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Condensation - Background & Prevention

Condensation occurs for the following reasons:

Air inside the property contains water vapour and warm air is able to hold more water vapour than cold air. The warmer the air, the more moisture the air is holding. When warm air containing a lot of water vapour is cooled progressively (for instance, coming into contact with an outer wall or window), then there will come a temperature at which the air cannot hold moisture any more and then it is said to be saturated. This related temperature is known as ‘dew point’ and it is a temperature at which condensation will become visible on colder surfaces.

Black mould spores (Aspadilliac Niger) naturally occurs in the air and it is the process of wetting and drying cycles that allows it to grow progressively. Mould growths tend to form on the coldest parts of external walls, on cold surfaces such as cold pipes or tanks or in difficult to ventilate areas.

Moisture occurs from human habitation in a building. For example, a family asleep produces 1.5 - 2.0 kg of moisture, a typical day of family activity produces 2.5 - 3.5 kg, cooking 2.0 – 3.0 kg, washing and bathing 1.0 – 1.5 kg, washing clothes 0.4 – 0.6 kg and drying clothes 3.0 - 5.0 kg of moisture.

Condensation problems can therefore normally be attributable to lifestyle and it is a matter of achieving the right balance between heating, ventilation and insulation as well as reducing moisture sources to reduce these types of problem.

Chartered Surveyors’ recommendations for easing of condensation problems:

  1. Maintain a constant heat temperature in the property and avoid heating in bursts.
  2. Try to ensure that a cooker hood functions when cooking and automatic extractor fan is operational when bathing with efficient external extraction. These need to be cleaned periodically.
  3. Try not to dry laundry inside the flat. If necessary, use a condensing washing machine / tumble dryer that vents externally or condensates into a waste pipe.
  4. Try to ensure that trickle vents are open / installed at high level to the windows. However, if they are not already installed, check with the manufacturer to ensure that any guarantee applicable is not invalidated by installing trickle vents. Similarly, when it is not practical to have the windows properly open, use a secure semi open night latch, if available.
  5. Natural ventilation such as windows being opened is essential, particularly when cooking and bathing.
  6. Provide through ventilation by opening internal doors. However, when cooking / bathing, the doors to these rooms should remain closed with windows opened or efficient extractor fans operating.
  7. When redecorating over mould covered walls, clean thoroughly and use anti-fungicidal paints.