Why Tasmanian Homes Get Cold, Damp and Mouldy — and the Building Science That Fixes It

Ask around Tasmania and you’ll hear the same complaints about older and even brand-new homes: rooms that never quite warm up, windows streaming with condensation on a winter morning, and black mould creeping into corners, wardrobes and window reveals. Most people treat these as facts of life in a cool-temperate climate. They’re not. They’re symptoms of how the home was built — and they can be designed out entirely.

Here’s the building science behind the problem, and what a home has to do to solve it.

Why your home is cold

A home doesn’t stay warm because of how big the heater is. It stays warm because of how slowly it loses heat. Every Tasmanian winter, a leaky, under-insulated home loses warmth almost as fast as you can produce it — through gaps in the building envelope, through poorly insulated walls and ceilings, and through single or low-performance glazing.

That’s why so many homes feel cold even with the heating running: you’re constantly topping up heat that’s leaking straight back out. Turn the heater off and the temperature drops within the hour, because there’s nothing holding it in.

Why the damp and mould appear

This is where it gets important for your health, not just your comfort. Condensation forms whenever warm, moist air touches a surface colder than its dew point. In winter, the coldest surfaces in a typical home are the single-glazed windows and the poorly insulated wall junctions — and that’s exactly where you see the water beading and the mould taking hold.

Mould needs three things: moisture, a surface, and still air. A cold, leaky, poorly ventilated home gives it all three. Everyday living — showering, cooking, drying clothes, even breathing — puts litres of water vapour into the air, and if there’s nowhere for it to go and cold surfaces for it to land on, it condenses and feeds mould.

So the damp and the cold aren’t two separate problems. They’re the same problem: a building envelope that lets heat out and lets moisture accumulate.

The three things that fix it — for good

You can’t reliably fix this with a dehumidifier and a bigger heater. It’s fixed in how the home is built. Three things, working together as one system:

1. A continuous, well-insulated, airtight envelope. Continuous insulation with no gaps or thermal bridges keeps interior surfaces warm — and a warm surface can’t grow mould, because condensation never forms on it. Airtightness stops the uncontrolled draughts that carry heat out and moisture in. This is the single biggest lever, and it’s why we obsess over it on every energy-efficient home we build.

2. Performance glazing. Windows are usually the coldest surface in the house. High-performance double or triple glazing keeps the inside face of the glass warm enough that condensation stops forming. Certified Passivhaus windows transmit roughly one-sixth the heat of a standard Australian window — the difference between a window that sweats every winter morning and one that doesn’t.

3. Controlled ventilation. A well-sealed home needs deliberate ventilation, not accidental draughts. Mechanical ventilation with heat recovery (MVHR) supplies a constant stream of filtered fresh air and extracts stale, humid air — recovering most of the heat on the way out. You get fresh, dry air without opening a window to a cold, wet day, and the moisture that feeds mould never gets the chance to build up.

What “good” actually looks like

When these work together, the change is dramatic. A home built to the certified Passivhaus standard uses roughly 80–90% less heating energy than a typical build, holds a stable temperature across the whole home, and simply doesn’t get the condensation and mould that plague conventional houses. Our certified Passivhaus at Blackmans Bay was independently verified at a heating demand of just 10 kWh/m²·yr — and homes like it stay warm, dry and clean without a fight.

You don’t have to go all the way to full certification to feel the benefit. The same principles — a proper envelope, better glazing, controlled ventilation — improve the health and comfort of every home we build. That’s the whole idea behind a healthy home.

The honest part

Here’s what most people don’t want to hear: this is far easier and cheaper to get right when you build it in from the start than to bolt on afterwards. Retrofitting airtightness and continuous insulation into an existing home is possible but expensive and disruptive. If you’re building or renovating, the time to solve cold and damp forever is on the drawing board — before a single wall goes up.

If cold rooms, foggy windows and mould are the reason you’re thinking about building, you’re asking exactly the right question. Understand what “certified Passivhaus” actually means, or put your own power bills through our Passivhaus savings calculator to see what a genuinely warm, dry home would change.