Condensation and Mould – Causes and Solutions

Condensation is a common problem in many peoples’ homes which can cause breathing difficulties, damage properties, reduce the temperature of a home and increase energy costs. Here then we will look at the causes of condensation and what can be done about it.

Condensation happens when the water vapor that is in the air in a house condenses onto cold surfaces. This can happen at any time of year and it can be seen in the form of misting or small droplets of water on windows or walls, ceilings, concrete floors, tiles and toilet cisterns. The appearance of any condensation or of mould is a clear sign that the building that it appears in is not adequately heated and or ventilated.

A wall could be cold enough to attract condensation for a range of reasons:

1. Walls at the back of an extension in older homes might be more exposed and thus colder.

2. Walls might be only made from 4 inch thick brick, particularly in older external toilets or coal houses that have been adapted into the main home.

3. It could be facing North and the room may be inadequately heated or not heated at all.

4. Trees, plants, alleyways or adjacent buildings can shade walls and windows meaning that they do not get heating from the sun.

5. Leaks from gutters or pipes might make part of a wall colder and might ‘seep’ through the wall.

6. Flat roofs can collect water if they are not properly drained off.

7. New houses may still be drying out.

Mould Growth

Mould spores are in the air even in ‘normal’ homes, and mould growth will occur whenever those spores make contact and germinate with damp surfaces that have become damp through water penetration or condensation. This mould will then appear as small black, or sometimes green or grey spots on the walls or other surfaces.

Water vapour is created through the normal activities expected from everyday living in your home such as breathing, perspiring, washing up, cooking food, taking baths and washing your hands, drying your clothes and burning fuels. The average family, it may surprise you to know, in fact produces a huge 20 pints of water moisture (12 litres) every day. You can limit this number a number of ways:

1. By keeping the lids on your pans when you are cooking, closing kitchen doors and leaving windows open and the extractor fans on.

2. Drying the clothes outside of your room rather than having them on airing racks inside. You should also pipe the tumble dryer’s moist air exhaust to the outside.

3. Also avoid drying clothes on radiators which will create steam very quickly.

4. Only boil as much water in the kettle as you need.

5. Running the cold water for a bath before you run the hot water. This way it won’t sit steaming in the bath. Make sure you close the door while the bath is filing up. When you are finished, open the windows wide for around an hour in order to let all the beads of water leave the room. If you have an extractor fan then turn this on as well for around an hour. Should you have a heater in your bathroom, turn this on for at least one hour before you go into the bathroom. Likewise, if you have central heating then make sure that the air temperature is no less than 21C. This is very important for young children and elderly residents with illnesses.

6. Do not use liquid paraffin or bottled gas room heaters. These are not very efficient and produce around 8 pints (5 litres) of water vapor for every gallon of fuel that the burn. The water then will end up condensing in your home.

Prevention of Condensation and Mould Growth

In 99.9% of cases, the best cure for condensation and mould is to improve your heating.

Ventilation: Ventilation is providing an escape route for moist air. As air in your home circulates, it is normally drawn out of your house through open windows, doors, vents, extractor fans, airbricks, chimneys and more, and is then replaced by fresh air instead. The outside air will always be drier that’s inside your home. If this exchange of air is poor then the air in your home will become saturated and water vapor will gather on the nearest cold surfaces. To allow your fresh air to circulate there are some things you can do:

1. Place extractor fans in shower rooms, bathrooms and kitchens. Ideally a bathroom requires an extractor rate of no less than 80 litres a second, and kitchens should have 60 litres a second. There are systems available that will remove most of the heat from extracted air and then blow it back into the room (this is known as mechanical ventilation with heat recovery) in order to prevent your home getting cold. A cooker hood is not a replacement for an extractor fan – if there is an open fuelled appliance in a room do not use an extractor fan with a rate of over 15 litres a second.

2. Open your windows wide until condensation disappears and then close them while leaving a ¼ inch gap between the frames in each room.

3. Be sure that trickle vents are opened in double glazing windows.

4. Keep your bathroom and kitchen doors shut.

5. Avoid still air pockets – these are the areas between the furniture and the external walls, or behind external walls – try to pull these items away from the walls slightly to encourage the air to circulate around them. Do not put mattresses directly on the floor and avoid over filling your cupboards and drawers.

6. Provide heated for affected rooms. For damp and affected cupboards, use an electric green house heater which will provide adequate warmth to prevent mould growth. Likewise, if there is a light fitting inside a cupboard, leaving a light on can do the same. Cut a ventilation hole in such cupboards to encourage a flow of air.

7. If you have a hot water storage tank in a cupboard then ensure that the feed and expansion tank’s lid is tight fitting.

8. If you have no place to dry your clothes then put them in the bathroom, turn on the heating in there and open the windows.

9. Buy a de-humidifier and place it near the source of the problem. This pulls moisture out of the air and leaves moisture levels at an optimum level that you set.


Warm air can hold more moisture than can cold air, so if you have your home heated well then you are less likely to get condensation. Arm air cooling during the night will cause condensation however particularly around windows in cold weather. This will then often evaporate when heating is turned on again so it’s important to heat throughout the night.

If you get condensation and mould growth during winter then you need thunderstone why and how you can reduce it.

Walls store heat, and the amount of heat stored depends on how heavy the materials are, their insulation standards and the period during which it has been heated. When external air cools down, heat is then lost from the structure into the outside atmosphere. If that heat is not replaced, then the walls will continue to get colder until they reach a critical temperature which is called the ‘dew point temperature’.

At this stage you will notice the formation of condensation and in turn this will cool down the walls further which creates a vicious cycle. This happens until you can take action.

You will notice:

* Your home, clothes and bedding are cold and damp. This may be accompanies by a moist, damp smell and you might see mould growing on furniture and in cupboards as well as on your surfaces. Wall paper might begin to peel away from the walls and particularly around windows etc.

* It will take a long time for heating to have any effect and your walls will stay cold to touch and you won’t feel warm yourself a result. This will inflate your fuel bills as you try to maintain a temperature – most heating systems use a thermostat which means they will continue to get hotter until they bring the home to a certain temperature – so the same setting will require more energy if you have reached this point.

* You will find it hard to keep warm, and particularly if you are elderly or spend a long time each day in the house.

To cure this problem you need to put more heat into the home until you heat the walls. You need to do this until the wall is hotter than the dew point. This will be expensive initially, but once they are dry it will be an investment and your heating costs will be lower.

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