What you need to know to prevent mould & condensation

As the days grow ever shorter and the nights longer, it's at this time we start to notice homes develop mould and condensation as a result in the change of temperature. Here's what you can do to prevent this happening in your home this winter.


Condensation occurs on cold surfaces such as windows, floors, and walls which can lead to mould. Mould can damage the decor, floor covering, clothes and bedding and can occur on the walls and ceilings. In some cases, it can cause respiratory problems and cause people with asthma further aggravation. Cases of condensation caused by buildings defects, such as new buildings which often take a long time before they are fully dried out and may need extra heat and ventilation, will be investigated immediately, however in most cases, condensation is caused by the lifestyle of the occupants.

Everyday things like cooking, washing, bathing and even breathing cause moisture, which is released into the air. The air can only hold a certain amount of water vapour - the warmer it is, the more it can hold. If this is cooled by contact with a cold surface such as mirror, a window or even a wall, the water vapour will turn into droplets of water - condensation. This is what happens when the mirrors mists up in the bathroom.

Intermittent heating causes condensation to gather as the air and surface cool.

Extractor fans, when fitted, should be used whenever water vapour is being produced, i.e. cooking, washing clothes and bathing. Doors and windows should be kept closed when using the fan and it should be left running until any mist clears from the windows. Tumble dryers (other than condensing types) for laundry should have the moist air ducted to the outside.


  • Keep all rooms warm and ventilated with an even temperature throughout
  • Keep kitchen doors closed when cooking, washing or drying clothes. Open the window or use the extractor fan where fitted
  • Keep the bathroom door closed when bathing and open the window or use the extractor fan, where fitted
  • Avoid the use of paraffin heaters and flue less gas heaters in unventilated rooms (Note that paraffin produces a volume of water equal the amount of fuel used)
  • If possible keep some heating on at all times during the cool weather
  • Move furniture slightly away from the walls to allow air to circulate behind it


  • Heat the room as described above
  • Mop up as much as possible and wipe away mould with a specialist cleaning product.
  • Open windows a little
  • Keep doors shut
  • Move furniture slightly away from the walls to allow air to circulate behind it

To kill and remove black mould, affected areas should be wiped down using a fungicidal wash (available from most DIY or hardware stores) or a diluted bleach solution. Mould should NOT be disturbed by brushing or vacuum cleaning as this can cause it to spread. It is strongly recommended that a disposable respiratory mask is worn, also available from more DIY and hardware stores, when removing any mould growth. After removing black mould, a good quality fungicidal paint can be used to redecorate the affected areas.

A checklist for the removal of mould (WHO, 2009) can be found below:

  • Have a big plastic bag ready to take away mildewed clothes, curtains, rugs and carpets for cleaning. Consider replacing a mattress or soft toy that smells and feels damp.

  • The process of cleaning will release mould spores into the air. Open any windows but close doors tightly to help prevent the spores being spread to other areas of the house. Leave the windows open during and after the clean-up activity.

  • Prepare a bucket of water, some mild detergent, such as washing up liquid or a soap used for hand-washing clothes, and some rags that can be thrown away after removing the mould.

  • Carefully wipe the mould off the wall surface with the soapy rag. Take a dry rag to wipe down and remove the moisture following the cleaning process. Put the rags in a plastic bag prior to disposal.

  • After mould removal, all surfaces in the room should be thoroughly cleaned either by wet wiping or by vacuum cleaning preferably with a HEPA filter1 to remove spores that have spread during mould removal.

Remember - warmth and ventilation help prevent condensation

For particular stubborn areas, there are products out there such as this one which actually absorb moisture preventing condensation build up and are fair inexpensive. These are great to put on the window sill and watch them work their magic over night. Or a more expensive approach but always successful one is to buy a dehumidifier which will suck all the moisture in the air so you can easily dispose of it safely.