You sealed the house. Now it’s damp.
Wet windows every winter morning is the most common complaint we hear from people who have just done everything right. It is not a fault in the work. It is the predictable next problem, and this is how to fix it.
The short answer
A draughty house dries itself out through its own gaps. Seal those gaps and you keep the warmth in, and you keep in the water from showers, cooking, washing and breathing too. That water settles on the coldest surface it can find, which is your windows first and the inside of your walls later. The fix is moving air on purpose: fans that really vent outside, used properly, and in a well sealed home a proper ventilation system. There is no rebate for any of it anywhere in Australia, and anybody who tells you otherwise is quoting the wrong scheme.
The quick test
Wet windows most winter mornings means the air in your house is holding more water than it can carry overnight. It is a ventilation problem, not a window problem.
Do this first
Check your bathroom fan actually vents outside and not into the roof. This one thing is wrong in a surprising number of houses.
Be careful of
Anybody promising a permanent fix or quoting you a ventilation rebate. Neither exists.
Why sealing causes it
The water was always there. The gaps used to take it away.
A household puts a surprising amount of water into its own air every day. Showers, cooking, the kettle, drying clothes inside, the dishwasher, and simply breathing. In a leaky old house that damp air drifts out through the gaps, along with all your heat. It is why cold draughty houses feel dry as well as cold.
Seal the gaps and both stop leaving. The warmth stays, which is what you paid for. The water stays too, which nobody mentioned. Warm air holds a lot of water, but only while it is warm. Overnight the house cools, the air can hold less, and the water comes out onto the coldest surface in the room.
That is your window glass first, because glass is cold. It is why the wet appears there rather than anywhere else. Leave it a few winters and it happens inside walls too, and in wardrobes on outside walls. There it is much harder to see and much dearer to fix.
This is not a reason to skip sealing
Sealing is still the cheapest and best value work in the house. It just has a second half. Do the sealing and the ventilation in the same season and the problem never starts.
What actually fixes it
Four fixes, cheapest first.
Make your existing fans work
Check the bathroom fan vents to the outside rather than into the roof space. Run it during the shower and for twenty minutes after, not just while you are in there. Same in the kitchen. Both of these cost nothing and they are wrong or unused in a lot of houses.
Why it comes here
Free. Removes the moisture at the moment it is made, which is far easier than dealing with it later.
Who does it
Nobody, unless the fan turns out to vent into the roof. Then an electrician or a ventilation installer.
Change a few habits
Dry washing outside or in a vented dryer rather than on a rack in the lounge. Put lids on pots. Open two windows on opposite sides for ten minutes in the morning, even in winter. It costs you very little heat and it dumps a lot of water.
Why it comes here
Free, immediate, and it is often the whole answer in a house that is only mildly damp.
Who does it
You.
Subfloor ventilation
If your house is on stumps and the ground under it is damp, moisture comes up through the floor all year. Vents and sometimes fans move air through that space instead. This is the fix for musty smells and for damp that is worst at floor level.
Why it comes here
Solves a source of moisture rather than managing the result. Only relevant on a raised floor.
Who does it
A subfloor ventilation specialist. Ask them to explain where the water is coming from before they quote.
A ventilation system
A heat recovery system moves stale wet air out and fresh air in, all day. It passes the warmth from the outgoing air to the incoming air, so you keep the heating you paid for. This is the proper answer for a genuinely tight house, and it is the most expensive.
Why it comes here
The right fix once a house is well sealed. Not needed in a leaky one, which is another reason order matters.
Who does it
A ventilation installer. Ask for the airflow rate they are designing to and why.
There is no rebate
Not one, anywhere in the country.
We went looking properly, because a figure for ventilation subsidies circulates widely and a lot of people arrive expecting one. There is no ventilation, heat recovery, subfloor or mould rebate in any Australian state or territory scheme. Not one.
The number people have usually seen is a reverse cycle air conditioner discount, reattached to the wrong job somewhere along the way. If a quote mentions a ventilation rebate, ask which scheme and ask for the government page. There is not one to show you.
That is worth saying plainly, because it changes how you should read a quote. This work comes out of your own pocket, so treat it like any other purchase. Get more than one quote. Ask where the water is really coming from. And be careful with anybody promising a permanent fix. Nobody can promise that, because how a house is lived in is half of the problem.
When it is not your bill
Two different problems that look the same.
There is a difference between damp that has built up slowly and damage from a sudden event. A burst pipe, a storm or a split washing machine hose is usually an insurance matter. The insurer directs the work, and the job is a repair rather than an upgrade.
Condensation, rising damp, a wet subfloor and poor ventilation are the other kind. They happen slowly and they are almost never covered. They are also the ones people put off year after year, because no deadline forces the issue.
Work out which one you have before you start ringing people, because they lead to completely different conversations. If there was a sudden event, call the insurer first.
What we couldn’t confirm
Three things in circulation that are not true.
This is the topic with the most wrong information attached to it of anything on this site. These are the specific claims we checked and could not stand up.
A $500 to $1,600 ventilation subsidy
We checked the state scheme activity lists. There is no ventilation activity in any of them. The figure appears to be a reverse cycle air conditioner discount attached to the wrong job.
Aged care funding for damp and mould work
The home support programs fund things like grab rails and ramps through contracted providers. A consumer cannot pick a business off a directory and have it paid for.
“Multi zone humidity control heat pumps”
This is a ducted or multi head reverse cycle air conditioner under a different name. It is a real product with a made up category around it.
Quick answers
The questions people ask next.
Is a dehumidifier enough?
In one room, for a while, yes. It treats the symptom and it costs power to run every day. If the whole house is doing it, you are better off spending that money on moving air instead of drying it.
Should I just open a window?
Genuinely, it helps a lot. Ten minutes with two windows open on opposite sides, morning and evening, dumps a large amount of moisture for very little heat. It is the cheapest thing on this page.
Is mould dangerous?
It can affect people with asthma and allergies, and a large or recurring growth is worth taking seriously. If somebody in the house is unwell, that is a question for a doctor rather than for an installer.
Can I clean it myself?
A small patch on a hard surface, yes. Anything large, anything that keeps coming back in the same spot, or anything inside a wall is different. The water is still arriving, and cleaning is not the fix.
Will double glazing fix condensation?
It moves it. Warmer glass means the water condenses somewhere else instead, often somewhere you cannot see. It helps, but it is not a ventilation fix.
How do I know if the house is too tight?
A cheap humidity meter is the honest answer. If your indoor humidity sits high through winter and the windows are wet most mornings, that is the signal, whatever the house looks like.
What to do this week
Three things, and two are free.
Tonight
Go outside and check where your bathroom fan comes out. If you cannot find a vent on the wall or the roof, it is blowing into your ceiling.
This week
Buy a cheap humidity meter and leave it in the room with the wet windows. A week of readings is worth more than a guess.
Before quoting
Work out whether the water is coming from inside the house or up from under it. They are different jobs and different trades.
When you’re ready for help
Find the right help for your next step.
Get a whole-home plan
A home energy assessor can look at your whole home, identify the biggest opportunities and help you work out what to tackle first to make it more comfortable, efficient and cheaper to run.
Find an assessor near youFind the right specialist
Once you know which upgrade you need, find a business that specialises in that type of work and services your area.
Find a specialist near youKeep reading
