Condensation & mould

How to prevent condensation, mould and damp in your home

Everybody generates moisture in their homes through normal daily activities such as cooking and bathing. Condensation of moisture and water vapour occurs on colder surfaces, and mould spores form on the surface when the vapour condenses into water.

Residents are responsible for ensuring that they create the right combination of heating, ventilation and treatment to keep their homes free from the effects of condensation.

Understanding condensation

What is condensation?
Is condensation causing the mould and damp?
What can I do about it?

There is always some moisture in the air, even if you can’t see it. If the air gets colder it can’t hold all the moisture and tiny drops of water appear. This is condensation. You may notice it when you see your breath on a cold day, or when the mirror mists over after you have a bath.

Condensation occurs mainly during cold weather, usually from October to April, whether it is raining or dry. It does not leave a 'tidemark' and appears in places where there is little movement of air. Look for black mould in corners of rooms, on or near windows, in or behind wardrobes and cupboards. It will often form on north-facing walls that don’t get direct heat from the sun.

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

  • Leaking pipes, wastes or overflows
  • Rain seeping through the roof where a tile or slate is missing, spilling from a blocked gutter, penetrating around window frames, or leaking through a cracked pipe
  • Rising damp due to a defective damp-course or because there is no damp-course.
  • Defective brickwork
  • The water used during construction, if you’re home is newly built and still drying out.

These causes of penetrating damp often leave a 'tidemark'. If you believe it to be one of the above causes, you should contact us and have the necessary repairs carried out to remove the source of damp.

It may take several weeks of ventilation to dry your home out, but using a dehumidifier will help.

If you do not think the damp comes from any of the above causes, it is probably condensation.

Firstly, treat the mould already in your home. To treat and remove the mould, wipe down the walls, ceiling, windows and door frames with a fungicidal wash in accordance with the manufacturer’s instructions. Do not use bleach as this is water based and does not actually remove the mould.

Do not try to remove the mould by brushing or vacuum cleaning as this can increase the risk of respiratory problems. Occupants of buildings with damp or mould are at increased risk of experiencing health problems such as respiratory symptoms, respiratory infections, allergic rhinitis and asthma.

The only way of avoiding severe mould is by eliminating the dampness, so if you deal with the basic problems of condensation, the mould should not reappear.

How to reduce condensation


  • Keep internal kitchen and bathroom doors shut, particularly when cooking, washing or bathing – otherwise water vapour will spread right through the house and condensation will probably reach external walls and ceilings in the other cooler rooms, particularly bedrooms.

Ventilation and windows

  • The more moisture produced in your home, the greater the chances of condensation and mould – unless there is adequate ventilation. Nobody likes draughts, but some ventilation is essential.
  • In winter, open the windows a little when they mist up.
  • If you fit draught stripping, leave a space for a small amount of air to get through.
  • If you have an extractor fan, use it when cooking or having a bath/shower to stop the windows getting steamed up

Kettles and pans

  • Don't allow kettles and pans to boil away any longer than is necessary, and always put the lid on the saucepan.

Heating and insulation

  • You will get less condensation if you keep your home warm most of the time. It is preferable to keep a steady low level of heating throughout the day rather than heating your home from cold each time.
  • Use the thermostats and/or thermostatic radiator valves (if fitted) to control your heating – this should also help to reduce your heating bills.

Drying clothes

  • Drying clothes indoors, particularly on radiators, will increase condensation unless you open a window to allow air to circulate.
  • If you have no other choice but to dry your washing at home then it would be better to do so by placing the washing on a clothes airer located in the kitchen or bathroom, shut the door, turn on the radiator and run the extractor fan (if there is one provided) or open the window a little.
  • If you have a tumble dryer which is not vented to the outside you must install a vent directly to the outside. This should be done by a qualified technician. 

Beds, cupboards and wardrobes

  • Don't overfill cupboards and wardrobes. Always make sure that some air can circulate freely by fitting ventilators in doors and leaving a space at the back of the shelves.
  • Keep beds, mattresses, blankets, quilts and pillows away from external walls so that the air can circulate freely.


  • Never block chimneys as it could be dangerous. If you are covering up a fireplace you must at least fit an air vent to allow ventilation. 


  • Always remember to put a small amount of cold water in the bath before you turn on the hot tap.


  • Do not run your shower for longer than needed.


  • Always remember to mop up any condensation or water as it forms or daily.


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