How to prevent condensation & mould in your property

During the winter months, many properties suffer from damp and mould growth due to condensation.

Causes and signs of condensation

Air can hold moisture – the warmer the air, the more moisture it can hold. If moist air is cooled by contact with cold surfaces, such as walls, windows or mirrors, the moisture condenses into water droplets, known as condensation.

Mould often occurs because of condensation. It appears as pinpoint black spots, usually on the side surfaces of external walls, in corners and in poorly ventilated spaces, such as behind cupboards and wardrobes.

Condensation control

The control of condensation requires a combination of sufficient heating, ventilation and insulation.


By introducing low level heating, the temperature of internal surfaces will rise and will reduce cooling of any moisture-laden air, as a result, the amount of condensation.

Ideally, low level background heating should be continuous, as any short bursts of heat may not result in a suitable rise in surface temperatures.


Thermal insulation, such as loft or cavity wall insulation, draught proofing and double glazing, will help to reduce the amount of heat lost from a property. This will not only help keep internal room temperatures higher, but will also help to keep fuel bills down.


Adequate ventilation is essential to allow moisture-laden air to escape from the home before condensation occurs. Extractor fans in the kitchen and bathroom can prove very effective in reducing condensation, especially when fitted with an effective humidistat control.

How to reduce condensation

  • pull wardrobes and furniture away from walls, and keep tops of wardrobes clear, to allow air to circulate
  • close doors and open windows when cooking
  • keep lids on saucepans when cooking
  • keep bathroom doors closed when bathing, and open windows slightly afterwards
  • do not dry clothes on radiators, unless ventilation is increased
  • only use Liquid Petroleum Gas or paraffin heaters in ventilated rooms, as these fuels produce water vapour during combustion

Extreme cases

In extreme cases, try the following:

  • a dehumidifier, which extracts moisture from the air, can be bought or hired
  • wipe down surfaces affected by condensation regularly to prevent mould growth
  • mould can be removed by washing the surface with a disinfectant or a fungicidal wash. This must be used in accordance with the manufacturers’ instructions.

Mould-inhibiting paints and sprays can also help to reduce the effects of condensation.

Other causes of damp

  • all accessible plumbing for leaks
  • guttering and down pipes for cracks and blockages, for example, leaves
  • overflows and waste pipes under sinks for leaks
  • possible roof leaks
  • damaged outside walls or eroded pointing
  • high garden or path levels overlapping the damp proof course

This type of damp is called penetrating damp, and generally leaves ‘tide marks’ and mould growth around the area of defect.