Condensation and Mould

What is Condensation?

Condensation and mould growth is caused by water, which has “condensed” from air on contact with a cold surface that allows mould to grow.

Air contains water vapour in varying quantities, as warm air holds more water than cold air. Air is saturated when it cannot contain any more water vapour at the existing temperature; under these conditions it is said to have a relative humidity (RH) of 100%. If the temperature of the air falls until saturation point occurs the air is at a critical temperature at which it cannot hold any more water – this temperature is known as the dew point. Any fall in temperature will result in water vapour condensing as liquid water.

Conditions for Condensation

Moisture generated within homes by domestic activities is the primary cause of condensation. Warm moist air is produced in relatively large quantities, which can result in up to 6 litres of water per day in a 2 person home. Condensation is found more often in kitchens and bathrooms. Warm moist air can also spread to cooler parts of the house and condense on any cold surface.

The effect of moisture generation is increased by the way houses are ventilated – it is possible to avoid condensation by providing adequate ventilation. Up until the 1960’s, there was natural ventilation in many homes because of the lack of double-glazing, poorly fitting windows and doors, and open fireplaces.

Contemporary living has almost eliminated natural ventilation with the use of double-glazing, draught excluders, fitted carpets and the removal of open fireplaces. The ideal background ventilation rate in a typical home to prevent condensation and mould growth is about one air change per hour. This has created ideal conditions for condensation to occur.

In poorly insulated homes, condensation is also likely to occur more often as there is greater heat loss. This can result in internal wall surface temperature being lower than the air temperature causing condensation.

Mould Growth

Mould will appear on any damp surfaces such as plaster, wallpaper and timber and is usually associated with condensation problems. It causes issues with appearance (unsightly growths of various colours – greens, yellows, pinks, black, grey or white), odour (musty and damp), health concerns and poor hygiene.

Conditions for moulds to develop exist in cold areas of a home. Moulds are fungi from several groupings in the fungal classification system.

There are three principal features common to the broad range of mould fungi:

  1. They have simple food requirements and are able to exist on non-nutrient materials such as plaster and brick, which have traces of contaminating organic matter.
  2. They produce vast numbers of spores, which allow rapid adaptation to particular environments. Mould spores are always present in large numbers in the outside air and easily find their way inside buildings.
  3. They grow very quickly under suitable conditions.

Mould spores can have a huge impact on indoor air quality. In damp buildings toxigenic as well as allergic moulds may impact on the respiratory and general health of the occupants., and mould spores can lead to allergic reactions like coughing, sneezing and eye irritation.

The Remedies

1. Produce less moisture

Some ordinary daily activities produce a lot of moisture very quickly:

  • Cover pans and do not leave kettles boiling to reduce the amount of moisture produced when cooking.
  • Put washing outdoors to dry if you can. Alternatively, dry washing in the bathroom with the door closed and a window open and/or an extractor fan on.
  • Try to limit moisture production in bathrooms and kitchens.
  • Try to limit moisture movement from potentially damp areas by keeping doors closed.

2. Ventilate to remove the moisture

  • Keep a small window ajar when someone is in the room.
  • Ventilate cupboards and wardrobes. You should try to avoid overfilling them as this stops the air circulating.
  • Ensure windows are open wide enough to provide adequate ventilation in the kitchen when cooking and/or washing up and in the bathroom when bathing and/or drying clothes.
  • Keeps windows open slightly all year round. Ensure they are open in winter to create ventilation and decrease the difference between the external and internal temperature and/or moisture levels.
  • Create cross ventilation by opening windows on opposite sides of the home.
  • Make sure you have a working extractor fan in the kitchen and bathroom if there is no window.
  • Leave space between the back of the wardrobe and the wall to allow air to circulate behind furniture.
  • Consider putting floor-mounted furniture on blocks as this will allow air to circulate underneath.
  • Where possible, you should position wardrobes and furniture against internal walls rather than against outside walls.

3. Heat your home a little more

  • In cold weather the best way to keep rooms warm enough to avoid condensation is to keep low background heating on all day. This is very important in flats and bungalows where the bedrooms are not above a warm living room.
  • Close kitchen and bathroom doors when these rooms are in use to stop moisture reaching other rooms.
  • Keep the heating on low even if the home is unoccupied during the day, particularly in cold weather.
  • If damp is severe, a dehumidifier may be beneficial. You should ensure that you seek advice before buying one, as units are expensive.
  • Smaller areas like cupboards can be kept dry using calcium chloride crystals, which suck moisture out of the air but will need to be replaced relatively frequently.

Removal of Black Spot and other moulds from walls affected by Condensation

In the first instance, small patches of mould can be wiped off. You can use either a weak solution of household bleach or a product such as Mr Muscle Black Spot mould remover, which contains a fungicide which should help prevent the formation of mould. If problems re-occur or persist please report it.