Computer disks containing vital information on the Canterbury Television building may have been dumped after the February 2011 earthquake, an inquiry has heard.
Alan Reay, the engineer whose company designed the building, yesterday told a royal commission hearing that not all the CTV paperwork had been kept.
The commission lawyer for victims' families, Marcus Elliot, asked Reay why key documents requested by the commission had not been provided.
The commission was particularly interested in his firm's response to a 1986 Christchurch City Council letter requesting further information for the code of compliance application, which could not be located.
All documents on the file had been provided, Reay said.
"Some of [the CTV file] was retained. What isn't retained we can't be 100 per cent sure of," he said.
The information provided to the commission was printed from computer disks.
Reay was asked to produce the disks, but said they were disposed of after being transferred to a hard drive.
Elliot asked: "Is it your evidence that after February 2011 you disposed of a disk containing documents relevant to the CTV building?"
Reay thought the disks had been disposed of, but he would "have to check".
The was no legal obligation to retain job files, he said.
Some company files held in an off-site storage facility had been ruined by a leaking roof, Reay said.
Documents later supplied to the commission were found in a storage box marked "miscellaneous".
Reay said he looked for more documents but found none. "I haven't been able to find any and I don't think there are any," he said.
Staff could have removed documents from the file and not returned them.
"Everyone in the office has access to files to look for whatever they choose. If someone chose to get information out of that file, they may not have put that information back," Reay said.
The commission heard that simulating the effects earthquakes had on the CTV building would have cost "several million" dollars.
Reay said last week that he was "dissatisfied" with a Building and Housing Department report on why the building collapsed in the February 22, 2011, quake.
More experiments, such as a reduced-scale model of the CTV building being tested on a shake table, should have been done, he said.
Under questioning from commissioner Richard Fenwick yesterday, Reay said the cost of that testing would have been "several million" dollars.
Commission chairman Justice Mark Cooper asked why Reay had not provided calculations or studied the building plans when he presented five collapse scenarios in response to the department's findings.
"It could be that some of them aren't significant in relation to the collapse of the building. In preparing a report such as the DBH prepared, I would have expected some investigation and analysis of those [alternative scenarios].""I was putting forward scenarios I considered hadn't been considered," Reay said.