Your New Home's Windows Are Crying. Here's What They're Trying To Tell You.
Most people think it's a window problem. It's usually a humidity problem. And the solution is almost always ventilation.
You wake up on a cold Adelaide morning and every window in your home is covered in water.
The first thought is usually: “The windows must be leaking.”
The second thought is: “I should have spent more money on better glazing.”
In most cases, neither is true. Your windows aren't leaking. And better glazing might not fix it either.
The key insight: windows don't create condensation. They reveal it. Your windows are simply the first cold surface in the room — the first place your home's moisture problem becomes visible. The moisture itself, and the conditions driving it, are usually found elsewhere.
Why does condensation form on windows at all?
Think of a cold beer on a warm day. The glass doesn't leak — water from the surrounding air condenses onto the cold surface. Windows work the same way.
Every combination of air temperature and humidity has a dew point — the temperature at which water vapour becomes liquid. When a surface drops below that dew point, condensation forms. The equation is simple:
Surface temperature < Dew point temperature → Condensation forms
Windows are usually the coldest visible surface in a room, which is why they are where moisture first becomes visible. But the condensation isn't coming from the windows — it's coming from the air.
“My old house never did this”
This is one of the most common things homeowners in new builds say — and it deserves a direct answer.
Older homes didn't have less condensation because they were better buildings. They had less visible condensation because they leaked air everywhere — around windows, under doors, through wall cavities and roof spaces. Moisture generated by occupants simply drifted out through the gaps. The ventilation was accidental.
Modern homes are deliberately built more airtight. This is a good thing — it's why they use less energy and feel more comfortable. But airtight construction without designed ventilation means the moisture stays inside until it finds a cold surface.
A family of four can easily generate 10–15 litres of water vapour every day through cooking, showering, drying clothes and simply breathing. In a draughty 1960s home, much of that escaped. In a modern NCC 2022 home, it doesn't — unless there's a ventilation system designed to remove it.
Older home
Leaky construction allowed moisture to escape through gaps. Low visible condensation — but also high heat loss, draughts, and poor comfort.
Modern airtight home
Deliberate airtightness keeps heat in and draughts out. But without designed ventilation, moisture accumulates. Windows become the messenger.
How much moisture does your family actually create?
Most people have no idea how much water vapour daily life generates. It's one of the most powerful concepts in building science — and one of the least explained.
| Activity | Moisture Generated |
|---|---|
| Sleeping (2 adults) | ~0.5–1 litre per night |
| Showering | ~0.5 litre per shower |
| Cooking dinner | ~1–3 litres |
| Drying clothes indoors | 2–5 litres per load |
| Family of 4 — total | 10–15 litres per day |
That's the equivalent of tipping a bucket of water into your home's air every single day. In a draughty old home, most of it drifted out. In a modern airtight home without ventilation, it has nowhere to go.
Why aluminium windows condensate first
Aluminium is an excellent conductor of heat. Cold outdoor temperatures transfer rapidly through a standard aluminium frame to the internal face. In practical terms, the frame becomes one of the coldest surfaces in the room — often colder than the glass itself.
This is thermal bridging: a continuous conductive path between the cold outside and the warm inside. It's why condensation on standard aluminium windows often starts at the frame, not the glass — and why people assume the window is faulty when it isn't.
How better windows help — and where they can't
Thermally broken aluminium and uPVC frames raise the internal surface temperature, which raises the threshold at which condensation forms. This genuinely helps — but with an important caveat.
| Window Type | Condensation Risk | Internal Frame Temperature |
|---|---|---|
| Single Glazed | Very High | Very Cold |
| Double Glazed Aluminium | High | Cold |
| Thermally Broken Aluminium | Medium | Warmer |
| Double Glazed uPVC | Low | Warm |
| Passive House Certified | Very Low | Warmest |
Internal frame temperature — outside 4°C, inside 21°C
Illustrative values. Higher = warmer internal surface = less condensation risk.
The important caveat: a family generating 15 litres of moisture per day can still cause condensation on excellent windows if indoor humidity isn't controlled. Better windows raise the threshold. They don't eliminate the root cause. If your relative humidity regularly exceeds 65%, even Passive House certified windows may show condensation on very cold mornings.
The actual problem: indoor humidity
This is where the real solution lives. Reduce indoor humidity and you raise the dew point threshold — meaning surfaces need to be colder before condensation forms. The effect is often larger than upgrading glazing.
| Indoor Relative Humidity | Condensation Risk |
|---|---|
| 30–40% | Very Low |
| 40–50% | Low |
| 50–60% | Moderate |
| 60–70% | High |
| 70%+ | Very High |
The healthy target for indoor relative humidity is 40–55%. Below this, condensation risk drops sharply and mould cannot establish. Above 60%, condensation becomes likely on standard aluminium windows in Adelaide winters. Above 70%, even thermally broken frames will struggle.
Why condensation is usually worse in bedrooms
Many homeowners notice that bedroom windows are far wetter than living room windows — even when both face the same direction. This isn't a coincidence.
Bedrooms are closed for 7–9 hours overnight. Two adults sleeping in a room generate roughly half a litre of water vapour between them — with nowhere for it to go. The door is shut, the heating drops, and the windows are the coldest surfaces in the room. By morning, the conditions are almost ideal for condensation.
Closed door: Moisture generated overnight is trapped in the room rather than diluted across the house.
Two people breathing: Each person exhales roughly 200ml of water vapour per hour during sleep.
No fresh air exchange: Without ventilation, CO₂ and humidity both rise throughout the night.
Lower overnight temperatures: Heating drops overnight, lowering window surface temperatures and making condensation more likely.
This is where MVHR makes the most immediate difference. A system that continuously supplies fresh air to bedrooms and extracts stale, humid air overnight keeps both CO₂ and humidity in check — without opening windows in a cold Adelaide winter.
It's also worth noting that poor overnight air quality — elevated CO₂ and humidity — is directly linked to disrupted sleep. If condensation in the bedroom is a sign of high humidity, the same air quality issues are likely affecting sleep quality too. See: Poor Sleep & CO₂.
Why are my windows wet? Use the calculator
This tool shows not just whether condensation will form, but what's driving it. Try the default settings — a typical Adelaide winter morning — then drag the humidity slider down to 45% and watch what happens.
Why Are My Windows Wet? Calculator
Adjust the inputs to see whether condensation will form — and more importantly, why.
Condensation likely
Dew Point
14.2°C
Frame Temp
10.8°C
Glass Temp
13.9°C
Humidity
65%
Try: 21°C inside / 4°C outside / 65% humidity — a typical Adelaide winter morning.
A tale of two Adelaide winters
Without MVHR
🌡 Outside: 4°C
🏠 Inside: 21°C
💧 Humidity: 65%
🪟 Standard aluminium windows
❌ Condensation likely on frame and glass
Same home with MVHR
🌡 Outside: 4°C
🏠 Inside: 21°C
💧 Humidity: 45%
🪟 Same standard aluminium windows
✅ Condensation unlikely
The same windows. The same outdoor temperature. The same home. The only difference is that MVHR continuously removes moisture from the indoor air, keeping humidity in the safe zone. No window upgrade required.
Window condensation is the visible warning
Window condensation is easy to notice because you can see it. But the same high-humidity conditions affect every cold surface in the home — many of them hidden.
If your windows are consistently wet, it's worth checking those other surfaces too. The conditions that cause window condensation are the same conditions that grow mould — and mould in the back of a wardrobe is much harder to notice than water on a window.
Mould in New Homes
Why new homes develop mould and what actually fixes it
Damp Bathrooms
The bathroom condensation and moisture problem explained
Poor Sleep & CO₂
How indoor air quality affects sleep and health
What Is MVHR?
How mechanical ventilation with heat recovery works and why it matters
Blower Door Testing
How airtightness is measured — and why it matters for moisture control
Is condensation on windows ever normal?
Not everything needs immediate investigation. Here's a practical guide to what's generally within normal range and what's worth looking into.
Generally normal
Worth investigating
Frequently asked questions
Why are my new home windows wet every morning?
Morning condensation on windows is almost always caused by high indoor humidity combined with cold window surfaces. Overnight, windows cool down — if your indoor humidity is elevated, moisture condenses on the glass. New homes are especially prone to this because they are more airtight than older homes, trapping moisture generated by cooking, showering, breathing and drying clothes.
My old house never had condensation. Why does my new home?
Older homes leaked air everywhere — around windows, under doors, through wall cavities and roof spaces. That moisture escaped by accident. Modern homes are deliberately built more airtight, which is excellent for energy efficiency and comfort. But without controlled ventilation to replace the ventilation that used to happen through gaps and cracks, moisture builds up indoors. This is why new homes often have more condensation than older homes, not less.
Will better windows fix my condensation problem?
Better windows raise the surface temperature and reduce condensation, but they only address one side of the equation. If indoor humidity is high enough, even Passive House certified windows can show condensation. The most effective approach combines thermally broken or uPVC frames with ventilation that keeps indoor relative humidity in the 40–55% range. In many cases, improving ventilation has more impact than upgrading glazing.
Can condensation on windows lead to mould?
Yes. Window condensation is a visible sign that indoor humidity is high enough for moisture to form on surfaces. The same conditions that cause window condensation also cause moisture to form on cold corners, in wardrobes against external walls, behind furniture and in bathroom ceilings. Left unaddressed, this creates ideal conditions for mould growth throughout the home — not just at windows.
Windows don't create condensation. They reveal it.
If water is forming on the inside of your windows, your home is telling you something about its temperature, humidity and ventilation. Better windows can help. Better ventilation often helps more. Understanding the difference can save thousands of dollars and create a healthier, more comfortable home.
If you're considering spending thousands on new windows to solve condensation, it's worth understanding whether the problem is your glazing, your humidity levels, or your ventilation strategy first.
Condensation isn't always a window problem. It's often a ventilation problem.
If you're experiencing condensation, mould, stale air or high indoor humidity, HiPer Haus can assess your home's ventilation strategy and recommend practical solutions that improve comfort, indoor air quality and building durability.