Questions and answers - Green TC2 (yellow)

Technical Category 2 (yellow)

What do I need to do to ensure my repairs meet Building Code requirements?

Homeowners whose land is in TC2 can get on with rebuilding their homes with confidence. The only further site-specific geotechnical investigation required is the simple shallow soil strength testing which is standard for all homes.

New foundations

If your home is in TC2 and you are rebuilding foundations the Department of Building and Housing recommends that you use:

  • Standard (NZS3604) piled foundations for houses that:
    • Are built of lightweight materials (not masonry or brick veneer). For example tin, not tiled, roofs and lightweight cladding such as weatherboards; and
    • Have timber floors instead of concrete floors
  • Or enhanced slabs (more robust foundations) such as those outlined in the Department of Building and Housing’s December 2010 Guidance on house repairs and reconstruction following the Canterbury earthquake.

Repairs to foundations

If you are carrying out repairs to foundations or other areas of you home these should be carried out in accordance with the Department of Building and Housing’s 2010 Guidance on house repairs and reconstruction following the Canterbury earthquake

The Guidance on house repairs and reconstruction following the Canterbury earthquake document is being updated. A summary of the update, the 2010 guidance and other documents are available on the MBIE, Building and Housing Group website.

Talk to your builder or project management office about the requirements of this guidance and the Building Code.

How much are repairs to foundations likely to cost?

The average additional cost for homeowners in Technical Category 2 with foundations that need to be repaired or rebuilt due to earthquake damage is expected to be around $5,000. However, depending on site circumstances costs may range from no additional cost to around $10,000.

What if my house wasn’t damaged in the earthquakes and is in TC2?

The technical categories only apply to houses that require their foundations to be repaired or rebuilt due to damage from the earthquakes. If your house was not damaged by the earthquakes then you will not need to upgrade your foundations.

Where can I find more information?

More information is available on the MBIE, Building and Housing Group website.

What is the difference between the technical categories?

Land in the green zone has been divided into three technical categories. These categories describe how the land is expected to perform in future earthquakes.

Technical category 1 (TC1) - grey

Future land damage from liquefaction is unlikely. You can use standard foundations for concrete slabs or timber floors. Foundation requirements changed in 2011 and information is available on the MBIE, Building and Housing Group website.

Technical category 2 (TC2) - yellow

Minor to moderate land damage from liquefaction is possible in future significant earthquakes.

You can use standard timber piled foundations for houses with lightweight cladding and roofing and suspended timber floors or enhanced concrete foundations – i.e. more robust floor slabs that better tie the structure together as outlined in the Department of Building and Housing 2010 Guidance on house repairs and reconstruction following the Canterbury earthquake. More information is available on the on the MBIE, Building and Housing Group website.

Technical category 3 (TC3) - blue

Moderate to significant land damage from liquefaction is possible in future significant earthquakes. Site-specific geotechnical investigation and specific engineering foundation design is required.

Related information

Residential green zone technical categories