Condensation on windows: how to stop it and prevent mould

2 min read · 8 steps · Updated 3 October 2026

Wet windows in the morning are the first sign that a home is too humid. Left alone, the water runs into the frames, and black mould follows on the seals and in the corners of the room. A household puts a surprising amount of water into the air, up to 100 litres a week according to the UK's Energy Saving Trust, through cooking, showering, drying clothes and breathing.

If you rent, report damp, mould or pests to your landlord in writing early. Some causes are faults in the building that you cannot fix yourself.

Step by step

1. Air the rooms in short bursts

   Open the windows wide, several times a day, for at least five minutes each time. Opposite windows open together work fastest. A window left tilted all day lets less moisture out and cools the walls, which makes condensation worse.

   Done

2. Use the extractor fans

   Run the bathroom fan during a shower and for at least 15 minutes after it. Use the cooker hood while cooking and for 15 minutes afterwards. If the bathroom has no fan, open the window and keep the door shut until the steam is gone.

   Done

3. Make less steam

   Put lids on pans. Close the kitchen and bathroom doors while cooking and showering, so the moisture does not spread to colder rooms.

   Done

4. Dry laundry sensibly

   Dry clothes outside whenever the weather allows. Indoors, use one room with the door closed and the window open, or a dehumidifier next to the airer. A vented tumble dryer must blow to the outside.

   Done

5. Wipe the water away

   In the morning, wipe the windows and frames with a cloth or a window vacuum and wring the cloth out in the sink. After showering, pull the water off tiles and glass with a squeegee.

   Done

6. Keep the home warm enough

   Cold rooms get damp. Keep all rooms at a steady moderate temperature in winter instead of letting some go cold, and do not heat a cold bedroom with warm, moist air from the rest of the home through an open door.

   Done

7. Let the air move

   Keep trickle vents in the window frames open and clear. Leave a gap between large furniture and outside walls, so air can pass behind and the wall does not stay cold and damp.

   Done

8. Consider a dehumidifier

   If airing is not enough, for example in a basement flat or with a lot of laundry, a dehumidifier takes litres of water out of the air each day. A cheap hygrometer shows whether it is needed: aim for roughly 40 to 60 percent humidity.

   Done

Good to know

Condensation between the two panes of a double-glazed window is different. The seal of the unit has failed and the glass unit needs replacing.

Not all damp is condensation. A tidemark low on a ground-floor wall points to rising damp. A patch that grows after rain points to water coming in from outside, through a gutter, roof or wall. Both need a builder, or the landlord.

If mould has already appeared: how to get rid of bathroom mould.

Airing in bursts loses less heat than tilted windows. More on heating costs: how to lower your energy bill and how to bleed a radiator.

In short: Air in short bursts several times a day, fans for 15 minutes after showering and cooking, lids on pans, laundry outside or with a dehumidifier, wipe windows dry, keep rooms evenly warm.