Do I Need a Ground Moisture Barrier?

November 12, 2021

As we head into spring and drier weather, it’s a good time for Property Managers and Landlords, to include maintenance checks that aren’t carried out with your regular inspections, starting with under the rental property.

If a rental property has a suspended floor and 50% or more of the sub-floor perimeter is obstructed, then a ground moisture barrier is required to meet the Healthy Homes Standards. If you know the rental already has a barrier installed, then it needs to be checked for any rips or tears as these allow moisture to flow and pool above the barrier and will need to be repaired or covered.

On average, 1.5 cups of water can evaporate from each 1m² of ground in 24 hours – that’s over 250 cups a day for a 150m² house! This moisture causes rot, mould, mildew, affecting health and causing expensive structural damage if not fixed.

So it’s important to reduce moisture levels by installing a ground moisture barrier so get in touch today and have a chat to our friendly team.

Common Questions Ground Moisture Barrier

What is a ground moisture barrier?

A ground moisture barrier (also called on-ground vapour barrier) is a polythene groundsheet that is placed over the ground, under houses, to prevent rising dampness. Ground moisture barriers installed after 1 July 2019 must either meet the specifications in NZS 4246:2016 or achieve a vapour flow resistance of at least 50 MNs/g and be installed by an appropriate professional installer.

How do you install a ground moisture barrier?

You can download the New Zealand Standard, Energy efficiency – Installing bulk thermal insulation in residential buildings (NZS 4246:2016) here.

Or get in touch with us for a copy

Do ground moisture barriers work?

Dollar for dollar, installing a ground moisture barrier is one of the best things you can do to improve the health and comfort of your home. BRANZ research has found ground moisture barriers to be the most effective option at addressing subfloor moisture and more effective than subfloor vents.

Are there subsidies for ground moisture barriers?

Warmer Kiwi Homes grants are available to homeowners (not for rental properties) if you are also eligible for the insulation grant, so check the EECA website to see if you qualify.

How much does a moisture barrier cost?

Installation of a 250mu Polythene Moisture Barriers that complies with new Healthy Home Standards, will cost $7.99 per m2 however G-Force Healthy Homes Solutions is running a Spring into Spring promotion so now $6.80 per m2

Is a ground moisture barrier required for the Healthy Homes Standards?

If your rental property has a suspended floor and 50% or more of the sub-floor perimeter is obstructed then a ground moisture barrier is required.

Do I need a ground moisture barrier?

Many Kiwi homes suffer from damp and mould and subfloor moisture is potentially the largest source of moisture in the home depending on the occupants habits. BRANZ research shows us that this could be up to 40 litres each day under a 100 square metre house, even if the soil appears dry. If the subfloor ventilation is inadequate then much of this moisture will pass through the flooring and into the atmosphere inside the house. Often the subfloor ventilation will not be enough to fully get rid of this moisture.

Additionally, installing a ground moisture barrier for homes with an accessible sub-floor cavity is a requirement of the Moisture Ingress and Drainage Standard – Healthy Homes Standards 2019.

Can I install a Ground Moisture Barrier myself?

Yes, it is possible to install a Ground Moisture Barrier yourself. However, it is not the nicest of jobs getting under the underfloor.

Our trained installers are experts and can install a Ground Moisture Barrier quickly and efficiently plus we guarantee our work for 5 years.


At G-Force Healthy Home Solutions we’re all about making homes warmer, drier and more energy efficient for Kiwi families.

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