A lawyer acting for the structural designer of the CTV building has downplayed failures attributed his client at a royal commission hearing.
Hugh Rennie QC, acting for Dr Alan Reay of Alan Reay Consultants, said the "exceptional and unexpected" effects of the earthquakes that destroyed the building in February 2011, killing 115 people, were not anticipated by engineers who designed buildings in Christchurch.
He said that knowledge about earthquake design was less advanced than now, witnesses were no longer alive, and many documents were not available to give a full picture of the background to the construction of the building.
Mr Rennie also rejected any notion that Dr Reay had influenced city council planners.
Had the building been managed better during the course of the earthquakes the fatalities might not have occurred, Mr Rennie said.
He said the property manager failed to act on complaints of tenants and assessments by engineers.
Stephen Mills, the lawyer assisting the commission, said serious problems were known by the designers in 1990, five years after construction of the building, but none of the parties who knew told Christchurch City Council.
Though Dr Reay had noted there were a number of technical reasons for the building's failure, Mr Mills said the principal failings happened during the design work, led by David Harding and carried out by Dr Reay's firm.
"The decisions they made about the structural design of the building are the primary cause of the CTV building collapse," Mr Mills said.
"It was Dr Reay's decision to give Mr David Harding the virtually sole responsibility for carrying out the structural design for the CTV building, in circumstances where he was on any objective view not competent to do this.
"Dr Reay then made a deliberate decision to provide no active supervision or mentoring for Mr Harding in the work he was doing."
The Canterbury Earthquakes Royal Commission has been hearing closing submissions on Thursday into the building's collapse.