A warning to landlords: double check what new insulation rules will mean for you.

Last week it was revealed 20 kiwi kids are dying each year from the likes of asthma, pneumonia and bronchiolitis, because leaky and mouldy homes are making them sick.

From July 2019 all rental properties must have underfloor and ceiling insulation under the Residential Tenancy Act.

Energy Efficiency and Conservation Authority Programme Manager Robert Linterman said some landlords don't realise insulation will have to be at a certain level to comply with the Act.

"Landlords may think they are insulated stick their head into the ceiling and see ah yes we've got insulation and therefore we're compliant."

He said many landlords are leaving the job to the last minute which will make it more expensive later by creating a bottleneck in insulation supply.

"The problem that I see is the demand will outstrip supply and it's a bit like the housing market, the price will go up.

The Ministry of Business, Innovation and Employment has set separate standards of insulation for different parts of New Zealand.

EECA is offering half price insulation for low-income rental homes, until the middle of next year.

Linterman said we're half way through the application period, but only a quarter of those eligible have taken up the offer.

He said landlords need to apply now or risk missing out.