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Condensation, damp and mould

Spores of black mould on a wall made damp by condensation

Damp can cause mould on walls and furniture and cause wooden window frames to rot. It’s also unhealthy.

Last updated, June 2022

Why has my home got damp or mould?

Some damp is caused by condensation. This can lead to a growth in mould that appears as a cloud of little black dots. For other kinds of damp, see box below.

Condensation occurs when moist air comes into contact with a colder surface like a wall, window, mirror etc. The air can’t hold the moisture and tiny drops of water appear. It also occurs in places the air is still, like the corners of rooms, behind furniture or inside wardrobes.

How to reduce condensation in your home

Produce less moisture

Simple things make a huge difference, like keeping lids on pans when cooking, drying clothes outdoors (not on radiators), venting your tumble dryer to the outside and avoiding paraffin heaters or flue-less bottled gas heaters.

Let the damp air out and the fresh air in

Extractor fans are a good way to get rid of moist air and steam so that less condensation forms. Some very modern homes have extractor fans which run continuously, fitted in the ceilings of bathrooms, shower rooms and toilets. They use little electricity and don’t add much to your bill.

If your home doesn’t already have extractor fans then it is worth getting them fitted in the bathroom and kitchen. Fans that run on a timer, humidistat or pull-cord (e.g. when you turn on the bathroom light) typically have a rating of8-30W, so would cost about 10p if they were on all day.

Stop moist air getting into the rest of your home. When cooking or bathing, keep the kitchen or bathroom door shut and open the window to let the steam out.

Meanwhile, let fresh air circulate to avoid mould forming where the air is still. Make sure there is a gap between your furniture and the walls, and give wardrobes and cupboards a good airing sometimes.

Insulate and draught-proof your home

Warm homes suffer less from condensation, so you should make sure your house is well insulated. This means insulating your loft to the recommended depth of 270mm (about 11 inches), and your cavity walls (if your house has them). Your windows and external doors should be draught-proofed, and you should consider secondary glazing if your windows are draughty.

Heat your home a little more

While you don’t want to waste money heating rooms you don’t use, very cold rooms are more likely to get damp and mould. Set the thermostatic radiator valve to 1 in unused rooms so the radiator gives out a little bit of heat whenever you have the heating on. If you don’t have central heating, consider using a room heater with a timer and temperature control. Remember, unused rooms will need a good airing from time to time.

Top tips to reduce condensation, damp and mould

You can catch condensation dripping from windows with condensation channels and sponge strips (available from DIY shops). If you wipe down windows and sills in the morning this will also help, but be sure to wring out the cloth rather than dry it on a radiator. In extreme circumstances you may need to invest in a dehumidifier. These can help a lot but cost anything from £40 to over £200 and larger ones can be quite costly to run.

And finally, if you already have mould on your walls and ceilings then you need to clean it off properly. An effective method is to start by cleaning off the mould with spray containing bleach. This will help remove the staining that persistent mould can leave behind. Leave to dry overnight and then spray the affected area with an anti-fungal wash and allow that to dry. Always follow the manufacturer’s instructions and consider wearing a face mask when spraying.

You could also treat the affected area with a mould-resistant paint, available from most major hardware stores.

Condensation is not the only cause of damp

Your home may be experiencing damp for other reasons.

‘Penetrating damp’ is moisture entering the house through leaking pipes, a damaged roof, blocked gutters, gaps around window frames and cracked rendering and brickwork etc. All these problems can be remedied.

‘Rising damp’ is due to a defective or non-existent damp course. This will leave a ‘tide mark’ about 1m above the floor. Fixing rising damp is a job for a qualified builder.

Newly built homes can sometimes feel damp because the water used during construction (in cement, plaster etc) is still drying out.

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