The Christchurch earthquakes on September 4 and Boxing Day 2010 did not significantly weaken the resistance of three buildings that failed in the February 22 quake, an expert report has found.

The report, prepared on behalf of the Department of Building and Housing for the use of the Canterbury Earthquakes Royal Commission, was released last week, when the royal commission was holding public hearings into major building failures (See other story).

The experts say the failure of the Pyne Gould building, the Hotel Grand Chancellor and the Forsyth Barr Building reflected older design standards and say today’s standards need to be strengthened further.

They say more needs to be done to educate New Zealanders about the risk from older buildings.

A major recommendation says owners of buildings constructed prior to 1992 need to check that stairs are designed to accommodate earthquake movement. The internal stairs in the 18-storey Forsyth Barr Building – the only emergency escape route – collapsed because the shaking on February 22 exceeded the design capacity provided for the stairs to move in an earthquake.

It is possible that the gaps allowing for movement had been filled with material such as debris, mortar or polystyrene, the report says.

The shaking on February 22, while relatively short, was significantly greater than allowed for in the design of new buildings.

The expert panel makes a number of recommendations to strengthen buildings and prevent stairs collapsing before tenants can get out.