Crucial files documenting how the CTV building was built could have been destroyed after the February 22 earthquake, a hearing was told today.
The boss of the engineering firm that designed the doomed Christchurch office block thinks that computer disks holding documents relating to the building may have been "disposed of" after the disaster.
Alan Reay, director of Alan Reay Consultants Ltd, was trying to explain to the royal commission hearing today what happened to a missing portion of the CTV building file, which could have explained if the building was code compliant when it was built.
The CTV building collapsed in the magnitude-6.3 February 22 quake, killing 115 people.
Dr Reay's firm designed the six-storey building in the mid-1980s and files would have been kept once the job was done.
But a portion of the file is missing, and the Canterbury Earthquakes Royal Commission hearing asked today where it may have gone.
Under questioning from counsel assisting the commission Marcus Elliott, Mr Reay said he thinks a staff member may have opened the file, and not put it back, or at least not put it back in the right place.
Or it could have been one of the files kept in a lock-up garage which went mouldy after "about 10 years", or was mixed up with another building's file and had not yet been found.
But one of the most alarming possible explanations for the "lost" files is that the disk it was on was destroyed after the February quake.
"We don't have disks any more. In the February earthquake, everything ended up in a shambles so what we've done since is put everything on a hard drive," Dr Reay told the hearing, which today (Monday) entered its fourth week.
Once the information was taken off the disks, he thought they were then disposed of.
The missing CTV files have never been found, and Dr Reay said he had searched his entire office without luck.
He accepted it was important for the royal commission to have all relevant documents before them when trying to establish how the building failed so catastrophically.
No disk had been given to the royal commission as part of his firm's evidence, but Dr Reay vowed to check what happened to the CTV disk.
The missing documents meant he couldn't categorically state that the concrete structure complied with the building regulations of the day.
Dr Reay earlier criticised the Department of Building and Housing report into the CTV collapse as being "technically inadequate".
He told the royal commission that people deserved to know all aspects of why the building failed and said further full scale experimentation and testing was needed.
"Only in this way can the true reasons for the CTV building collapse be known."
After the collapse, the Department of Building and Housing (DBH) launched a technical investigation into why the building collapsed.
A report released earlier this year identified three "critical factors" for the building's collapse, including concrete strength.
The royal commission has earlier heard from engineering experts who said the concrete in the building was "brittle like chalk."
But Dr Reay has rubbished the DBH report as being "technically inadequate", and today (Monday) attempted to shift responsibility for the concrete strength.
"Our company could not be held responsible... It was the contractor's sole responsibility," he said.
Low concrete strength results found in material from the CTV building was "negligible" anyway, said Dr Reay earlier.
Instead, he thought the building may have weakened after the September 4, 2010 magnitude 7.1 quake, and in particular, pointed to the effect of strain hardening on reinforcing steel.
The hearing, due to last eight weeks, continues tomorrow.