How to Reduce Condensation and Damp in a Home

Condensation is one of the most common causes of damp and mould in New Zealand homes — and it isn’t only a winter problem. It forms whenever warm, moist indoor air meets a cold surface like a window or an outside wall, so it can show up any time the air inside holds more moisture than the home can clear. The fastest ways to reduce it are to put less moisture into the air, let stale air out and fresh air in, and keep the home warm and steadily ventilated — which is exactly what heat-recovery ventilation does automatically.

Damp homes are common here. Drawing on Stats NZ Census 2023 data, Environmental Health Intelligence NZ (EHINZ) reports that around 20.6% of New Zealanders live in a home that is sometimes or always damp, and about 16.5% live with visible mould the size of an A4 sheet or larger. It’s most obvious in the colder months — wet windows in the morning, a musty smell, black spots in the corners of cold rooms — but the underlying moisture is there year-round.

It’s a particular concern in compact, well-sealed modern homes — including portable and expandable homes — where warm, moist air has fewer gaps to escape through. That’s the trade-off with a warm, tightly sealed home: it holds heat well, but it also holds moisture unless it’s ventilated properly. It’s exactly why heat-recovery ventilation is fitted as standard in the homes we deliver, so the home manages that moisture from day one.

What causes condensation and damp indoors

Everyday living adds a surprising amount of water to the air: cooking, showers, drying washing inside, unflued gas heaters, and simply breathing. In a well-sealed home that moisture has nowhere to go, so it settles on the coldest surfaces. Three things drive the problem:

• Too much moisture going into the air — indoor drying, long showers, pots without lids.
• Not enough ventilation — windows stay shut to keep the warmth in, so damp air is trapped.
• Cold surfaces — single-glazed windows and poorly insulated walls give the moisture somewhere to condense.

Practical ways to reduce condensation

• Vent the moisture at the source — extractor fan or open window when cooking and showering; lids on pots.
• Dry washing outside or in a vented space — a load of washing dried indoors releases several litres of water into the air.
• Let fresh air in daily — even ten minutes of cross-ventilation clears a lot of built-up moisture.
• Keep the home gently warm — a warmer home holds more moisture as vapour instead of dropping it onto cold surfaces.
• Improve the cold surfaces — double glazing and good wall insulation reduce the spots where condensation lands.
• Add continuous ventilation — a heat-recovery ventilation unit brings fresh air in and pushes stale, damp air out around the clock, without throwing your warmth away.

How heat-recovery ventilation helps

Opening windows works, but it lets your warmth escape with the damp air — most of all in the colder months. Heat-recovery ventilation solves that trade-off: it draws fresh air in from outside through a filter, and as the stale air leaves, a ceramic core transfers most of its heat to the incoming fresh air. You get a steady supply of fresh, filtered air that helps reduce condensation, moisture and damp, while keeping the warmth you’ve paid for.

In our homes this comes standard. Heat-recovery ventilation is fitted as standard on our 20ft, 30ft and 40ft homes, the Horizon, the 40ft Glass Front and every Apple Cabin — the only model it isn’t fitted on is The Cabin. It draws fresh air in through an F7 filter that catches dust and pollen, has a CO₂ sensor that boosts fresh air when a room gets stuffy, runs quietly (under 28.7 dB) on just a few watts, and can be controlled from an app. It helps reduce condensation, moisture and damp — it doesn’t eliminate them, and how a home performs also depends on how it’s used, heated and sited.

Frequently asked questions

Why do my windows get wet on cold mornings?
Overnight, moisture from breathing, cooking and washing builds up in the air, and the coldest surface in the room — usually the window — is where it condenses. Reducing indoor moisture and adding steady ventilation are the two things that make the biggest difference.

Does ventilation make the house colder?
Opening windows does. Heat-recovery ventilation doesn’t in the same way — it recovers most of the heat from the outgoing air and transfers it to the fresh air coming in, so you keep ventilating without losing your warmth.

Do your homes come with ventilation?
Yes — heat-recovery ventilation is fitted as standard on our 20ft, 30ft and 40ft homes, the Horizon, the 40ft Glass Front and every Apple Cabin. The only model it isn’t fitted on is The Cabin.

Will it stop mould completely?
No home feature can promise that — mould also depends on heating, moisture habits and the site. Good ventilation, warmth and reduced indoor moisture together are what keep condensation and damp down.

Talk to us about a warmer, drier home

Our portable and expandable homes are supplied finished and delivered NZ-wide, with heat-recovery ventilation fitted as standard on every model except The Cabin, and transit insurance included the whole way to site. Prices are clear and incl. GST — from $38,500 for the 20ft, $51,000 for the 30ft and $64,000 for the 40ft.

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