Healthy Homes – Ground Moisture Barrier


From the 1 July 2021 a landlord must ensure that their rental property complies within 90 days of a new tenancy but all rental properties must be compliant by 1 July 2024.

We have talked about most of the other requirements in the Healthy Homes Act but haven’t discussed the ground moisture barrier requirements. It is estimated that around 1.2 million New Zealand homes have suspended timber floors and a lot of those are in Auckland. We encourage rental property owners to start making the necessary upgrades to their rental property now as it is very likely that 90 days will not be sufficient time for landlords to comply with all of the requirements come 2021.

Why Moisture Barrier?

On average, 250ml of water can evaporate from 1m² of ground in 24 hours. Moisture under a house can cause mould and mildew inside the house, affecting the health of the occupants. Even apparently dry ground will produce about 25 kg of water vapour per day – going straight up into the house (BRANZ data).

Installing heavy duty builders polythene (no less than 0.25mm thick) as a groundsheet effectively reduces rising damp and can lower the moisture level in the home.

The product is available from most hardware stores and is around $8 per sqm, for those DIY landlords, however for the vapour barrier to be effective it needs to be correctly installed. Leaks from water or waste pipes, wet areas, cladding and so on must be dealt with before the material is laid.


The vapour barrier should completely cover the soil and sheets should overlap a minimum of 75 mm and should be butted up to surrounding foundation walls and piles. Sheets should also be weighted down to avoid being moved by the ventilating air movement.


Find out about funding options for making a warmer drier home here.

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