Media release: Updated guidance for the repair and reconstruction of homes in Canterbury published
9 December 2011
The Department of Building and Housing (the Department) has today published updated guidance on the repair and reconstruction of houses in earthquake-affected areas of Canterbury.
The Department’s Revised guidance on repairing and rebuilding houses affected by the Canterbury earthquake sequence includes information for the repair and reconstruction of homes, including foundations, in green zone technical categories 1 and 2 (TC1 and TC2).
Department of Building and Housing Chief Executive Katrina Bach says the updated guidance will allow homeowners with damaged properties in the residential green zone to get on with the process of repairing or rebuilding their homes with greater confidence.
“The document forms part of the Government’s support for long-term recovery in Canterbury. It gives robust and well-balanced engineering solutions that will reduce the risk of injury to people and damage to homes in future earthquakes.”
The revised document reflects new scientific and geotechnical information and knowledge about the impact of earthquakes and the effects of liquefaction on residential dwellings.
It includes useful information on repairs to foundations and new foundations in TC1 and TC2, assessments of retaining walls for hillside properties, chimney repairs and repairs to house superstructures, pole frame houses and masonry walls.
The guidance also applies to repairs to homes in green zone technical category 3 (TC3) that do not involve foundations. Homes in TC3 with foundation damage requiring structural repair will need site-specific geotechnical investigation and specific engineering foundation design. Further investigation is being undertaken to inform the development of suitable foundation solutions for TC3.
The Department’s Revised guidance on repairing and rebuilding houses affected by the Canterbury earthquake sequence supersedes the guidance issued by the Department in December 2010 in response to the 4 September 2010 Canterbury earthquake.
The guidance document can be downloaded from the Department’s website.
For further information contact Sarah Morton, Senior Advisor Sector Engagement and Communications, phone 04 817 4266 or 027 501 5829.
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Questions and answers
1. Who was involved in developing the guidance?
The Department of Building and Housing's guidance has been developed by the Department’s Engineering Advisory Group.
This group comprises experienced practitioners, including practitioners from the Department, BRANZ, the New Zealand Society for Earthquake Engineering, the Structural Engineering Society of New Zealand, the New Zealand Geotechnical Society, Tonkin & Taylor, the Earthquake Commission (EQC) and others. There has also been significant input at various stages of the process from international experts.
2. Why has the December 2010 guidance been revised?
The Department’s December 2010 Guidance on house repairs and reconstruction following the Canterbury earthquake has been revised to reflect new scientific and geotechnical information and knowledge about the impact of earthquakes and the effects of liquefaction of residential dwellings.
The Department’s revised guidance includes information about the three new technical categories for foundation systems (TC1, TC2 and TC3). The technical categories are an integral part of the Department’s revised guidance.
Homeowners who carry out their repairs and reconstruction work using the Department’s revised guidance will meet the requirements of the Building Code.
All building work in New Zealand must meet the requirements of the Building Code.
3. Who is the guidance for?
The Department’s Revised guidance on repairing and rebuilding houses affected by the Canterbury earthquake sequence is intended for the engineering design, construction and insurance sectors, local authorities, and their professional advisors and contractors.
4. Does the guidance apply to all homes in the green zone?
The Department’s Revised guidance on repairing and rebuilding houses affected by the Canterbury earthquake sequence includes information for the repair and reconstruction of houses, including repairs to foundations, in TC1 and TC2.
The guidance also applies to houses in TC3 that do not require structural repairs to foundations.
Homes in TC3 with foundation damage requiring structural repair will need site-specific geotechnical investigation and specific engineering foundation design.
5. Is the Department developing guidance for repairs to foundations in TC3?
Yes, the Department of Building and Housing is conducting a research trial to test a range of other innovative foundation solutions for houses in TC3. It will develop further guidance when it has completed the trial.
Homeowners in TC3 can proceed with repairs to foundations now but they will require site-specific geotechnical investigation and specific engineering foundation design. Site-specific geotechnical investigation will help your designer identify the best foundation solution for your property.
6. Does this guidance supersede the Department’s December 2010 guidance?
Yes, the Department’s Revised guidance on repairing and rebuilding houses affected by the Canterbury earthquake sequence supersedes the guidance published in December 2010 in response to the Canterbury earthquake of 4 September 2010.
7. If I follow the Department’s guidance will I meet Building Code requirements?
Yes, the Department’s guidance encourages a consistent approach to repair and rebuilding that minimises the individual investigation and design effort required for each property. It provides solutions and construction methods that will meet the requirements of the Building Act and the Building Code.
8. What if I’ve already completed my repairs using the Department’s December 2010 guidance?
If you completed your repairs following the Department’s December 2010 guidance and meet the requirements of your building consent at the time it was issued, you don’t need to take any further action.
Your code compliance certificate (issued on completion of your building work by your council) demonstrates that your building work meets the requirements of your building consent.
If you completed your repairs in accordance with the Department's December 2010 guidance and the work was exempt (i.e, you did not require a building consent), you don’t need to take any further action.
The Revised guidance on repairing and rebuilding houses affected by the Canterbury earthquake sequence is generally consistent with the guidance issued by the Department in December 2010.
The December 2010 guidance has been updated to reflect new knowledge about the performance of buildings during the earthquakes. The revised guidance covers a wider range of issues, including the assessment of retaining walls in the Port Hills and repairs to concrete slab foundations.
9. What if I’ve already started my repairs using the Department’s December 2010 guidance?
If you have been issued a building consent notice and you have already commenced your repairs following the Department’s December 2010 guidance you do not need to take any further action. You can continue to carry out your repairs in accordance with the requirements of your building consent.
If you have determined that your repairs are exempt (i.e, you do not require a building consent) and you have started those repairs, the Department recommends that you refer to its revised guidance and compare your proposed repairs with the solutions provided in that document.
The Revised guidance on repairing and rebuilding houses affected by the Canterbury earthquake sequence is generally consistent with the guidance issued by the Department in December 2010.
The December 2010 guidance has been updated to reflect new knowledge about the performance of buildings during the earthquakes. The December 2011 guidance covers a wider range of issues, including the assessment of retaining walls in the Port Hills and repairs to concrete slab foundations.
10. My house has been classified TC3 but I have not had significant liquefaction. Will it be re-categorised?
The technical categories only apply if you have foundation damage. The technical categories are based on the best available geotechnical information. It has not been possible in the time since 13 June 2011 and the finalisation of foundation guidelines to complete individual land assessments. It was important to enable homeowners in the green zone to progress their repairs as quickly as possible.
Site-specific geotechnical investigation will help your designer/engineer identify the best foundation system for your property. Geotechnical engineers may recommend that a TC2 type foundation solution is able to be used for many of the properties in TC3. The appropriateness of this will only be identified once the individual site geotechnical assessment is undertaken.
You will need to provide the geotechnical evidence to your council when you apply for a building consent.
The geotechnical evidence you supply will be collected in a database and over time the technical category boundaries will be adjusted to reflect the improved understanding of Canterbury soil conditions.