Damp and mould in the home

Dampness can occur in homes for many different reasons. The problems it can cause include the growth of mould and mites, difficulties in keeping your home warm and damage to the building, for example collapsed ceilings and rotten window frames. This page describes the common causes of dampness and what should be done to deal with them.

Household damage causing dampness

There are many types of damage that can lead to water leaking into your home. These include:

  • Leaking pipes and overflows;
  • Rain water entering through holes in the roof;
  • Blocked or damaged guttering;
  • Rising damp caused by a defective or missing damp course;
  • Gaps in the external walls or around windows; and
  • In newly built houses, water used in construction still drying out.

These problems often leave a tide mark or coloured stains where the water is entering. The cause of the damp should be repaired as soon as possible. Unfortunately, it will likely take many weeks of heating and ventilation to dry the dampness out. Using a dehumidifier can help. If you see black mould growing, this is likely caused by condensation.

What is condensation?

There is always moisture in the air. When air gets colder, it holds less of this moisture and so tiny drops of water form. You will have seen this when you see your breath on a cold day, water forming on the side of a cold glass, or when the bathroom mirror mists over when you have a bath. Condensation usually occurs in cold weather on both wet and dry days. It happens on cold surfaces and in areas with little air movement. Signs of condensation include:

  • Water forming on windows;
  • Mould growth on window frames;
  • Damp and mould forming on external walls;
  • Mould forming in areas behind large pieces of furniture including wardrobes or cupboards;
  • Mouldy clothes;
  • Rotting leather goods, caused by high humidity;
  • Mould growth in corners of rooms and in the junction between ceiling and walls.

Interstitial condensation

This type of condensation happens when warm, moist air soaks into a wall, ceiling or floor before hitting a cold surface within. The air quickly cools and water is left as dampness on the surface. This can look like rising damp and the two are often confused. Interstitial condensation can lead to rot and corrosion.

How can I avoid condensation?

Condensation happens when the amount of heating, ventilation and moisture production in a home are not balanced. Prevent this by:

1. Producing less moisture – many things people normally no produce lots of moisture very quickly. Help reduce this by:

  • Covering saucepans and not leaving kettles boiling. This will also help to reduce energy bills;
  • Not using paraffin or portable flue-less bottled gas heaters – these put lots of moisture into the air as they burn fuel;
  • Drying washing outdoors
  • If you need to dry clothes indoors, do this in the bathroom with the door closed and the extract fan on or the window open;
  • Venting any tumble dryers to the outside, unless they condense to a water tank or directly to the drain;
  • Always opening the window to allow moist air to escape after a bath or shower.

2. Ventilate to reduce moisture – you can ventilate your home without making draughts:

  • Keep a small window ajar or a trickle vent open when using a room. Do not leave windows wide open for hours in winter as this will allow cold air in from the outside – leaving them open no more than 1 – 2 cm is enough for background ventilation. Use the lockable ventilation position on your window if this is available;
  • Ventilate kitchens and bathrooms when in use by opening windows wider. Ideally, fit humidistat controlled fans in these rooms that come on automatically when air becomes too moist;
  • Use a cooker hood that vents to the outside. Re-circulating hoods simply move moisture back into the kitchen;
  • Ventilate cupboards and wardrobes. Cut a ventilation slot in the back of each shelf or in the back of wardrobes (remember to ask for your landlord’s permission where necessary). Leave a gap between large pieces of furniture and walls. Where possible, place wardrobes and furniture against internal walls. Do not overfill them as this prevents good air circulation;
  • Ask for any new windows to be fitted with trickle vents;
  • Do not block permanent ventilation points as these are there to help to ventilate your home;
  • Do not completely block chimneys – fit an air brick with a louvered grill.

3. Keep your home warm – fitting insulation and draught excluders will help keep your home warm, reduce condensation and cut energy bills. Remember that insulation and heating installation works need to comply with building regulations, so check with the Council’s Building Control office before starting work (see BCR below). Useful steps include:

  • Insulate your loft and draught proof the loft hatch (BCR);
  • Install cavity wall insulation. Make sure the installer notifies the Building Control office;
  • Dry line large solid walls with thermal insulation (BCR);
  • Install secondary or double-glazed windows to reduce heat loss and draughts (BCR);
  • In cold weather, keep background heating on all day, even when there is no one at home. Remember to adjust the input and output controls on night storage heaters to make sure they produce an even temperature throughout the day;
  • Install fixed heating rather than using portable heaters. This should ideally be a gas central heating system or other economic means of heating such as a night storage heater. Heaters should have reliable thermostatic and time controls (BCR);
  • Do not draught proof a room where there is a cooker or a fuel burning heater. Ask a Gas Safe registered engineer for advice if you are not sure.

Dealing with existing condensation and mould growth

Once condensation happens, it will keep getting worse unless you take steps to control it. It cannot be cured overnight. Along with the above advice, you will need to:

  • Control mould growth – this can be done be wiping affected surfaces with a fungicidal wash that has a Health and Safety Executive ‘approval number’. Follow the manufacturers’ instructions carefully. Dry-clean mildewed clothes and shampoo carpets. Do not brush mould as this can release spores into the air;
  • Remove excess moisture from your home – wipe water off windows and surfaces as it forms, and then wring the cloth out over the sink. Alternatively, you can use a dehumidifier. You will need to be patient, as this process can take a lot of effort and time;
  • Keep the property warm and ventilated – you will not beat condensation unless your home is kept warm and you ventilate;
  • Once the moisture and mould are under control, you can consider painting the worst affected walls with a mould resistant paint. Do not overlay with normal emulsion paint or wallpaper.

Useful information

Useful information on effective ways to heat and insulate your home can be obtained from: