Building Controls Update No. 114: Immediate changes to sesimicity and foundation details for Christchurch

19 May 2011

The Department of Building and Housing is making immediate changes to the Building Code's supporting documents for Structure, to increase the seismic hazard factor for Christchurch and to require stronger foundations for buildings in that area.

The changes take effect on 19 May 2011, so that Christchurch building owners can rebuild or repair with certainty as quickly as possible.

Why make the changes?

The 2010/11 Canterbury earthquakes have increased the seismic risk for Christchurch over the next few decades. Based on new knowledge about this risk, seismologists and structural engineers who reported to the Department, agree that the seismic hazard factor for Christchurch should be raised from 0.22 to 0.3.

What are the changes?

The documents being changed are the Structure Verification Method B1/VM1 and the Structure Acceptable Solutions, B1/AS1 and B1/AS3. The immediate changes will:

• increase the seismic hazard factor for Christchurch from 0.22 to 0.3
• strengthen the definition of 'good ground' and require concrete-slab foundations to have reinforcing
• clarify that foundations on ground that is prone either to liquefaction or lateral spread should be specially designed.

What areas are affected by the changes?

The changes take effect in the local Councils areas of Christchurch City, Waimakariri and Selwyn. However, for those parts of Waimakariri and Selwyn District Councils that already have a seismic hazard factor greater than 0.3, there is no reduction to that hazard factor.

Where can I obtain further information on the changes?

The new B1 Compliance Document, containing the amended Verification Method and Acceptable Solutions, will be available from Thursday, 19 May, at: www.dbh.govt.nz/compliance-documents.

The Department has produced an information sheet on the changes which is also available on the Department's website from Thursday, 19 May. Please note that designers will need to consult the Building Code documents.

Proposals to change the New Zealand Building Code

The Department plans to consult on proposals to make the New Zealand Building Code clearer and more specific about risk management for earthquakes and other structural hazards in June/July 2011. At the same time, the Department will consult on these immediate changes already made to the Building Code's supporting documents for Structure, in accordance with section 30 of the Building Act 2004.