She was in hospital for two days after suffering a broken shoulder and bruising to her face, neck back and abdomen.
Titirangi Scaffolding was convicted, fined $20,000 and ordered to pay the victim $7000 in reparation.
The Ministry of Business, Innovation and Employment said the failure to secure the planks in accordance with scaffolding guidelines and New Zealand standards was not picked up in four inspections by a director of the company
"That's a woeful lack of attention to a major hazard which has caused a serious injury,'' said Keith Stewart, chief inspector investigations for MBIE's health and safety group.
"The homeowner had a right to expect that this equipment would be fit for use, but the company's failures have resulted in her suffering needless serious injury.''