Mark Tresham was fined $4500 and ordered to pay $130 court costs, Auckland Council said.
He was prosecuted after a council investigation into the collapse found the deck was not compliant with the Building Code and had no building consent.
It collapsed during an 80th birthday party in Te Atatu, in September 2014, sending 13 people, including eight children, plunging to the ground. All escaped serious injury in the 3m fall, but five people received hospital treatment.
The council investigation found the deck was fixed to the house with nails only, rather than being bolted adequately as required by the Building Code.
Ian McCormick, general manager of Auckland Council Building Control, said he was satisfied with the result.
"The purpose of the regulations is to protect life and make sure buildings are safe for occupants," he said.
"All building works need to comply with the building code. Any kind of building work needs to have safety as the highest priority, and when the work requires building consent working with council ensures compliance, and therefore safety."
If people were unsure what was required they should contact the council before starting a project, he added.
At the time of the incident, Ola Maha, 40, said he and around 20 family members had just finished saying grace at his aunt's birthday party when the deck of his parents' two-storey home gave way around 4.20pm on September 14. Most of the adults were in the living room, and reported hearing a "big bang", and looked over to see the kids were gone.
"We said our family prayer in the living room, and after doing the birthday song and blowing out the candles, then family [members] started to walk to get the food [on the deck]. All of a sudden, bang."
By NZME. News Service
