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Condensation and mould

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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.

Last updated 31 October 2022