Hundreds of closures ordered as checks reveal home builders are disregarding rules.
More than half of home building sites inspected in a safety clampdown have been closed or ordered to stop dangerous practices.
And so many builders are not meeting guidelines to prevent falls from residential building sites that watchdogs are extending by two months the operation to check them.
The enforcement operation is worrying builders, who say the guidelines will force up costs for homeowners.
But those behind the crackdown say it is vital to counter high rates of injury and death on worksites.
The government campaign started in July. Since then, more than 400 actions have been taken against 760 construction sites for not complying with guidelines on safe working at height.
Inspectors shut down 215 of the sites, and issued more than 160 written warnings requiring immediate remedial action.
The ACC estimates the lifetime cost of an accident resulting in paraplegia can be as high as $10 million.
More than 50 per cent of falls are from less than 3m, and 70 per cent are from ladders and roofs. The cost of these falls is estimated to be $24 million a year.
Francois Barton, head of a Ministry of Business, Innovation and Employment programme to reduce workplace harm, said the huge personal and financial toll was one of the reasons for the campaign.
"New Zealand health and safety performance by international standards is poor. We are significantly behind Australia and you are almost twice as likely to be killed or seriously injured in a New Zealand workplace compared to a British workplace."
Workplace injuries and fatalities cost New Zealand about $3.5 billion annually and 100 people on average die each year.
The construction industry's death and injury rate was significantly high, Mr Barton said. "And falls are one of the leading contributors to construction's toll."
Jeff de Leeuw, the Hamilton director of house-building company G.J. Gardner, said the guidelines were costly, confusing and time-consuming.
His company was investing thousands of dollars in equipment to comply with the guidelines to keep workers safe but "it is challenging when there is a lack of consistency in the solutions offered".
Mr de Leeuw said meeting the requirements would cost each house-buyer an extra $4000, which on the 14,547 building consents issued between August last year and July would total $58 million.
Voice of experience - Rhett Brown
Rhett Brown's complaints about safe building practices fell on deaf ears weeks before a 2.2m fall from a single-storey deck broke his neck.
Mr Brown was 52 and semi-retired after 20 years in the police when he was paralysed from the fall in 2004.
His life was changed forever. He lost his wife, house, income and independence, and spent six months in the Auckland Spinal Unit at Otara and 2 years in a rest home needing round-the-clock care.
Now 61 and an educational speaker on workplace health and safety, he says the "falls from height" campaign is worthy. But he's worried about bad habits entrenched on building sites.
"I just couldn't believe the widespread stupidity and the way it was accepted. I don't think you can do strict enforcement without massive education."
He said construction workers should understand the risks of their job.
"And look after your mates. If they complain to you something isn't safe, don't walk away from them, support them."
Guidelines include using:
•Safe working platforms, guardrail systems, edge protection, scaffolding, elevated work platforms, mobile scaffolds and barriers to restrict access.
•Work positioning systems or travel restraint systems, safety harnesses, industrial rope access systems and soft landing systems.