any identify any other key measurement points, before starting to take your measurements
- Next, calculate the floor slopes between adjacent grid points, covering the whole floor
- Identify the highest and lowest points on the floor. The difference between these is the overall floor level variation.
- Inspect the perimeter of the foundation - you are looking for new cracks. Add up the widths of all the new cracks – the total is the amount of floor stretch
- If it’s a Type A foundation (that is, a suspended timber floor with no perimeter foundation), a careful inspection of the junctions between floor and walls could be helpful in determining stretch
- Now you are ready to move to Step 4
Step 4 — Consult the Guidance for damage limits
Table 2.2 (PDF 3.75MB) and Table 2.3 (PDF 3.75MB) of the Guidance gives us damage limits that help indicate whether to leave ‘as is’, repair, re-level or replace the damaged foundation.
Step 5 — Decide to repair or replace
- Now that you have determined the Technical Category, foundation type and extent of the damage, you will have the basics to be able to make your decision
- Any insurance cover for the property will influence your decision-making. In some cases, it’s possible that the insurance policy will support a level of repair or rebuild that is beyond the recommendations of the Guidance.
- Remember that the decision to repair or rebuild will depend on other factors as well, such as damage above the floor
- Tables 2.2 and 2.3 in the Guidance provide indicator criteria, signalling recommended actions. The decisions are most difficult where recorded levels or slopes are at the intersections of ‘no action’, ‘re-level’ and ‘rebuild’. Other factors that need to be considered include: the construction materials of the floor surface, the practicality of the repair, and what the space is used for.
Case Study #1 (PDF 103KB) Case Study #2 (PDF 177KB)
Section 2 (PDF 3.75MB) of the Guidance.
Helpful links & info
When do I need engineering advice?
For sites in TC3, engineering input is needed to assess the state of the ground and any foundation repair or replacement.
See figures 14.1 and 14.2 (PDF 2.61MB) of the Guidance for more help. TC1 & TC2 require only shallow ground investigation, with Chartered Professional Engineer sign-off needed in TC2.
What do I need to consider about ‘above floor’ assessment?
When doing an ‘above-floor’ damage assessment, you will need to consider framing, bracing, cladding and lining, and chimneys.
For information on these aspects, go to Section 7 (PDF 3.75MB) of the Guidance and Appendix A3 (PDF 3.75MB) of the Guidance for chimneys.
Where can I get copies of the Guidance?
The Guidance is available online via the building.govt.nz website.
4. Repairing TC1 and TC2 Foundations
- Welcome to Topic 4, which is about repairing TC1 and TC2 foundations
- In this topic we will focus on strategies for repairing and/or re-levelling foundations in TC1 and TC2
- Welcome to Graeme Beattie, Professional Engineer and Advisor to MBIE…
Here’s how to get the best from Topic 4:
- Read the Key Principles
- Click on the diagram to get further information about repairing foundations in TC1 and 2
- Click on the questions (bottom right of this screen) to find out more
…and don’t forget, “Build it right, Canterbury!”
- In TC1 and TC2, the repair strategies can be the same
- What you do will largely depend on the ground-bearing capacity
- Repairing foundations may involve combinations of re-levelling, minor repairs, or even replacing part of the existing foundations
- In this Topic, we’ll cover strategies for repairing and/or re-levelling foundations in TC1 & TC2
There are three key principles that you need to keep in mind about repairing (and re-levelling) TC1 and TC2 foundations…
- Often there is little difference between repair strategies in TC1 and TC2
- Repair strategies for both Technical Categories rely on the outcome of a shallow ground investigation
- Engineering sign-off is always necessary for TC2, and also in all cases of specific engineering design
What are the key principles?
- Often there is little difference between repair strategies in TC1 and TC2
- Repair strategies for both Technical Categories rely on the outcome of a shallow ground investigation
- Engineering sign-off is always necessary for TC2, and also in all cases of specific engineering design
Foundation types
Helpful information about repairing Type A
Section 4.2 (PDF 3.75MB) of the Guidance
Figure 5a (PDF 2.68MB) of the Below-Floor Work booklet
Helpful information about repairing Type B
Section 4.2 (PDF 3.75MB) of the Guidance
Figures 4.2 and 4.2a (PDF 3.75MB) of the Guidance
Appendix A1 (PDF 3.75MB) of the Guidance
Figure 6 and Information in the Below-Floor Work booklet (PDF 2.68MB)
Helpful information about replacing Type B
Section 5 (PDF 3.75MB) and Figure 4.2a (PDF 3.75MB)
Helpful information about repairing Type C
Section 4.2 (PDF 3.75MB) of the Guidance
Appendix A1 (PDF 3.75MB) of the Guidance
Appendix A4 (PDF 3.75MB) of the Guidance
Helpful links & info
Do I need a building consent for repairing or re-levelling a foundation?
Repairs or replacement of structural components will need a building consent, however, some minor structural repairs may not need a building consent. Check with the local building consent authority and Section 8.2.4 (PDF 955KB) of the Guidance and in the Below-Floor Work booklet (PDF 2.68MB).
Do I need engineering input for ground testing?
Shallow ground testing is required for all foundations in TC1 and TC2. Chartered Professional Engineer (CPEng) sign-off is required for ground testing when repairing foundations in TC2, and also in TC1 for ground <300kPa.
Refer to Figure 4.1 (PDF 3.75MB) and Figure 4.3 (PDF 3.75MB) of the Guidance respectively.
Where can I get copies of the Guidance?
The Guidance is available online via the building.govt.nz website.
5. Rebuilding TC1 and TC2 Foundations
- Welcome to Topic 5, which is about rebuilding TC1 and TC2 foundations
- In this topic we will focus on where to find information about rebuilding foundations in TC1 and TC2
- Welcome to Graeme Beattie, Professional Engineer and Advisor to MBIE…
Here’s how to get the best from Topic 5:
- Read the Key Principles
- Click on the diagram to get further information about rebuilding TC1 and TC2 foundations
- Click on the questions (bottom right of this screen) to find out more
…and don’t forget, “Build it right, Canterbury!”
- When foundations are badly damaged, a rebuild is likely.
- So, what exactly do we mean by a ‘rebuild’? …a rebuild is a total replacement of the foundations
- New foundation designs have been developed for TC2 to cope with possible future ground movement
- These foundation designs can also be used in TC1 if the ground conditions are poor
- In this Topic, we’ll cover ways to rebuild foundations in TC1 & TC2
There are two key principles that you need to keep in mind about rebuilding TC1 and TC2 foundations…
- Firstly, the aim of rebuilding is to provide foundations that are resilient to ground movement in future earthquakes
- Secondly, options for building in TC1 & TC2 will depend on the interplay of five elements… the TC, the cladding weights, the floor plan shape, the foundation type, and the ground conditions
What are the key principles?
- The aim of rebuilding is to provide foundations that are resilient to ground movement in future earthquakes
- Options for building in TC1 & TC2 will depend on the interplay of five elements: TC, cladding weights (roof and wall), plan shape, foundations and ground conditions
What you should consider
Plan Shape
Simple plan shapes are preferred in TC2. There are four simple floor plan layouts: Rectangular, L-shaped, T-shaped and Boomerang-shaped. See Section 5.3 (PDF 3.75MB) p 5.7 of the Guidance only.
Cladding
When we refer to cladding, it incorporates both wall and roof claddings. There are light, medium and heavy wall claddings, and light or heavy roof claddings.
For more detailed information, see the Guidance — Section 7.9 (PDF 3.75MB) and Table 7.2 (PDF 3.75MB).
You can also find further information on Maximum cladding weights Table (PDF 2.68MB) p 34-35 and Light or medium weight claddings (PDF 2.68MB) in the Below-Floor Work booklet.
Foundations and Ground
For new foundations in TC1 and TC2, refer to Section 5 (PDF 3.75MB) p 5.1—5.18 of the Guidance. For TC1, normal NZS3604 foundations apply. For TC2, there are various foundation options available, depending on ground conditions. Foundation options are outlined in Figures 5.1 and 5.2 (PDF 3.75MB) p 5.2–5.3 of the Guidance, and in the Below-Floor Work booklet (PDF 2.68MB) p 32-33.
Technical Categories (TC)
For more information about the Technical Categories go to Topic 2.
Helpful links & info
Do I need a building consent for rebuilding a foundation?
All new structural work requires a consent except for minor work covered by Schedule 1. See also Below-Floor Work booklet (PDF 2.68MB), first bullet point.
Are there any restrictions to the design of the building, apart from foundations?
Yes — For TC1, normal NZS3604 conditions apply. For TC2, there are restrictions for cladding weights and floor plan shapes, depending on foundation option selected — see Table 7.2 (PDF 3.75MB) p 7.10 of the Guidance.
When is ground testing with engineering input required?
Shallow ground testing is required for all new foundations (partial or full replacement) in TC1 and TC2. Chartered Professional Engineer sign off is required for ground testing when rebuilding foundations in TC2, and also in TC1 for ground <300kPa. — refer to Figure 5.1 (PDF 3.75MB) and Figure 5.2 (PDF 3.75MB) p 5.2 and 5.3 of the Guidance respectively.
What are ‘enhanced’ foundations?
Enhanced foundations options comprise either a stiffened concrete slab Figures 5.5-5.11 p 5.8-5.11 or a perimeter foundation wall Section 5.3.2 and Figure 4.2a (PDF 3.75MB) of the Guidance.
What if I am rebuilding a foundation for a stand-alone (detached) garage or other out-building?
Rebuild the foundation as required for the next lowest Technical Category refer Below-Floor Work booklet (PDF 2.68MB) and Information Sheet.
Where can I get copies of the Guidance?
The Guidance is available online via the building.govt.nz website.
6. Dealing with TC3 Foundations
- Welcome to Topic 6, which is about dealing with TC3 foundations
- In this topic we will focus on where to find information about repairing and rebuilding foundations in TC3
- Welcome to Graeme Beattie, Professional Engineer and Advisor to MBIE…
Here’s how to get the best from Topic 6:
- Read the Key Principles
- Click on the diagram to get further information about dealing with foundations in TC3
- Click on the questions (bottom right of this screen) to find out more
…and don’t forget, “Build it right, Canterbury!”
- The decisions in TC3 are more complex
- And you’ll need to involve a professional engineer for repairs and rebuilds
- In TC3 there is a higher probability of land damage in future large earthquakes
- Several new foundation types have been developed especially for TC3 sites, but it’s important to know the limits for each of them
- In TC3, don’t mix foundation solutions – this could lead to incompatible performance
- In this Topic, we’ll cover ways to both repair and rebuild foundations in TC3
There are four key principles that you need to keep in mind about repairing and rebuilding TC3 foundations…
- TC3 foundation options take into account the increased likelihood of future ground movement, particularly lateral spread
- Foundation damage in TC3 requires professional engineering input to find a suitable repair or rebuild solution
- Lightweight cladding materials are preferred for all foundation types in TC3
- Keep in mind the idea of ‘Readily Repairable’ – base designs on minimising future damage
What are the key principles?
- TC3 foundation options take into account the increased likelihood of future ground movement, particularly lateral spread
- Foundation damage in TC3 requires professional engineering input to find a suitable repair or rebuild solution
- Lightweight cladding materials are preferred for all foundation types in TC3
- Keep in mind the idea of ‘Readily Repairable’ — base designs on minimising future damage
Dealing with TC3 Foundations
Plan Shape
Regular structural plan shapes are important for surface structures in TC3. Supplementary Guidance provides more information about this.
Regular plan shapes are also required for site ground improvement.
Cladding
When we refer to cladding, it incorporates both wall claddings and roof claddings. There are light, medium and heavy wall claddings, and light or heavy roof claddings. See Section 7.9 (PDF 3.75MB) and Table 7.2 (PDF 3.75MB) of the Guidance.
Cladding weight is an important consideration for dwellings in TC3. Find out more about the effect of claddings on foundation designs (PDF 2.61MB) and see Table 15.1 (PDF 2.61MB) and Table 7.2 (PDF 3.75MB) of the Guidance.
Find further information on Maximum cladding weights table (PDF 2.68MB) and Light or medium weight claddings (PDF 2.68MB) in the Below-Floor Work booklet.
Foundations and Ground
To learn about repairing foundations in TC3, see Section 14 (PDF 2.61MB).
For further information about assessment for repairs in TC3, go to Topic 3 — Assessment.
To learn about rebuilding foundations in TC3, see Section 15 (PDF 2.61MB).
There are three main approaches for rebuilding a foundation in TC3 — 1) Deep piles, 2) Site Ground Improvement and 3) Surface Structures with shallow foundations.
The Guidance describes eight deep pile types that can be used in TC3. Deep piles provide the greatest flexibility for the superstructure configuration and weight, but are restricted to ground with limited lateral spread. More information on deep pile types and associated floor options can be found Section 15.2 (PDF 2.61MB) of the Guidance and in Pile design options supplementary guidance (PDF 552KB).
Site ground improvement is divided into shallow ground treatment (PDF 2.61MB) or deep foundation treatments (PDF 2.61MB).
Table 15.4 (PDF 2.61MB) has more information on foundation treatments.
For surface structures there are three foundation types (PDF 2.61MB). An advantage of surface structures is that they allow for future re-levelling if necessary.
For information about assessment for rebuilding foundations in TC3, go to Topic 3 — Assessment.
Technical Categories (TC)
To learn about the complexities of TC3, See Section 11.1 (PDF 2.61MB). For further information about Technical Categories, go to Topic 2.
Helpful links & info
Are there restrictions in selecting a foundation type when rebuilding on my TC3 site?
Yes, depending on the assessed ground conditions, the Chartered Professional Engineer will select the type of foundation best suited for your site (PDF 2.61MB).
Do I need a building consent for repairing or rebuilding a foundation in TC3?
All new structural work requires a consent. Some minor repairs may not need a building consent. Check with the local building authority and see Appendix C1 (PDF 2.61MB) of the Guidance, and the Below-Floor Work booklet (PDF 2.68MB).
When do I need deep ground assessment (as opposed to shallow) in TC3?
Deep ground assessment is required for all rebuild foundation options in TC3. For repairing foundations, the type of ground assessment will be determined by a Chartered Professional Engineer (CPEng) — see Figures 14.1 and 14.2 (PDF 2.61MB).
What about mixed foundation types in TC3?
The Guidance does not recommend mixing foundation types — refer Section 11.2 (PDF 2.61MB) item 7.
What if I am repairing or rebuilding a foundation for a stand-alone (detached) garage or other out-building in TC3?
Foundation repairs for stand-alone garages and out-buildings are not considered in the Guidance, however when rebuilding foundations for out-buildings in TC3, apply the requirements for the next lowest Technical Category refer Below-Floor Work booklet (PDF 2.68MB) and Information Sheet.
Where can I get copies of the Guidance?
The Guidance is available online via the building.govt.nz website.
