The first cold days arrive and it's always the same story: you open the blind in the morning and the glass is soaking wet. Condensation on windows isn't a fault in the frames, it's water vapour the air in your home can no longer hold, settling on the coldest surface in the room. It can be fixed, but wiping it with a cloth isn't enough: you need to understand where that vapour comes from and get rid of it before it ends up in the walls.
Why condensation forms on windows
Warm air holds more moisture than cold air. A lived-in home produces several litres of vapour a day: showers, pans on the hob, laundry drying indoors, the breathing of whoever sleeps there. As long as the air stays warm, that vapour is invisible. The moment it touches the glass — the coldest point in the room in winter — it drops below dew point and turns back into liquid.
That's why condensation is most obvious in the bedroom when you wake up, in the bathroom after a shower and in the kitchen while water is boiling. And it's why single glazing is far worse: double glazing stays warmer and barely gets wet.
How to clear condensation from windows every morning
- Dry it straight away, don't wait. A rubber squeegee pulled from top to bottom takes off the bulk in half a minute; the water collects on the sill and you pick it up with a microfibre cloth.
- Check the frame and the sealant, not just the glass. That's where water sits, and exactly where black mould starts.
- Ventilate for 5 to 10 minutes with cross ventilation: two opposite windows wide open. It works far better than leaving one ajar for half an hour, and it cools the walls less.
- Wipe the seals with white vinegar diluted half and half with water, once a week. It kills the spores before they take hold.
- Pull the curtains back during the day. A curtain pressed against the glass creates a pocket of cold, damp air where condensation never evaporates.
Cutting damp in the home: the habits that really change things
Drying the glass treats the symptom. This is what actually brings relative humidity down:
- Put lids on your pans while cooking and switch the extractor on from the start, not once the kitchen is already full of steam.
- Dry laundry outside whenever you can. One load drying indoors releases two to three litres of water into the air. If there's no alternative, do it in a room with the window open and the door shut.
- Ventilate the bathroom after a shower, with the door closed, until the mirror clears.
- Don't switch the heating off completely in rooms you barely use. A cold room is the first to condense. A steady 19-20 °C beats turning it on and off.
- Leave a few centimetres between furniture and external walls so air can circulate behind them.
- Buy a hygrometer. It costs very little and settles any doubt: the aim is to stay between 40% and 60% relative humidity.
When condensation turns into mould
If water sits in the frame for several days, little black dots appear on the sealant first, then patches in the top corner of the wall. At that stage you can still sort it yourself: clean with water and diluted bleach or a dedicated mould remover, wearing gloves with the window open, and don't paint over it until the area is completely dry.
Two signs tell you the problem is no longer about ventilation: patches that come back in the same spot within a few weeks, and walls that feel cold to the touch even when the house is warm. That points to a thermal bridge or a leak, and at that point you call a professional instead of carrying on scrubbing.
Mistakes that make condensation worse
Leaving a window ajar all day doesn't ventilate, it just chills the wall and makes it condense even more. Drying clothes on the radiator sends all that water straight into the air. And closing the blinds fully every night cuts the glass off from the room's warmth: lower them, but leave the slats open.
With a two-minute routine in the morning and a short burst of proper ventilation, most homes get through winter without a single patch. If you're getting the house ready for the cold, take a look at our home selection.