Building Controls Update No 124 confirmation of May 2011 changes to seismicity and foundation detail

Issue 34 – December 2011

The Chief Executive of the Department of Building and Housing (the Department) has confirmed the urgent changes made to the Building Code documents for Structure (B1) on 19 May 2011. Read the reasons for this decision ( on the Department's website.

The changes were made urgently in May so that Christchurch building owners could commence rebuilding or repair work with certainty as quickly as possible. Consultation, required after urgent changes by the Building Act 2004, showed strong support for the 19 May amendment. The Department thanks all those who took the time to make submissions.

Key changes

The key changes made for the Canterbury earthquake region on 19 May 2011 were as follows.

  • Increased the seismic hazard factor for the Canterbury earthquake region from 0.22 to 0.3 minimum.
  • Strengthened the definition of 'good ground'.
  • Required concrete slabs-on-ground to be reinforced with ductile steel mesh, which is tied to perimeter foundation reinforcement.
  • Made clear that foundations should be specially designed on ground that is prone to liquefaction or lateral spread.

The changes apply to the Canterbury earthquake region, defined by the boundaries of the local Council areas of Christchurch City, Waimakariri District, and Selwyn District. However, for those parts of Waimakariri and Selwyn District Councils that already had a seismic hazard factor greater than 0.3, there was no reduction to that hazard factor.

The Canterbury changes took effect on 19 May 2011.

Information supplied by Department of Building and Housing, 17 November 2011.

Published in building.