The inquiry into the collapse of the CTV building in Christchurch has heard there is no evidence it was issued a design certificate.
The Canterbury Earthquakes Royal Commission of Inquiry is investigating why the CTV building failed in the 6.3-magnitude quake on 22 February 2011, killing 115 people.
David Harding, a civil engineer who was employed by architects Alan Reay Consulting to work as a structural engineer, helped prepare the detailed design of the building.
On Tuesday, in his second day of evidence, Mr Harding said he believed the builders who constructed it in 1986 worked from incomplete plans that did not include changes made at a later date.
Mr Harding said that due to these "mistakes of bureaucracy" the CTV building was never issued a design certificate.
Mr Harding conceded there were significant design weaknesses, when he was presented with several statements from other witnesses.
They included civil engineering expert Professor John Mander, who described the build as a very liberal interpretation of the code.
When asked whether he stood by his claim the building met the codes of the day, Mr Harding conceded there were, in fact, "significant weaknesses" in its design.
Mr Harding told the commission on Monday Alan Reay built his reputation on designing buildings no stronger and no more expensive than they had to be.
He said engineers got their hands slapped for adding extra elements to buildings.