Rental properties must be fitted with smoke alarms and insulated under laws that have just been passed by Parliament.
Smoke alarms must be fitted by July 1 this year and insulation must be in by July 1, 2019.
Building and Housing Minister Nick Smith says the legislation covers 120,000 properties that don't have smoke alarms and 180,000 that aren't insulated.
The Residential Tenancies Amendment Bill was passed into law unanimously tonight.
It also strengthens the enforcement of existing regulations around heating, dampness, electrical safety, plumbing, sanitation and ventilation.
Dr Smith says the smoke alarms are expected to save three or four lives a year, and making homes warmer and drier will save many more.
"These measures, according to my officials, are going to save, when fully implemented, 129 lives per year," he said.
"So over the next 10 years this bill is expected to save the lives of 1000 fellow New Zealanders and it's a measure that, on behalf of this Government, I am incredibly proud."
Opposition parties say the measures are insufficient, and Labour wants a warrant of fitness regime for all rental properties.
"It's another grudging half-measure from the Government," said Labour's housing spokesman Phil Twyford.
"It's something, but it's not enough."