Damp can cause mould on walls and furniture, and make timber window frames rot. The growth of mould and mites can increase the risk of respiratory illness. Some damp is caused by condensation, we will explain how condensation forms and how you can keep it to a minimum, so reducing the risk of dampness and mould growth.
What causes damp?
There is always some moisture in the air, even if you cannot see it. If the air gets colder, it cannot hold all the moisture and tiny drops of water appear - this is condensation. You notice it when you see your breath on a cold day, or when the mirror mists over when you have a bath. Condensation occurs mainly during cold weather, whether it is raining or dry, it does not leave a ‘tidemark’ and is normally accompanied by the development of mould. It appears on cold surfaces and in places where there is little movement of air. Look for it on external walls, in corners, on or near windows, in or behind wardrobes and cupboards. It often forms on north-facing walls.
Leaks, penetrating or rising damp
Condensation is not the only cause of damp. It can also come from:
- Leaking pipes, wastes or overflows
- Penetrating damp from rain seeping through the roof (where a tile or slate is missing); spilling from a blocked gutter; penetrating around window frames or through damaged brickwork.
- Rising damp due to a defective/breached damp-course or because there is no damp-course. These causes of damp often leave a ‘tidemark’. If your home is newly built it may be damp because of water used during its construction (for example, in plaster) and is still drying out. It can take weeks of heating and ventilation to dry out a new home. A dehumidifier will help.
Why is there mould and how to tackle it
Mould will grow on most surfaces where there is moisture. It will colonise walls, ceilings, windows, fabrics, clothing and furniture. Mould does not usually grow on walls which are affected by rising or penetrating damp. When damp moves
across a wall it causes salts from within to come to the surface and these salts stop the mould from growing.
The only way of permanently getting rid of mould is to deal with the underlying condensation problems.
Treat the existing mould
To kill and remove mould, wipe down walls and window frames affected with a fungicidal wash, which carries a Health and Safety Executive ‘approval number’. Follow the manufacturer’s instructions carefully. Dry-clean mildewed clothes and shampoo carpets. Distributing mould by brushing or vacuum cleaning can increase the risk of respiratory problems.
After treatment, redecorate using a good quality fungicidal paint to help prevent mould recurring. Note that this paint is not effective if overlaid with ordinary paints or wallpaper.
Produce less moisture
Some ordinary daily activities produce a lot of moisture very quickly. Did you know that the average household produces over 20 pints of moisture in one day?
- Cover cooking pans in use and do not leave kettles boiling
- Avoid using paraffin and portable flueless bottled gas heaters as these heaters put a lot of moisture into the air.
- Dry washing outdoors on a line. If this is not possible put it in a single room (ideally the bathroom) with
the door closed and the window open and/or extractor fan on.
- Vent any tumble dryer to the outside, unless it is the self-condensing type. DIY kits are available for this.
- When running a bath, or filling a bowl of washing up water, run the cold water first and then add the hot water second as this produces less steam than running hot first or at the same time.
Ventilate your home
You can ventilate your home without making draughts:
- Keep a small window ajar when someone is in and keep trickle ventilators open all the time.
- Ventilate kitchens and bathrooms when in use by opening windows wider. Or better still, use a humidistat controlled extractor fan. These come on automatically when the air becomes humid, and are cheap to run.
- Close the kitchen and bathroom door when these rooms are in use, even if your kitchen or bathroom has an extractor fan. Closing the door will help prevent moisture reaching other rooms (especially bedrooms which are often colder and more likely to get condensation).
- Ventilate cupboards and wardrobes. Avoid overfilling them as this stops the air circulating. Cut a ventilation slot
in the back of each shelf or use slatted shelves. Cut ‘breather’ holes in doors and in the back of wardrobes and leave
space between the back of the wardrobe and the wall. Where possible, position wardrobes and furniture against internal walls. If you replace your window units at any time, make sure that the new frames incorporate trickle
- Wipe off wet surfaces, for example where condensation has formed on windows, or after using the shower. This
means that the ventilation will be more effective in removing the remaining moisture. Wring out any cloth used rather than drying on a radiator.
Insulate, draught-proof and heat your home
Insulation and draught-proofing can keep your home warm and cut fuel bills. When the whole home is warmer, condensation is less likely.
- Insulate your loft. Remember to draught-proof the loft hatch but do not block the opening under the
- Consider cavity wall insulation. Ensure any works are carried out by a qualified and registered installer
- Consider secondary and double glazing of windows to reduce heat loss and draughts (but you must ensure that there is some ventilation)
- In cold weather, keep low heating on all day, even when there is no-one at home (recommended temperature of 17°C)
- The heating ideally should be on for around 3 hours at a time and set to come on early morning when the air is coldest. If you are at home all day switch it on for 3 hour periods or leave it on full time but at a lower temperature.
What not to do
- Do not block permanent ventilators.
- Do not completely block chimneys. Instead, leave a hole about two bricks in size and fit a louvered grille over it.
- Do not draught-proof rooms where there is condensation or mould.
- Do not draught-proof rooms where there is a cooker or a fuel burning heater (e.g. gas fire).
- Do not draught-proof windows in the bathroom and kitchen.
- Do not wait until it starts to turn cold before putting your heating on. Leaving the heating off until the weather turns cold will result in the walls losing all their stored heat. It will take a lot longer (and cost more) for the heating to warm
them up sufficiently for you to feel comfortable.
- Do not put your heating on for one hour or less as this can make the problem worse. The air absorbs water vapour more quickly than the walls can warm up. When the heating is turned off the air cools rapidly
and condensation quickly occurs, cooling the walls further.