Many New Zealand homes built before 2008 were not required to have underfloor insulation. If your home is older or built on piles, there’s a good chance it’s losing warmth through the floor or has damp air rising from below. Both underfloor insulation and a ground moisture barrier can make a big difference to how warm and dry your home feels.
What Underfloor Insulation Does
Underfloor insulation helps stop heat loss from your floors. During winter, cold air and dampness from under the house can seep up through your floors. When this happens, your home feels colder and your heating has to work harder to keep the temperature comfortable.
Installing insulation under the floor creates a thermal barrier between the warm air inside and the cold air below. It traps heat where it belongs and keeps your home warmer for longer. You’ll notice fewer draughts through floorboards and a more stable temperature throughout the day.
What a Ground Moisture Barrier Does
A ground moisture barrier, also known as a vapour barrier or polythene sheet, is a thick plastic layer placed over the soil beneath your house. Its job is to stop moisture in the ground from rising into the air under your floor.
Without this barrier, dampness in the soil can evaporate and build up under your home. Over time, that moisture can cause a range of problems such as:
- A damp, musty smell inside
- Condensation on windows and walls
- Mould or mildew growth
- Damage to timber floors and framing
- Attracting insects or pests
A properly installed ground moisture barrier covers the entire area of exposed soil. The sheet is pinned to the ground and sealed around piles so no moisture can escape. Once in place, it prevents water vapour from rising and helps keep the subfloor space dry. It’s a simple, low-cost job that delivers long-lasting results.
Why Both Work Best Together
Underfloor insulation and ground moisture barriers each solve a different problem, but together they deliver the best results. Insulation keeps heat inside and cold air out. A ground moisture barrier stops dampness from entering the subfloor.
By combining both systems, you create a stronger barrier against cold and moisture. This helps reduce humidity, improves air quality, and makes your home more energy efficient. Homes that have both tend to feel drier and more comfortable, especially in areas with high rainfall or clay soil.
If you’ve ever noticed your home feeling chilly even when the heater’s on, or if there’s a musty smell after rain, it’s often due to moisture and heat loss from the floor area. Installing both underfloor insulation and a ground moisture barrier tackles both issues at once.
When to Check Under Your Home
If your house is built on piles or has a timber floor, it’s worth having a look underneath. You might find old or damaged insulation, or sometimes none at all. You can also check for signs of ground moisture, such as wet soil, water pooling, or mould on the subfloor framing.
Homes near the coast or in areas with poor drainage are more likely to have dampness under the floor. Over time, that moisture can make the air inside your home feel humid and unpleasant.
At Insultech, we often find that homeowners are unaware of how much difference a dry subfloor makes. Once insulation and a ground moisture barrier are in place, the home feels noticeably warmer and the air fresher.
Get Your Underfloor Sorted
If you don’t have underfloor insulation or a ground moisture barrier, or you’re not sure if you do, contact Insultech for a quote or to arrange a free assessment and find out what’s under your floor.
Wondering what your home needs?
We’ll check for free, anywhere in Hamilton and the Waikato.
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