The principal of the firm that designed the CTV building in Christchurch today denied any involvement in designing the building that collapsed in last year's February earthquake, killing 115 people.

Alan Reay, who heads Alan Reay Consultants Ltd, told the royal commission hearing into the Canterbury earthquakes that responsibility for the building design rested "entirely" with David Harding, who was employed as a structural engineer.

Dr Reay said Mr Harding joined his firm in late 1985 and took over responsibility for the CTV building project.

"At the time I was fully engaged on other projects," he said.


"Mr David Harding took control."

"Despite what Mr Harding says, I was not involved in the design."

Dr Reay said Mr Harding was a qualified structural engineer with experience in the construction of concrete buildings and considered himself capable to work on the CTV building design.

He was expected to seek advice if needed.

At the time the CTV building was under construction Mr Harding was "more familiar with the Concrete Code than I was," Dr Reay said.

"He was focused on the design of significant concrete structures."

Dr Reay said he was unable to recall if any computer modelling had been done in designing the CTV building.

As the design engineer, Mr Harding would have been responsible for ensuring the building fully complied with all codes current at the time.

Mr Harding told the hearing earlier today that he accepted an offer to work at the consultancy responsible for designing the six-storey office block because it was "an opportunity to do multi-level design".

"That was the reason I went," he told counsel assisting the commission Stephen Mills QC.

Mr Harding said he'd worked for Alan Reay previously and while he had earlier expressed concerns about the "culture" at the consultancy, he felt "sufficiently comfortable" to return. He worked on the design between 1984 and 1985.

He disagreed with a suggestion from Mr Mills that the "bigger lure" was the possibility of gaining an associateship at the consultancy.

While the prospect of being made an associate had been discussed with Dr Reay, it was not the "principal reason" he accepted the position.

Mr Harding said Dr Reay mentioned in a telephone call that someone in the firm was leaving or about to leave and he wanted him to replace that person.

He said Dr Reay told him he had multi-storey building design work coming up and asked him to fill the gap at the consultancy with Dr Reay in a supervisory role.

Earlier, Mr Harding told the hearing he had no experience with multi-level building and had been engaged mainly on council roading work for the previous five years.

He said he would not have taken on the CTV building if he'd been in practice on his own, but felt he was "up to the task" given he would be supervised and would have the benefit of "accumulated knowledge" from others in the firm.

To Mr Mills, he agreed that Dr Reay's oversight gave him a "level of comfort". It was his interpretation that Dr Reay's involvement was principally in checking his work.

"That was my understanding at the time."

Mr Harding said several key design components in the building had already been decided when the design was handed to him.

The commission is trying to establish why the concrete office block failed catastrophically in the magnitude-6.3 quake.

It is expected to deliver its report in November.