One of the most important reports in last year's Christchurch earthquake, a report looking into the CTV the collapsed building in which 115 died, has been released. Families of the casualties have been briefed of the cause of the collapse - inflexible and brittle columns, among other general findings.

The Department of Building and Housing (DBH) has found the six-storey building fell short of the required building standards when constructed in 1986, the New Zealand Herald reported.

The report's bottomline is that the CTV building failed to meet the standards that could have prevented the collapse on the day of the quake.

Fairfax reported the three "critical" factors in the collapse according to the report: the intense horizontal ground shaking; brittle columns; and the asymmetrical layout of structural walls, causing the building to twist in the quake and place extra strain on the columns. Also, concrete in the columns was significantly weaker than expected.

The Herald spoke to Karen Bishop, whose son Andrew, 33, died in the collapse, and she was appalled to find out that the building was not up to standard.

"Someone has to be answerable for this. For God's sake, it killed 115 people and it should never have happened," Ms. Bishop said.

Fairfax NZ spoke to Mike Didham, whose wife Joanna worked for CTV, and he expressed relief over finding some answers.

"I always wanted to know why that one. It's just unlucky that our people were in it," Mr. Didham said.

The department has endorsed the report to police and the Institution of Professional Engineers. Both bodies are considering further action.

However, Alan Reay Consultants Ltd (ARCL), which designed the CTV building, disputed several of the report's findings.

ARCL Director Alan Reay said on Thursday that the report was technically inadequate.

"Some of the assumptions made in the reports are highly questionable. As a consequence, the report's findings are not conclusive. In fact, in many areas they may be flawed," he said.

But investigation deputy Nigel Priestley, a former professor of Structural Engineering at the University of California and former senior lecturer at Canterbury University, told Radio New Zealand the report provided all the necessary information.

"It's been a very thorough piece of work, and the causes of failure as defined in the report are correct, and well researched, and fully justified by the analyses that have been done," he said.

Police Assistant Commissioner Malcolm Burgess said police would be seeking legal advice to determine the next step.