Holmes Consulting Group engineer John Hare examined the building for a potential buyer in 1990 and quickly found the connections between the building's key support wall and its floors did not meet building standards.
"The building would effectively separate from the shear walls well before the shear walls themselves reached their full design strength," he told the commission on Friday, quoting from his 22-year-old report.
He had told the building's designers, Alan Reay Consultants, about his concerns and drew up strengthening plans for the remedial work, which was estimated to cost $14,000.
But after the potential buyer, Canterbury Regional Council, pulled out of the sale, Holmes Consulting Group was told to stop its remedial work, Fairfax reports.
Dr Alan Reay gave evidence for the fifth time on Friday, telling the commission he became aware of issues with the building's structure in 1991, just five years after its construction was completed.
Drag bars were installed to strengthen the building, but Dr Reay maintained that to this day, he would not have called for a total building inspection, despite weaknesses that both he and Mr Hare had identified, Radio New Zealand reported.
The alterations were later found to not comply with the building code.
Meanwhile, the inquest into the 115 deaths in the building in its collapse during the February 22, 2011, quake will resume in October.
Coroner Gordon Matenga will conduct the inquest with a focus on six victims who survived the building's initial collapse but could not be rescued.
The hearing was adjourned in September last year, pending further investigations into the circumstances around the deaths.