The information below is taken from the Association of Residential Managing Agents (ARMA) guidelines.

What is condensation?

Condensation is a situation where moisture is deposited on cooler surfaces, such as external walls of a building and frequently gives rise to the growth of mould (especially where sustained high humidity is present).

What causes condensation?

Condensation can occur naturally as a result of changes in temperature or artificially by the actions of people in the property.

In Britain, condensation is often, but not always, a winter problem particularly where warm moist air is generated in living areas and then penetrates to the colder parts of the building. In order to have condensation, moisture must be present in the air and this can come from a number of sources in the property such as:

  • Breathing
  • Cooking
  • Personal washing
  • Washing and drying clothes
  • Heating – especially paraffin and flueless gas heaters

Moisture can also be drawn from the structure of the building into the internal air; from below the floor or through the walls/ceilings. Buildings can often lack or have insufficient airbricks to allow adequate ventilation of the accommodation and structure. The effect of the moisture generated is made worse by keeping the moist air in the property. Usually in areas such as bathrooms and kitchens, the warmer air contains a lot more moisture than other parts of the building.

New homes

Materials such as plaster and mortar, which are used to build a house/flat, contain a lot of moisture which gradually dries out as the home is occupied and heated. However, this can take some time. This is why newly built homes can be especially prone to condensation. It usually takes upto 18 months for this to happen and owners may need to use more heat during that time.


This is one of the most common visual effects of condensation, apart from water droplets. It will often look like black spots although it can completely cover a surface when conditions are right. For mould growth to occur there needs to be a sufficient amount of clean water available (in relatively humid conditions) foe extended periods of time.

Mould can be removed by washing down with a bleach type solution and special paints can be applied which may help prevent growth of mould but the only permanent cure is to reduce the amount of condensation in a property.

Ways to control condensation

  • Increase ventilation – to remove moist air from the building and not allow it to come into contact with cold surfaces.
  • Increase insulation – to prevent a cold surface reaching below Due Point.
  • Maintain consistent heating – to prevent the property becoming cold.

It is unlikely that a British home can be condensation free, however by keeping your property properly maintained and thinking about your lifestyle and decoration, you should be able to live with condensation without it ruining your life. Below are some practical things that you can do to help:

  • Leave some background heat on through the day in cold weather. Most dwellings take quite a long time to warm up and it may cost you more if you try to heat it up quickly in the evening.
  • After a bath or shower, try to ventilate the room to the outside, not to the rest of the property. Opening a window or the extractor fan (and closing the door) will help.
  • When drying clothes indoors, dry them in a cool area of the property. Whilst, this will take longer, less moisture can be held in colder air and with good ventilation, the risk of ventilation is lower.
  • When people come in with wet coats, hang them outside the living area to dry.
  • Ensure any trickle vents in your windows are open.
  • Add forced ventilation/extraction to areas which produce a lot of moisture (kitchens and bathrooms). Extractor fans are available with an air moisture switch so that they operate automatically while the moisture in the air is above a set amount.
  • Consider using a dehumidifier.
  • Don’t overfill cupboards and wardrobes. Always ensure that some air can circulate freely by fitting ventilators in doors and leaving a space at the back of the shelves.
  • Do not use paraffin or LPG heaters.
  • Some decorative materials always have cold surfaces (i.e. ceramic tiles, mirrors, etc) and are well known for the formation of condensation. There is not much you can do where this occurs other than keeping the room evenly heated throughout the day or improve ventilation.
  • Some wall surfaces can also be a problem. Where the wall is papered the situation may be made worse if there are many layers of paper. All the layers should be stripped and the wall re-papered. Lining the wall with thin expanded polystyrene before you hang new wallpaper can help.