The healthy home library
What causes mould in UK homes?
Mould needs moisture. The government's guidance describes four kinds of damp: condensation, penetrating damp, rising damp and leaks. Here's how to tell them apart.
A little clarity.
A healthier home.
Condensation
The most common kind of damp: moisture from everyday life settling on cold surfaces.
Cooking, bathing, washing and drying clothes all put water into the air. When warm, moist air meets a cold wall, window or ceiling, the water condenses and mould can grow. It is usually worst in winter.
Where to look
What helps
- Use extractor fans when cooking and bathing, and leave them on for a while afterwards
- Keep internal doors shut when cooking or bathing, and use pan lids
- Keep windows on the vent setting or trickle vents open
- Dry laundry outdoors when you can
Penetrating damp
Water getting into the building from outside through a defect.
Leaking gutters and downpipes, damaged roofs, failed pointing or render, and poor window seals can all let rain in. Patches often get worse after wet weather.
Where to look
What helps
- Keep gutters and downpipes clear and in good repair
- Repair damaged roofs, pointing and render
- Check window and door seals
- Get a builder or roofer to find where the water gets in
Rising damp
Moisture from the ground rising up through walls or floors.
It is less common than condensation or penetrating damp. It usually shows as a tide mark low on ground-floor walls. Paths or flower beds built up above the damp-proof course can cause it.
Where to look
What helps
- Keep outside ground levels below the damp-proof course
- Keep air bricks clear
- Rule out leaks and condensation before paying for a new damp-proof course
- Consider an independent survey
Leaks and escapes of water
Water from pipes, radiators, baths, showers, sinks or appliances.
Slow leaks can go unnoticed for a long time, especially behind kitchen units, under baths or inside walls, and floods or burst pipes can soak a large area at once.
Where to look
What helps
- Fix drips and leaks promptly
- Check and replace worn sealant around baths and showers
- Know where your stopcock is
- Dry out thoroughly after any flood or burst pipe
How common is damp?
Serious condensation (3% of homes) was more common than penetrating damp (2%) or rising damp (1%). Source: English Housing Survey 2024 to 2025.
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