What is Condensation?

December, 2022

Condensation is the appearance of water on cold surfaces. It occurs where moist air comes into contact with air, or a surface, which is at a lower temperature. Condensation is most likely to appear on windows, colder parts of walls, around external door and window openings, and where ceilings and floors meet with outer walls. It can also appear in areas where air circulation is restricted, such as inside cupboards and behind furniture that is placed against an outside wall. If condensation keeps on occurring in the same place, it can sometimes cause black mould growth.

Water produced from condensation is generally noticeable where it forms on non-absorbent surfaces (i.e. windows or tiles) but it can form on any surface and it may not be noticed until visible mould growth appears on wall surfaces, often affecting stored items in wardrobes, particularly clothes, shoes etc., or affecting external walls and the corners of the ceilings.

Why does condensation occur?

Condensation is not normally a building fault. It can occur due to the moisture produced by everyday activities (such as taking showers and baths, washing and drying clothes, cooking and boiling kettles) being unable to disperse from the property due to a lack of adequate ventilation and heating. A typical family of four is likely to produce around 10-15 litres of water vapour each day, through breathing, washing and cooking.

Whilst the air in the property is warm, moisture is retained in the atmosphere. However, once the air temperature cools, the airborne moisture condenses onto surfaces and eventually will result in unsightly mould growth.

Traditionally older properties tended to be draughtier and were difficult to heat. However these drafts were beneficial as they diluted the high humidity and provided ventilation. Modern living habits have resulted in many properties having much smaller rooms and air leakage (draughts) have been reduced dramatically. Additionally, many properties remain empty during the day whilst occupants are at work and the windows are closed during the daytime. Combined with energy saving measures such as reduced ventilation and double-glazing, this provides the ideal environment to sustain condensation.

Prevention is key

Controlling water vapour levels is important as condensation occurs when excess water remains trapped in the air as a result of poor air circulation. Any signs of mould growth are an indication of presence of moisture, potentially caused by condensation, which gives a warning that heating, and ventilation is insufficient. Any mould appearing should be wiped away immediately.  Our three point advice to deal with this problem is as follows:-

1. Produce less moisture

  • Put lids on saucepans while you are cooking to reduce steam.
  • Try to avoid drying laundry directly on room radiators, or room heaters, as this produces more water vapour and cools the room at the same time. If you need to dry clothes indoors, open the window and close the door of the room where the clothes are drying, so that moisture can escape outside rather than circulate around your home. Ask yourself “Where will all the water vapour from the drying clothes go?”
  • If you use a vented tumble drier, try to make sure it is properly vented to an open window or through an outside wall. If you use a un-vented tumble dryers  then try and keep the extractor fan on and/or the window open in the same room. Tumble driers are major producers of moisture.
  • Run the cold water first when filling a bath as it could prevent steam production.

2. Stop moisture spreading through your home

  • While cooking, bathing or washing, use an extractor fan and/or open a window, and keep the door closed. Keep the extractor fan on and/or the window open for about 20 minutes after you have finished (with the door closed).
  • When condensation appears, wipe it away.
  • Provide some ventilation to all rooms, so that moist air can escape.
  • Use heating reasonably.

3. Ventilate moisture away

  • Leave trickle vents (slotted vents in the window frames) open when rooms are occupied – even in the winter when your heating is on. These vents provide constant ventilation which removes water vapour.
  • If you can, put free-standing wardrobes and other furniture against internal walls, leaving a gap between the wall and the furniture so that air can circulate around the room. Try not to overfill cupboards, wardrobes and drawers so that air can circulate around the contents. 
  • If there is no extractor fan, open the window but keep the door closed as much as possible to prevent moisture spreading. Too much ventilation in cold weather is uncomfortable and wastes heat, so all that is needed is a slightly open window – where possible, open a top hung window about 10mm.
  • Leave the curtains open and pulled back in all rooms during the day to allow air to circulate around the window, sill and window reveals.

4. Provide even heating

  • Keep your home warm to avoid cold surfaces, and remember that it can take a long time for a building to warm up.
  • If your home is unoccupied during the day, make sure the heating timer is set so that your home is warm by the time you return home. During very cold weather it is better to leave the heating on during the day to maintain an even temperature. The temperature can be set a few degrees lower while you are out and turned up when you return.
  • If you don’t usually use all of the rooms in your home, you should still keep them heated to avoid cold areas. It is better to keep all rooms heated to a low temperature than to have some rooms heated to a high temperature while others have the heating turned off.

Other helpful tips & advice

  • Good ventilation of kitchens when washing, drying clothes or cooking is essential. If there is an extractor fan use it, particularly whenever the windows show signs of misting, leaving it on until the misting has cleared. 
  • If there is no extractor fan, open the window but keep the door closed as much as possible to prevent moisture spreading. Too much ventilation in cold weather is uncomfortable and wastes heat, so all that is needed is a slightly open window – where possible, open a top hung window about 10mm.
  • After bathing keep the bathroom window open and shut the door for long enough to dry off the room. Again, if there is an extractor fan use it whenever possible.
  • In other rooms, provide some ventilation. Sufficient ventilation does not generally occur unless a window or ventilator is open for a reasonable time each day.
  • Ensure that all rooms, especially the bedroom, are ventilated at all times by leaving the windows open, particularly at night when you are sleeping.
  • Try to make sure that all rooms are at least partially heated. To prevent condensation, room surfaces need to be kept reasonably warm.

It is better to have a small amount of heat for a long period than a lot of heat for a short period. Even in a well-insulated house with reasonable ventilation, it is likely to be necessary to maintain all rooms above 10C in order to avoid condensation and when living rooms are in use; their temperatures should be raised to about 20C.

If you have a problem

If you notice mould growing in your home, you should really treat it straight away to stop it from spreading and causing more damage to your home, and our advice would be to take the following steps as soon as possible:

  • Wash down all areas of walls, window frames and sills that have mildew growth.
  • Sterilise the affected area with a suitable fungicidal wash (available from most DIY stores), following the manufacturer’s instructions. Keep checking the affected area for at least a week. If the mould reappears, wash it down again with the fungicidal wash to make sure the area is thoroughly sterilised.
  • If mould or mildew is growing on clothing or carpets, you should dry clean them. Don’t disturb mould by brushing or vacuum cleaning, as you can increase the risk of respiratory problems.
  • To prevent mould returning, make sure that you control condensation in your home.

It is important to recognise that, in recent years, our lifestyles have changed and our properties have become more susceptible to suffering condensation. By following the above advice, problems can be minimised.

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