Maintenance - Condensation

Recommendations for Tenants

It is well known that in recent years some houses and flats have suffered from condensation. Walls and ceilings, and sometimes floors, become damp and sometimes discoloured and unpleasant as a result of mould growing on the surfaces.

Why condensation occurs.

Condensation occurs when warm moist air meets a cold surface. The risk of condensation therefore depends upon how moist the air is and how cold the surfaces of rooms are. Both of these things depend to some extent on how a building is used.

The four main factors that cause condensation are:

Excessive moisture being produced in the home.
Not enough ventilation.
The temperature of the home.
Cold surfaces in the home.

When condensation occurs.

Condensation usually occurs in cold weather, whether it is raining or dry. This is because the building structure is cold, windows are opened less and any moist air cannot escape. Condensation does not usually leave a ‘tidemark’ around its edges; this type of dampness may have another cause, such as a water leak or rising damp.

Where condensation occurs.

Condensation which you can see often occurs for short periods in bathrooms and kitchens because of the steamy atmosphere, and quite frequently for long periods in unheated bedrooms. It also appears on windows, or in cupboards or the corners of rooms where ventilation and movement of air are restricted. Besides condensation on visible surfaces, damage can occur to materials which are out of sight, for example from condensation in the loft space.

What is important?

Three things are very important:

Prevent very moist air spreading to other rooms from kitchens and bathrooms, or from where clothes may be put to dry.
Provide some ventilation to all rooms so that moist air can escape.
Use the heating reasonably.

The following notes give advice on how to help avoid condensation in your home:

Reduce the moisture content of the room

Do not use paraffin or bottled gas heaters as they produce about a pint of moisture for every pint of fuel they use. Do not use your gas cooker to heat your kitchen.
If possible hang your washing outside to dry, or put it in the bathroom with the door closed and a window open. Do not be tempted to dry it on radiators or in front of a fire. If you use a tumble drier, make sure it is vented to the outside unless it is of the self condensing type. DIY kits are available for this.
Always cook with pan lids on and turn down the heat once the water has boiled. Only use the minimum amount of water when cooking vegetables. Do not leave kettles boiling.
Keep kitchen and bathroom doors closed when they are in use, even if they have an extractor fan. This will help prevent the moisture reaching other rooms, especially bedrooms which are often colder and more likely to suffer from condensation.
Ventilate your bathroom for about twenty minutes after use by opening a small top window. If fitted use an extractor fan as they are cheap to run and very effective.
Ventilate your bedroom by leaving a window slightly open at night or use trickle ventilators if fitted – even breathing contributes to condensation!
Ventilate your home for about an hour each day by opening the inside doors along with a small window downstairs and a small window upstairs which are diagonally opposite. This is called ‘cross – ventilation’ and allows air to circulate throughout your home.
Make sure that accessible windows will not cause a security problem – remember to fit security locks to ground floor windows.
Do not to ‘over-ventilate’ your home, as the temperature will drop and add to the problem.
When filling your bath, run the cold water first and then add the hot as this will reduce the steam by up to 90%.
Make sure cupboards and wardrobes are also ventilated; avoid putting too many things in them as this stops the air circulating. Pull shelves away from the back of wardrobes or if possible use slatted shelves. Drill ventilation holes in the back of wardrobes and leave space between the back of large pieces of furniture and the wall. Place floor mounted furniture on blocks to allow air to circulate underneath them. Try to position furniture against internal walls rather than against colder outside walls.
Do not draught proof rooms with a condensation problem, or where there is a heater or cooker which burns fuels such as gas. You can leave the top edge of windows and doors without draught proofing to allow air to circulate underneath.
Wipe down any wet windows and sills every morning. Wring out the cloth rather than drying it on a radiator.
If you have a freezer, it is a good idea to put it in a spare room suffering with condensation, as the heat from the compressor should keep condensation at bay.

Provide reasonable heating

Try to make sure that all rooms are partially heated. Condensation most often occurs in unheated bedrooms.
To prevent condensation the heat has to keep room surfaces reasonably warm. It takes a long time for a cold building structure to warm up, so it is better to have a small amount of heat for a long period rather than a lot of heat for a short time.
Houses and flats left unoccupied and unheated during the day get very cold. Whenever possible it is best to keep heating on, even if at a low level, but do keep a check on the meter to see how much this is costing you.
In houses, the rooms above a heated living room benefit to some extent from heat rising through the floor. In bungalows and in most flats this does not happen. Some rooms are especially cold because they have a lot of outside walls, or lose heat through a roof as well as the walls. Such rooms are most likely to have condensation and some heating is therefore necessary. Even in a well insulated house with reasonably ventilation it is likely to be necessary during cold weather to maintain all rooms at not less than 20 degrees centigrade.

Mould growth.

Any sign of mould growth is an indication of the presence of moisture, and if caused by condensation gives warning that heating or ventilation may require improvement. To kill and remove mould, wipe down the effected area with a fungicidal wash which carries a Health and Safety Executive ‘approval number’. Follow the manufacturers’ instructions precisely. Dry clean mildewed clothes and shampoo carpets. Do not try to brush or vacuum the mould away. After treatment, redecorate using a good quality fungicidal paint to help prevent the mould returning. The effect of the paint is destroyed if it is then covered with ordinary paints or wallpaper.

New buildings.

If your home is newly built it may be damp because water used in things like the plaster is still drying out. New buildings often take a long time before they are fully dried out, and while this is happening they will need extra heating and ventilation. During the first winter of use many new houses and flats require more heating than they do in subsequent winters.

British Standard 5250:1975 includes a suggested form of explanatory leaflet which can be supplied to occupiers of premises who are bothered by condensation; we have used this to help produce this information.