Condensation, Damp and Mould: Causes and Practical Fixes

Black mould in the corner of a bedroom, water on the inside of windows and a musty smell are all signs that moisture is not being managed in a home. They are common, especially in colder months, and in most cases they can be reduced with a few practical changes. It is important to work out which type of damp you have, because the fix differs.

Condensation

Condensation is the most common cause. Warm air holds more moisture than cold air. When that moist air meets a cold surface, such as a window, an outside wall or a corner behind furniture, the moisture turns to water droplets. Everyday activities add moisture to the air: cooking, showering, drying clothes indoors and even breathing.

Other types of damp

Penetrating damp: water getting in from outside, for example through a leaking roof, blocked gutter or damaged brickwork. It often shows as a damp patch that gets worse after rain.
Rising damp: moisture moving up from the ground through walls, usually showing as a tide mark low down on the wall. It is less common than people think, and often misdiagnosed.
Leaks: from pipes, appliances or overflows, which can be hidden.

If you are unsure, ask a qualified surveyor for an independent opinion before paying for expensive treatment.

Reducing condensation

Ventilate while moisture is produced. Use extractor fans or open a window when cooking and showering, and keep doors closed so that moisture does not spread to other rooms.
Dry washing carefully. Dry clothes outside when possible, or in a ventilated room with the door closed. Avoid drying clothes on radiators, which pours moisture into the air.
Keep the home warm enough. Cold rooms create cold surfaces. A steady, moderate temperature is better than short bursts of high heat.
Leave space around furniture and avoid pushing wardrobes tightly against cold external walls.
Use lids when cooking, and cover pans.
Consider a dehumidifier as a supplement if needed, but they use electricity, so they should not replace ventilation and fixing causes.

Cleaning mould

For small areas of surface mould, wipe it off with a damp cloth and a suitable mould cleaner or detergent, wearing gloves and ventilating the room. Do not dry-brush mould, as it can release spores. Redecorate with anti-mould paint only after you have fixed the underlying cause, otherwise it will come back.

Health

Damp and mould can irritate the airways and may make asthma and other breathing conditions worse, particularly for children, older people and people with existing health problems. If you have symptoms, speak to your GP.

Insulation and ventilation work together

Improving insulation raises the temperature of wall surfaces and reduces condensation, but you must keep adequate ventilation. See our guides on draught-proofing and keeping your home at a comfortable temperature.

If you rent

Tell your landlord or housing association in writing about damp and mould. Landlords have responsibilities for repairs and for keeping homes safe, and the rules differ across the UK. Contact your local council or an organisation such as Shelter or Citizens Advice if problems are not fixed.