A detailed assessment of the stairs in Christchurch's damaged Forsyth Barr building was recommended after the September 2010 earthquake but had not started when they failed in February.
The 18-storey, central-city building was a high-profile casualty of February's earthquake, with office workers abseiling down the face of the building after the stairwells collapsed – one side up to level 13 and the other up to level 15.
A report into the collapse, released last week, said an initial "rapid assessment" cleared the building for normal use after the September shake but suggested there be a detailed investigation of the stairs.
The report, prepared for the Department of Building and Housing (DBH), said that assessment was never done.
Structural engineering firm Holmes Consulting prepared instructions for the repair of "cracked structural elements" in November.
The DBH report said: "The engineers have advised that they were told to exclude stairs from consideration."
Holmes Consulting managing director Bruce Black said by the time his company made its first visit to the building on November 1 last year, work on repairing the stairs was already under way.
Peter Rae, a director of 764 Colombo Street Ltd, which owns the Forsyth Barr building, said a quote for more extensive repair work on the stairs had been accepted by February 22, but work had not started.
It was the project manager's intention for Holmes Consulting, the engineers for the tower's construction in 1988, to undertake a detailed assessment of the stairs before the work began, he said.
Asked if, in hindsight, more should have been done to the stairs, Rae said: "Our building managers and project management team believed they took the appropriate steps post-September, and I have certainly asked that question."
While the separations at the base of all stairs – allowing them to move during a shake – could have been filled with construction debris, the report said the gaps were too small for the shaking experienced on February 22.The DBH report said damage during earthquakes on September 4 and December 26 last year "is not considered to have significantly weakened the stairs".
"Our analyses predict that the stairs would have collapsed even if the gaps were clear of obstructions."
The DBH report was written by engineering firm Beca Carter Hollings & Ferner, which undertook the Forsyth Barr building's rapid assessment after September last year.
Questions were raised last Friday about Beca's potential conflict of interest. Beca stated in the DBH report that it was working for the property management company and Holmes was working for the building owner.
Rae dismissed that notion, saying: "Anybody acting for the building manager is acting for the owner."
DBH building quality deputy chief executive David Kelly said there was no evidence that earlier damage to the stairs resulted in the final collapse.
Beca's technical director of earthquake engineering, Richard Sharpe, who helped in the Forsyth Barr investigation, said the report was factual and did not discuss potential culpability.
No decision has been made about the building's future.
Rae said a soon-to-be-built temporary external stairwell would allow a more detailed assessment of structure and repair costs.
Rae had an office on the 11th floor and a crane helped him out more than four hours after the February earthquake.
He initially feared the worst and was surprised no-one had been caught by the collapsing stairwell.
Urban Search and Rescue gave the building the all-clear a week later.