Wednesday, 22nd August 2018 | by: Justin Burns

What is Condensation?

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 every-day activities and some of this moisture appears as tiny droplets of water, most noticeable on windows on a cold morning. This is condensation. It can also be seen in mirrors when you have a bath or shower and on cold surfaces such as tiles or cold walls.

Condensation occurs in cold weather, even when the weather is dry. It does not leave a “tide mark” around its edges on the walls. If there is a tide mark, this dampness might have another cause such as water leaking into your home from a plumbing fault, defects in the roof, walls or damp proof course.

Condensation generally appears on or near windows, in corners and in or behind wardrobes and cupboards. Condensation forms on cold surfaces and places where there is little air movement.

Problems that can be caused by excessive condensation

Dampness caused by excessive condensation can lead to mould growth on walls 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 and the presence of mould and dust mites can make existing respiratory conditions such as asthma and bronchitis worse.

First steps against condensation

You may need to take steps to deal with condensation, but in the meantime there are some simple things you should do straight away.

Dry windows and window sills every morning as well as surfaces in the kitchen or bathroom that have become wet. Wring out the cloth rather than drying it on a radiator.

First steps against mould growth

First treat the mould already in the home then deal with the basic problem of condensation to stop mould re-appearing.

To kill and remove mould, wipe down or spray walls and window frames with a fungicidal wash that carries a Health and Safety Executive (HSE) approval number and ensure that you follow the instructions for its safe use.  These fungicidal washes are often available at local supermarkets. Dry clean mildewed clothes and shampoo carpets. Do not try to remove mould by using a brush or vacuum cleaner.

After treatment, redecorate using a good quality fungicidal paint and/or a fungicidal resistant wallpaper paste to prevent mould recurring. The effect of fungicidal or anti-condensation paint is destroyed if covered with ordinary paint or wallpaper.

But remember that the only lasting cure for severe mould is to get rid of the dampness.

What causes condensation?

There are four main factors that cause condensation.

  1. Too much moisture being produced in your home.
  2. Not enough ventilation.
  3. Cold surfaces.
  4. The temperature of your home.

You need to look at all of these factors to cure a condensation problem.

Too much moisture being produced in your home

Our everyday activities add extra moisture to the air inside our homes. Even breathing adds some moisture.

To give you some idea of how much water this could be in a day here are some illustrations.

Two people at home for 16 hours – 1½ litres.

Bath or shower – 1 litre or more per bath or shower.

Drying clothes indoors – 4-5 litres.

Cooking and use of a kettle – 2-3 litres.

Washing dishes – 1 litre.

Bottled gas heater (8 hours use) – 2 litres.

What you can do

Hang your washing outside to dry if at all possible, or hang it in the bathroom with the door closed and window slightly open or extractor fan on. Do not put washing on a radiator or in front of a radiant heater.

If you use a tumble dryer make sure it is vented to the outside or that it is a condensing dryer although even condensing dryers produce some moisture.

Always cook with pan lids on and turn the heat down once the water has boiled. Only use the minimum amount of water necessary for, for example, cooking vegetables.

When filling the bath run the cold water first and then add the hot – it will reduce water vapour by up to 90% which leads to condensation.

Try to avoid use of bottled gas heaters.

Do not use the gas cooker to heat the kitchen as this too produces moisture. (You might notice your windows misting over).

Ventilation of the home

Ventilation can help reduce condensation by removing moist air from your home and replacing it with drier air from outside.

Help to reduce condensation that has built up overnight by opening the first notch of a small window downstairs and a small window upstairs. (They should be on opposite sides of the house or diagonally opposite if you live in a flat). At the same time open the interior room doors, this will allow drier air to circulate throughout your home. This should be carried out for 30 minutes each day.

Note that you should make sure that accessible windows will not cause a security problem and to remember to close windows when you go out.

Ventilate your kitchen when cooking, washing up or washing by hand. Use your cooker extractor hood, extractor fan or open a window.

Keep kitchen and bathroom doors closed to prevent moisture escaping into the rest of the house.

Ventilate your kitchen and bathroom for about 20 minutes after use by opening a small window. In the bathroom or shower room, extractor fans controlled by humidity sensors should be fitted.

Ventilate the bedroom by leaving a window slightly open at night or using trickle ventilators if fitted.

Reduce the risk of mildew on clothes and other stored items by allowing air to circulate around them.

Remove “false” wardrobe backs or drill breather holes in them.

Place furniture on blocks to allow air to circulate underneath.

Keep a small gap between large pieces of furniture and the walls and where possible place wardrobes and furniture against internal walls.

Pull shelves away from the backs of wardrobes and cupboards.

Never over-fill wardrobes and cupboards as it restricts air circulation.

Cold surfaces in the home

Condensation forms more easily on cold surfaces in the home, for example walls, floors and ceilings.  In many cases those surfaces can be made warmer by improving insulation and draught proofing.  Insulation and draught proofing will also help keep the whole house warmer and cut fuel bills.  When the whole house is warmer, condensation becomes less likely.

Loft and wall insulation are the most effective forms of insulation. Cavity wall insulation can cause other problems of damp and advice should be sought before this type of insulation is installed.

If you install any draught proofing, observe the following guidance:

Do not draught proof rooms with condensation problems or where there is a heater or cooker that burns gas or solid fuel.

Do not block permanent ventilators or air bricks installed for heating or heating appliances.

Do not draught proof kitchen or bathroom windows.

If windows are fitted with trickle ventilators, keep these open.


The temperature of your home

Warm air holds more moisture than cooler air which is more likely to deposit droplets of condensation around your home.  Heating one room to a high level and leaving other rooms cold makes condensation worse in the unheated rooms. It is better to have medium to low level of heat throughout the house. Keeping the heating on at low all day in cold weather will help to control condensation.

If you do not have heating in every room, you could keep the doors of the unheated rooms open to allow some heat into them.

To add extra heat to rooms without any form of heating, it is better to use electric heaters, for example oil filled radiators or panel heaters, on a low setting. Do not use portable bottled gas heaters in homes suffering from condensation as they will give out a lot of moisture whilst in use.  It is usually cheaper to heat a room with electricity than bottled gas heaters.

If you have a freezer it is a good idea to put it in a space suffering from condensation, as the heat from the motor will help to keep condensation at bay.

Be careful not to “over-ventilate” your home when it is cold. It causes the temperature to drop and makes condensation more likely. It will also increase your heating costs.

General Considerations

Fitting insulation within properties to the internal surfaces can cause further work such as the need to remove electrical fittings, radiators and internal joinery and will also involve re-plastering. It is usually cheaper for the heating to be turned up and/or left on for longer.

Where ventilators are fitted in windows, these should normally be kept open, only closing them on cold or windy days when there is a draught.

Fans in bathrooms should be controlled by humidity sensors set to around 65% relative humidity so that the fan works when there are high levels of moisture.

Rising hinges can be fitted to bathroom and kitchen doors which would encourage the doors to close and this will help to retain moisture in the rooms.

In kitchens mechanical extractor fans discharge into the outside of the building should ideally be fitted, but this is not always practical due to construction of the buildings and location of boilers, as extractor fan outlets should not be within 300mm of fan assisted flues.

In bedrooms and living rooms extractor fans can be fitted that run silently at low extract levels with either pull cord or humidity sensor controlled boosters to activate high levels of extraction when moisture rises.  Extractor fans incorporating heat recovery can be obtained.

All fans should be cleaned at least once a year and where required the filter changed.

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