Damp and mould guide
Is your home damp? Damp can cause mould on walls and furniture and make timber window frames rot. Damp housing encourages the growth of mould and mites which can increase the risk of respiratory illness.
Some damp is caused by condensation. This guide explains how condensation forms and how it can be minimised. Following this advice will help reduce the risk of dampness and mould growth.
Condensation may be caused by the way that the home is occupied, by a lack of heating and ventilation provision, or frequently by a combination of these. This guide gives advice to owner-occupiers, landlords and tenants about dealing with the problems of damp and mould.
If you are a tenant, you may need to ask for your landlord’s permission if you are thinking of carrying out any work.
What is condensation?
There is always some moisture in the air, even if you cannot see it. As the air gets colder, it cannot hold all this 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’. It appears on cold surfaces and in places where there is little movement of air. Look for it in the corners, on or near windows, in or behind wardrobes and cupboards. It often forms on north-facing walls.
Why is there mould?
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. These salts stop the mould from growing.
Mould does grow on areas affected by condensation. The only way of permanently getting rid of it is to deal with the underlying condensation problems so that the affected areas stay dry all the time.
Is it condensation?
Condensation is not the only cause of damp. It can also come from:
- Leaking pipes, wastes or overflows
- Rain leaking into the building, for example through a hole in the roof, blocked guttering or down pipes or penetration around window frames
- Rising damp due to a defective (or absent) damp-course
These causes of damp often leave a ‘tidemark’.
If your home is newly built it may be damp because the water used during its construction (for example, in plaster) is still drying out.
If your home is damp for any of these reasons it may take weeks of heating and ventilation to dry out, even after any problems have been cured. Using a dehumidifier will help.
These problems may lead to excessive moisture in the home and difficulties in keeping it warm. Buildings with these issues are more susceptible to condensation and mould. Any underlying damp problems need to be identified, and remedied, as part of the package of measures needed to deal with any condensation.
How to avoid condensation
The following steps will help you to reduce the condensation in your home:
Produce less moisture
Producing less moisture will reduce the amount of water which can condense onto affected areas.
Some ordinary daily activities produce a lot of moisture very quickly: You can reduce this by:
- Covering saucepans and not leaving kettles boiling
- Avoiding the use of paraffin and portable flueless bottled gas heaters (which put a lot of moisture into the air in the rooms)
- Drying washing outdoors on a line or putting it in the bathroom with the door closed and the window open or fan on
Ventilate and remove moisture
Removing moisture will reduce the amount of water which can condense onto affected areas.
There is always a difficulty with balancing warmth, ventilation and (in some cases) security. To remove moisture from your home without making draughts:
- Ensure that tumble dryers are properly vented (see manufacturer’s instructions for the appliance). Alternatively, use a condensing or heat pump tumble dryer
- Keep a small window ajar or a trickle ventilator open when someone is in the room
- Ventilate kitchens and bathrooms when in use. After use open the windows wider to remove the remaining moisture
- Where you have an extract fan, it may be helpful to have this linked to the lighting circuit and provided with a 20 minute “over run” so that the fan continues to work after you have finished in the room.
- Extractor fans are cheap to run and typically use less electricity than an energy saving light bulb.
- Fitting an extract fan, particularly a humidistat-controlled electric fan, may be helpful in some situations. Humidistat controlled fans operate automatically when the air becomes humid. Choose one which can also be switched on manually
- Close the kitchen and bathroom doors when these rooms are in use, even if your kitchen or bathroom has an extractor fan. This will help prevent moisture reaching other rooms, especially bedrooms, which are often colder and more liable to condensation problems
- Ventilate cupboards and wardrobes. Avoid putting too many things in them as this stops the air from circulating. Where possible, position wardrobes and furniture against internal walls. Leave a space between the back of the wardrobe and the wall
- If you replace your window units at any time, make sure that the new frames incorporate trickle ventilators
- Dehumidifiers may help to remove moisture; however, these only work efficiently where the home is heated
- 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
Insulating, draught proofing and heating
Condensation happens when moisture laden air is cooled to a point where it can no longer hold all its moisture. Keeping the wall and ceiling temperatures just above this temperature will prevent condensation.
Many homes are only heated for part of the time; this can result in condensation occurring when the rooms are unheated. Keeping the whole home consistently warm will reduce condensation. This is better and may be cheaper, than having intermittent heating to higher temperatures of parts of the home.
Insulation and draught proofing will help keep your home warm and will also cut fuel bills.
- Insulate your loft. Remember to draughtproof the loft hatch but do not block the openings under the eaves
- Consider cavity wall insulation. In homes without cavity walls, it may still be possible to insulate the walls
- Draught proof doors and windows.
- Consider secondary and double- glazing of windows to reduce heat loss and draughts (but ensure that there is some ventilation available)
- Installing double glazed windows is usually not a cost effective way of reducing heating costs unless the windows need replacing for other reasons
- In very cold weather, keep low background heating on all day, even when there is no one at home.
- The heating system should be capable of adequately heating the whole home. It should also be able to heat reasonably economically and efficiently. In addition, it should be controllable so that the occupier can determine both the times and temperatures to which rooms are to be heated.
Some words of warning
- Do not block permanent ventilators
- Do not completely block chimneys. Instead, leave a hole about two bricks in size and fit a louvred grille over it (at the base of the flue, where the old fire was sited). There should also be ventilation at the top of each chimney flue
- Do not draughtproof rooms where there is condensation or mould
- Where there is a cooker or fuel burning heater, ensure that there is enough permanent ventilation in the room for the safe use of the fitting. The appliance fitting instructions will usually give this information
First steps against mould
First treat any mould you may already have in your home. If you then deal with the basic problem of condensation, mould should not reappear.
To kill and remove mould, wipe down walls and window frames with a fungicidal wash which carries a Health and Safety Executive ‘approval number’. Follow the manufacturer’s instructions precisely. Dry-clean mildewed clothes and shampoo carpets. Disturbing 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.
The only way of preventing the mould returning is to reduce the dampness (condensation).
The information and advice given in this guide is accurate, to the best of the City Council’s knowledge. However, you are advised not to rely exclusively on what we say here, particularly because legislation or government advice may have changed since the guide was created.
If you have a particular problem, you should take advice from a properly qualified expert in the relevant area or areas. The City Council will not accept liability for loss resulting from your relying on advice contained in this guide.