"My life will never be the same."
Mr Harding said his 40-year engineering career would end in September.
IPENZ doesn't have jurisdiction to hand down any sanctions to Mr Harding, after he quit his membership earlier this month.
The hearing was today told that Mr Harding re-registered with his professional body just five months after the CTV disaster but didn't admit being behind its design 25 years earlier.
"It's a significant issue ... not a small detail. It was a calamitous event that occurred just five months before," said Peter McCombs, of the IPENZ investigation committee that looked into three complaints laid by Tim Elms, on behalf of 53 bereaved family members who lost loved ones in the disaster; the Department of Building and Housing; and IPENZ itself.
The omission, Mr McCombs said, breached IPENZ rules that states members must "act with honesty, objectivity and integrity".
Mr Harding denied being misleading, dishonest, or deceitful during his application.
The IPENZ investigation committee relied on the findings of the Royal Commission of Inquiry into the Canterbury Earthquakes, as well as an interview with Mr Harding -- who was not present today - last August.
The investigation team concluded that Mr Harding was inexperienced in multi-storey design and was wrong to think that anyone was going to oversee his work.
The committee agreed with the royal commission's findings that the building lacked ties between floors and walls, didn't have enough concrete reinforcing, and lacked "roughening" of construction joints between precast and in situ concrete.
The royal commission report criticised Dr Alan Reay of design firm Alan Reay Consultants for giving his inexperienced structural engineer Mr Harding "sole responsibility" for its design.
Dr Reay was also criticised for not reviewing his designer's final plans, but since he also resigned from IPENZ earlier this year, he has avoided the disciplinary process.
Dr Maan Alkaisi lost his wife Dr Maysoon Abbas, 61, in the magnitude-6.3 tremor.
Since then, he's discovered the building was illegally built and did not meet the building standards of the day.
Dr Alkaisi expressed disappointment that no serious action had been taken by either Government, police, or IPENZ against those responsible for the collapse.
He hoped that IPENZ would change its current system to prevent engineers from cancelling membership and avoiding accountability, and to prevent a future tragedy from happening.
Mr Elms, whose daughter Teresa died in the collapse, was disappointed by the resignations of Mr Harding and Dr Reay.
He closed the hearing with an emotional tribute to his daughter Teresa, who left behind two young sons, Henry, 2, and Thomas, eight months.
"Not a day goes by that I do not shed a tear. I miss her so much. I'll never get over this. I'd gladly exchange places with her if I could."
The disciplinary committee reserved its decisions.
