Condensation occurs when water vapour in the air inside the house condenses on a cold surface. It can occur at any time of the year and is seen as misting or droplets on windows, walls, tiled areas, concrete floors and toilet cisterns.
A wall may be cold and attract condensation for several reasons:
- Walls to the back addition of older houses are more exposed and so may be colder.
- It may only be a 4 inches thick brick wall, especially where an old external toilet or coal house has been demolished or incorporated into the main house.
- It may be facing north or the room may be unheated.
- A leak to a gutter or pipe may make part of a wall cooler.
Mould growth occurs when mould spores germinate on contact with surfaces that are damp through condensation. The mould takes the appearance of small black spots on the wall or window surface.
Water vapour is created by normal, everyday living in your house such as breathing, perspiration, washing, cooking, bathing, drying clothes, and burning fuel.
The average family produces 20 pints of moisture every day. You can reduce this by:
- Keeping lids on pans when cooking, keeping the kitchen door closed and leaving the window open.
- Drying clothes outside or piping the tumble dryer's moist exhaust air to the outside.
- Running the cold water for a bath before the hot water. Leave the bathroom door closed whilst the bath is filling to reduce the spread of steam. When you have finished, open the window wide for an hour or so, or until the last beads of moisture have disappeared from the windows and walls. If there is an extract fan in this room, leave the window closed and leave the fan running for an hour or so.
- Not using liquid paraffin or bottled gas room heaters. These produce 8 pints of water vapour for every gallon of fuel burned.
Remedies for condensation and mould growth
This is the normal escape route for moist air. As the air in your house circulates, it is drawn outside through open windows, doors, extractor fans, air bricks and chimneys and is replaced by fresh air. If this exchange of air is prevented the air in the house will become saturated and will condense on the nearest cold surface. To allow air to circulate and be exchanged for fresh air you should consider some of these:
- Fit extractor fans to shower rooms, bathrooms and kitchens. Bathrooms require an extract rate of not less than 80 litres per second and kitchens 60 litres per second. A cooker hood is not an extractor fan.
- Open all windows wide until the condensation disappears and then close them, leaving a 1/4inch (5mm) gap between the sash and the frame in each room.
- Ensure that trickle vents are open in double glazed windows.
- Keep bathroom and kitchen doors shut to prevent moist air circulating to the rest of the house.
- Avoid still air pockets - areas between furniture and external walls, and behind heavy curtains will encourage condensation to form, because there is no circulation of warm air to warm the wall and furniture. If it is not possible to put the furniture against an inside wall, leave a gap of at least 3" to 4" (75mm to 100mm). Do not over fill wardrobes, cupboards and chests of drawers.
- Provide heating in the affected rooms. In damp affected cupboards, an electric green house heater can provide sufficient warmth to prevent or reduce mould growth. Similarly, if there is a light fitting within the cupboard, leaving the light on can do the same. (Make sure that there is a large gap between the bulb and any flammables).
Warm air can hold more moisture than cold air so if your house is heated you are less likely to suffer from condensation. Warm air cooling in the night will still result in condensation, especially on windows during cold and wet weather. Most of this will evaporate as heating is turned on again in the morning and windows are opened.
If you suffer from condensation and mould growth on your external walls during the winter, it is important to understand why, and what you can do to prevent, or at least, reduce it.
Your walls store heat. The amount of heat stored will depend upon how heavy the materials are, and the period for which it has been heated.
As the external air cools down, heat is lost to the atmosphere. If the heat is not replaced quickly enough, the walls will continue to cool until they fall below a critical temperature, called the "Dew Point Temperature".
At this stage, you will notice that condensation will begin to occur.
The formation of condensation cools the wall even more, resulting in even more condensation occurring. This will continue happening until you do something about it.You will notice that:
- Your house, clothing and bedding will feel cold and damp. There will be a musty smell.
- It takes a long time before your heating begins to take effect, your walls stay cold to the touch and you will not feel properly warm.
- Your fuel bills will increase substantially.
- You will find it more difficult to keep yourself warm, especially if you are elderly, ill, or spend a great part of your day in the house
Loft insulation, wall insulation and double glazing will help you to keep the heat in your house longer, walls are warmer and the chances of damaging condensation are greatly reduced. However, these measures will not cure condensation and mould growth by themselves. It is essential that you ensure that you heat and ventilate your home properly.
Mould growth is a result of condensation and can be dealt with quite easily:
- Ensure that your home is adequately heated and ventilated.
- Wipe off any condensation that occurs on walls, windows and window reveals.
- Wash mouldy areas with a mixture of bleach and water (one egg cup full to a pint of water).
- Use a paint that contains a fungicide when re-decorating. (These products are not effective if over-painted with ordinary paints or covered over with wall paper).
- Mouldy clothes should be dry- cleaned.
- Carpets should be professionally shampooed.