Wet windows every morning, a musty smell in the wardrobe, black spots creeping across a bathroom ceiling: condensation and mould are a familiar part of winter in many UK homes. They're not just unsightly. Government guidance for housing providers says damp and mould can affect health, particularly for people with respiratory conditions, weakened immune systems, children and older people. This article explains why it happens and what you can do about it.
Why winter makes it worse
Warm air holds more moisture than cold air. Everyday life puts a lot of water into the air indoors: breathing, cooking, showers, boiling kettles and especially drying clothes inside. When that warm, moist air touches a cold surface, such as a window, an outside wall or the back of a wardrobe pushed against an outside wall, it cools and the moisture turns back into water. That's condensation.
In winter we keep windows shut, outside walls are colder, and we dry more washing indoors, so condensation builds up. Surfaces that stay damp for long periods give mould spores the conditions they need to grow.
Is it condensation or something else?
Not all damp is condensation. Other causes need different fixes:
- Rising damp usually shows as a tide mark low down on ground-floor walls.
- Penetrating damp comes from outside, such as a leaking gutter, damaged roof or cracked render, and often appears as a patch that gets worse after rain.
- Leaks from pipes, baths or the flat above.
Condensation tends to appear on windows, in corners, behind furniture and in bathrooms and kitchens, and gets worse in cold weather rather than after rain. If you think the cause is a leak or structural, it needs a repair, not just better habits.
Daily habits that reduce moisture
- Put lids on pans and use the extractor fan when cooking. Keep it running for a while afterwards.
- Shut the bathroom door during and after a shower, run the extractor fan or open the window a little, and wipe down the shower screen and tiles.
- Dry clothes outside when you can. If not, dry them in one room with the door closed and a window slightly open, or use a dehumidifier in that room. Avoid drying on radiators where possible.
- Wipe windows each morning with a cloth or a window vacuum, and wring it out down the sink rather than leaving it to dry in the room.
- Leave trickle vents open on modern windows. They're there to let a small, steady amount of air through.
- Air rooms briefly each day, even in winter: ten minutes with a window open lets moist air out without losing much heat from the walls and furniture.
- Move furniture slightly away from outside walls so air can circulate behind it.
Keep rooms evenly warm
Cold rooms and cold surfaces attract condensation. Keeping the home at a steady low heat often works better than letting rooms get very cold and then blasting the heating. The NHS suggests heating the rooms you use to at least 18°C if you can. Unheated spare rooms with the door shut are a common mould spot; open the door occasionally or keep a little heat in them.
Balancing this with the cost of heating is a real challenge. Our article on cutting heating costs in a UK flat suggests ways to stay warm without sealing up the ventilation.
When a dehumidifier helps
A dehumidifier pulls moisture out of the air into a water tank. It's most useful if you dry washing indoors, have a flat with poor ventilation, or have a persistent problem room.
- Compressor dehumidifiers work well in warmer rooms and are generally efficient at normal room temperatures.
- Desiccant dehumidifiers tend to perform better in cold spaces such as unheated rooms, garages or conservatories, but often use more power.
- Small "mini" dehumidifiers with a tank of under a litre a day help in a wardrobe or small bathroom, but won't keep up with a whole flat full of drying washing.
Check the extraction rate (litres per day at stated conditions), the tank size, noise level and whether it has a laundry mode and auto shut-off when full. A cheap hygrometer, which shows indoor humidity, helps you see whether your changes are working.
Cleaning small patches of mould safely
Small areas of surface mould on hard surfaces can often be cleaned:
- Ventilate the room and wear rubber gloves; a mask is sensible.
- Use a mould remover designed for the purpose, following the instructions, or a cloth with soapy water for very light marks.
- Don't brush or vacuum dry mould, as it spreads spores.
- Dry the area thoroughly afterwards.
Large areas, mould that keeps returning quickly, or mould on soft furnishings may point to a bigger damp problem. Anyone with asthma or other breathing problems shouldn't do the cleaning.
If you rent: what to ask your landlord
Landlords in England have obligations to keep homes free of serious hazards, and the government has published guidance on damp and mould for rented housing providers. It makes clear that damp and mould should not be blamed on tenants' "lifestyle" without investigating the cause.
- Report it in writing, with dated photos, and keep a copy.
- Ask for faults to be fixed: broken extractor fans, leaking gutters, failed seals, missing trickle vents or a heating system that doesn't work properly.
- If nothing happens, contact your local council's environmental health or private housing team, or get free advice from Citizens Advice or Shelter.
Rules differ in Scotland, Wales and Northern Ireland, so check the guidance for where you live.
A quick checklist
- Wipe windows each morning and air rooms briefly every day.
- Use extractor fans, lids and closed doors when cooking and showering.
- Dry washing outside, or in one ventilated room, or with a dehumidifier.
- Keep rooms evenly, gently warm rather than very cold then very hot.
- Report leaks, broken fans and persistent mould to your landlord in writing.
For warm, low-cost kit that helps you heat less without sealing up the home, see our warmth without the bill guide.