Ground Moisture Barrier
Bare ground under your home can release up to 40 litres of moisture a day. We lay a polythene barrier over it, so that moisture stays out of your floors, your insulation and your air.
Ground Moisture Barrier Installation: Stop Rising Damp at the Source
Rising Damp Starts Under Your Floor
Up to 40 litres of moisture can evaporate from the bare earth under an average NZ home every day. It rises into your floor timbers, carpet and walls. You notice it as a musty smell, mould in the wardrobe and a house that takes ages to warm up.
Our teams lay a heavy-duty polythene ground moisture barrier over that earth so the moisture stays in the ground. It's one of the quickest ways to dry a home out from underneath, and it protects your floors and any insulation you've put under them.
Signs Your Subfloor Has a Moisture Problem
- A musty smell that's strongest near the floor
- Condensation on the windows that comes back every morning
- Mould in wardrobes, corners or behind furniture
- Cold floors with cupped or soft boards
Any of these could point to damp coming up from the ground. An assessor can look under your house and tell you what's happening.
What Is a Ground Moisture Barrier?
A ground moisture barrier (also called a vapour barrier in NZ) is a heavy-duty polythene sheet laid across the bare earth under your home. It blocks moisture from evaporating into the subfloor and moving up into the floor above.
We overlap the seams by at least 100mm and tape them, then fix the sheet around the piles and the perimeter so it stays in place. That gives you one continuous layer across the whole subfloor.
How Our Ground Moisture Barrier Installation Works
1. We inspect the subfloor
We check access, drainage and the condition of what's under your house.
2. We lay the sheet
The polythene goes across the earth from wall to wall.
3. We overlap and tape the seams
Joins are lapped and sealed so moisture can't find a gap.
4. We fix the barrier and tidy up
The sheet is secured at the piles and perimeter, and we clear our gear away.
Most installations take 30 to 60 minutes. A larger subfloor or tight access can add time, and we'll give you an estimate when we quote.
Pair It With Underfloor Insulation
Damp insulation loses its performance, so we can install your barrier on the same visit as your underfloor insulation. You get a dry subfloor and insulation that does its job, with one team and one booking. Ask us at your assessment which Warmer Kiwi Homes funding applies to your job.
What a Dry Subfloor Does for Your Home
- Drier air inside – Less moisture rising means fewer damp patches and less mould.
- Warmer floors – A dry subfloor is easier to heat, and the same goes for the rooms above it.
- Protected timber – Dry joists and floorboards are less likely to rot or cup.
- Insulation that keeps working – Dry batts hold their shape and their performance.
Join us under the house at your free assessment. We'll show you what's down there, explain what it needs and give you a quote. No Worries.
Healthy Homes Moisture Barrier Compliance for Landlords
All private rentals must meet the Healthy Homes Standards, and landlords who don't comply risk penalties. The moisture ingress and drainage standard requires a ground moisture barrier wherever a rental's subfloor space is enclosed.
When you book a compliance visit with us:
- We install to standard – The barrier is lapped and fixed to NZS 4246.
- We check drainage – Barrier and drainage are checked in the same visit.
- You get the paperwork – We provide the documentation for your compliance records.
Our landlord page covers the other Healthy Homes requirements, including insulation and heating.
Frequently Asked Questions: Ground Moisture Barrier
If you rent out a home with an enclosed subfloor, the Healthy Homes Standards require one. Homeowners don't have to install one, but it makes sense if your subfloor has bare earth and you're noticing damp, mould or a musty smell. We check the subfloor at your assessment and tell you what it needs.
It depends on the size and access of your subfloor. We'll give you an estimate when we quote.
It stops moisture rising from the ground. It won't fix a leaking pipe or poor drainage, which is why we check drainage during the visit.
We have 12 branches from Whangarei to Otago. Find your local team on our branches page or ask us when you call.
We give a one-year workmanship warranty on installation, alongside any manufacturer warranties. The full terms are on our terms and conditions page.
Ready to Dry Out Your Subfloor?
Book your free assessment online or call us on 0800 888 766, 8:00am to 4:30pm, Monday to Friday.