Builders are being put on notice about the need for secure safety nets to stop workers seriously injuring themselves if they fall off roofs or walls.
WorkSafe has issued an industry-wide alert for residential building sites about the dangers of poorly installed and badly made nets.
Safety net failures in Auckland have caused two serious head injuries in the past two years, the health and safety regulator said.
The nets hang below high-level work areas, such as roofs on residential construction sites, and are designed to stop workers falling far and badly hurting themselves.
WorkSafe construction sector lead Vadim Spice said poor quality nets and untrained installers led to the accidents resulting in serious injury.
"In the Auckland region, we've had three reported incidents in two years ... Two serious head injuries as a result of falling, impacting into the net, the net failing and falling another two metres to the concrete floor below. So the worst case scenario actually."
'We've had three reported incidents in two years ... two serious head injuries" - WorkSafe's Vadim Spice
Although safety nets are not mandatory, employers are required to protect workers from serious harm.
Mr Spice said there were other ways of keeping builders safe, such as air-filled bags, polystyrene-filled bags and membranes that get rolled out like a canvas.
"There are a lot of products out there. Safety nets just seems to be the one that fits best with the residential builder."
Fall Arrest Safety Nets Association spokesperson Craig Daly said nets were becoming more widely accepted in the industry.
"There was some reticence initially, I think, when WorkSafe had the push on for fall protection. But I think now that most responsible builders are aware that they need to provide some means of protection for the workers on site, and that's a good thing."
The nets cost about $700 to install.
Mr Daly said they should put up only by properly registered installers.
Registered Master Builders Association president Simon Barber wouldn't go as far as saying nets should be compulsory, but said WorkSafe should do more to ensure more builders used them.
"At the moment everyone has their own interpretation of what complies," he said
For the first time WorkSafe issued its alert in both English and Chinese, as an estimated third of construction in Auckland involves Chinese builders.