Structural design decisions were the primary cause of the CTV building’s collapse in last year’s February 22 Christchurch earthquake, according to counsel assisting the Earthquakes Royal Commission.

Stephen Mills QC told the hearing that in critical respects the building, designed by Alan Reay Consultants, was not code-compliant and was dangerously vulnerable to any earthquake that took the building beyond its “elastic response state” – its ability to move in a quake.

He says the tower was the only building in Christchurch designed to the 1982 and 1984 codes that suffered a “complete and catastrophic collapse” that day. The collapse claimed 115 lives.

Mr Mills says principal structural designer David Harding was not competent enough to take responsibility for the design, and his employer, Dr Reay, should have provided supervision.

He says eight weeks of hearings have revealed failings and weaknesses at a number of levels, including regulatory processes at Christchurch City Council.

“What has become apparent in the course of this hearing is that much more is involved in the collapse of the CTV building than the single event that occurred on February 22 2011,” Mr Mills told the commission.

Counsel for Dr Reay, Hugh Rennie QC, told the commission there have been major advances in earthquake knowledge, building design and construction since the CTV tower was finished in 1987.

The Christchurch earthquakes “were of such a nature, location, force and direction as to impose demands on Christchurch buildings that had not been foreseen”, he says.

Mr Rennie says Dr Reay and others in the design company considered Mr Harding competent for the job. He says the building’s location may have made it relatively earthquake-prone.