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Avoiding condensation and mould

Dampness caused by excessive condensation can lead to mould growth on walls, ceilings and furniture, mildew on clothes and other fabrics and the rotting of wooden window frames. Damp and humid conditions provide an environment in which house dust mites can easily multiply. The presence of mould and dust mites can make existing respiratory conditions such as asthma and bronchitis worse. 

There is always some moisture in the air, even if you cannot see it. If air gets cold, it cannot hold all the moisture produced by everyday activities. Some of this moisture appears as tiny droplets of water, most noticeable on windows on a cold morning. 

This is condensation. It can often be seen in the bathroom on cold surfaces such as mirrors and wall tiles or cold walls after you have a bath or shower. It is not always visible especially on surfaces such as wallpaper.

Condensation occurs mainly during cold weather, whether it is raining or dry. 

Look for condensation in your home. It can appear on or near windows, in corners, behind curtains and in or behind wardrobes and cupboards. Condensation forms on cold surfaces and places where there is little movement of air.

Other causes

Condensation is not the only cause of damp. It can also come from:

  • Penetrating damp from roof, window and plumbing leaks. This kind of damp is usually focused in one place and will dry once the leak is fixed.
  • Rising damp due to defective damp-proof course or because there is no damp-proof course. Rising damp will only occur on the ground floor or basement level, generally no higher than a metre above ground level. This sort of damp is rare and almost never causes black mould.

These causes of damp often cause a ‘tidemark’ and you should have the necessary repairs carried out to remove the source of damp. If your home is damp for any of these reasons it may take weeks of heating and ventilating to dry out. If you do not think the damp comes from any of these causes, it is probably condensation. 

Treating condensation and mould

  • Dry windows and window sills every morning, as well as surfaces in your kitchen or bathroom that have become wet. After rinsing, wring out the cloth rather than drying it on a radiator
  • Treat bad outbreaks of mould, wipe down or spray walls with a fungicidal wash that carries a Health and Safety Executive (HSE) number. These are available at many DIY stores and supermarkets. Ensure that you follow the instructions for safe use
  • Dry-clean mildewed clothes and shampoo carpets
  • Don’t try to remove mould by using a brush or vacuum cleaner
  • You may need to strip wallpaper and treat the surface underneath. After treatment, re-decorate using good quality mould resistant paint and mould resistant wallpaper paste

Avoiding condensation

Minimise moisture

Everyday activities add extra moisture to the air inside our homes. Even breathing adds some moisture - one person asleep adds half a pint of water to the air overnight and a full pint when active during the day. 

  • Hang your washing outside to dry if possible. If you need to hang it inside, hang it in the bathroom with the door closed and a window open or extractor fan on. Don’t be tempted to put it on radiators or in front of portable heaters
  • If you use a tumble dryer, make sure it is vented to the outside of the property or that it has a condenser.
  • Always cook with pan lids on and turn the heat down once the water has boiled. Only use the minimum amount of water necessary for boiling.
  • When filling your bath, run the cold water first then add the hot. This will reduce the steam by 90% which will help to prevent condensation.
  • Try to avoid the use of bottled gas heaters as they produce about 8 pints of moisture from an average sized gas cylinder.
  • Don’t use your gas cooker to heat your kitchen as it produces moisture when burning gas (you might notice your windows misting up).

Improve air movement

Ventilation can help to reduce condensation by removing moist air from your home and replacing it with drier air from outside.

  • ‘Cross-ventilate’ your home by opening the first notch of a small window upstairs and a small window downstairs (they should be on opposite sides of the house, diagonally opposite if you live in a flat). At the same time, open all interior doors. This will allow drier air to circulate throughout your home. Cross-ventilation should be carried out for about 30 minutes each day.
  • Open ‘trickle’ vents on your windows, if you have them.
  • Ventilate your kitchen when cooking or washing by hand. A window slightly open is as good as one wide open.
  • Keep kitchen and bathroom doors closed to prevent moisture escaping into the rest of your house
  • Ventilate your kitchen and bathroom for about 20 minutes after use by opening a small window. Use an extractor fan if possible, they are cheap to run and very effective, but remember to close the door.
  • Ventilate your bedroom by leaving a window slightly open at night.
  • Keep a small gap between large pieces of furniture and the walls and, where possible, place wardrobes and furniture against internal walls. Pull shelves away from the backs of wardrobes and cupboards. Never overfill wardrobes and cupboards as it reduces air circulation.

Insulate and draught proof

Condensation forms more easily on cold surfaces in the home, for example walls and ceilings. In many cases those surfaces can be made warmer by improving the insulation and draught proofing. Insulation and draught proofing will also help to keep the whole house warmer and will cut your fuel bills. When the whole house is warmer, condensation becomes less likely.

Loft and cavity wall insulation are the most effective forms of insulation. There are also insulation products (rolls and sheets) available that can be applied to the inside surface of walls that can’t be cavity insulated, typically in older properties. Sloping ceilings in older properties can also be insulated in this way. 

Draught-proofing is one of the cheapest and most effective ways to save energy and money. Controlled ventilation helps to reduce condensation and damp by letting fresh air in when needed. However as draughts are uncontrolled they let in too much cold air and waste too much heat. To draught proof your home you should block up unwanted gaps and let cold air in and warm air out.

If you are a tenant and have reason to believe that your home could benefit from an improvement to its loft or wall insulation, please contact your landlord to enquire about the possibility of such an improvement. 

Heat your home

The warmer air is, the more moisture it will hold. Heating one room to a high level and leaving other rooms cold makes condensation worse in the unheated rooms. If you don’t want to heat your entire home, keep the doors shut on unheated rooms.

The World Health Organisation guidelines suggest 21 degrees in a living room and 18 degrees in the bedrooms, falling lower at night and when you are out. You don’t need to keep your home at these temperatures all the time, but you should aim to bring it up to these temperatures at least some of the day. 

A short burst of high level heating only warms up the room’s air temperature. Low or medium level heating over a longer period will heat the air temperature and the fabric of the house, such as the walls. Once heated, the fabric will retain some of the added warmth, which in turn will reduce the time and amount of heat needed in warming the room up the next time. 

Heating controls such as thermostats and timers can be used to ensure you have adequate levels of heating in the right places at the right times, this can also help reduce heating bills.

Keeping the heating on low all day in cold weather will help to control condensation, but keep a check on your meters to check how much it is costing you.

Last updated 14 December 2021