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Identifying and preventing damp and condensation

What Causes Damp and Condensation?

If a house is not properly ventilated, you may have problems with dampness and condensation. Problems often happen if airbricks (large bricks with holes through them) are blocked up. Airbricks are important because they ventilate the spaces above and below the floor.

If dampness is spotted quickly and treated it will usually only cause staining to your decoration. If damp is not treated straight away it can lead to more serious problems such as wet or dry rot. Treating these problems can be expensive and may involve major disruption such as the replacement of joists, floorboards, skirting and plaster.

You can improve ventilation in your home by:

  • Checking and cleaning air bricks.
  • Fitting and using an extractor fan in the kitchen and bathroom.
  • Opening windows when cooking or washing.
  • Drying clothes outside.
  • Venting tumble dryers externally.

If water gets into your home it can cause dampness. Common causes are heavy rain/snow, a leaking gutter or pipe or moisture rising up through the floors or walls. A damp proof course (DPC) can prevent damp in your home. However, dampness around the skirting boards can often be a sign that there is a problem with your DPC and if so, your DPC will need to be re-done.

Dampness On The Ceiling

If you spot damp on the ceiling or at the top of walls, then this is a sign of a leak from above. The leak may also be coming from the flat above if there is one. If this is the case, you should discuss with your neighbour in the first instance and if necessary, contact Environmental Health.

Tel: 0300 123 0900 /


Blocked gutters can lead to water spilling over, leaking into your home and causing damp. Leaves often cause blockages but a leaf guard can prevent this happening. You can buy a leaf guard at a DIY store. You should check your gutters at least once a year.


'Flashing' is the name of the protective layer (usually made of lead or zinc) that covers the joints where the roof and chimney meet. You should check these joints regularly to ensure that they are not damaged.


Roof slates can break or come loose, especially in bad weather so you should check them regularly. After a storm or bad weather, check the area around the house for fallen slates.

Down Pipes and Over Flows

If these are leaking they will need to be repaired to prevent any dampness. Contact a local plumber.

Damp Coming Up From The Floor

If you have damp coming up through the floor or lower walls, there could be a number of causes:

  • Soil at high level or above the DPC.
  • Broken or no DPC.
  • Leaks from plumbing and central heating.
  • Leaks from gutters, down pipes and over flows.
  • Blocked drains.

Damp In The Middle Of The Walls

This could be caused by three things:

  • Hidden pipe work that has developed a leak.
  • Something blocking the cavity in the wall, allowing damp to cross from the outer wall to the inner.
  • Dampness in an unused chimney flue.

You can check for plumbing problems using a pipe detector. Also check if the pointing between the bricks or stones is missing or crumbling. If you think the problem is in your chimney flue, you can put a plaster vent in the blocked up fireplace serving the chimney. If you can't find the source of the problem, or are unsure what to do, then you should call a builder for advice.

Dry rot

Dry rot is a fungus which lives off wood and can move through brick and stone walls. It forms fruiting mushrooms which can produce spores, and can spread quickly if is has a source of damp wood to food off. Dry rot can be controlled by stopping the source of the damp, such as roof leak, ventilation problems or plumbing leaks. Affected wood needs to be replaced with properly treated new timber. Dry rot is destructive and expensive, and should be treated as soon as possible. It can stay dormant for long periods, so affected timber and plaster work must be stripped out.

Chemical fungicides must be used to treat walls and should go at least a metre over the effected area.

Wet rot

Wet rot is caused by timber repeatedly getting damp and decaying, and usually a fungus is present. Once the cause of the damp is stopped, all that needs to be done is replacing the damaged wood. Keep timbers dry at all times, if the structural timber in your house (roof joists or floors) is affected by rot, you should seek expert advice as soon as possible.

How To Prevent Damp

  • Clear soil away from the walls of your house.
  • Repair or replace your existing DPC.
  • Repair damaged gutters, down pipes and over flows.
  • Slope paths and hard surfaces away from the house and drain surface water into a drain or sewer.
  • Make sure there are no cold corners or cold cupboards.

If you are still unsure you should seek expert advice.

What is Condensation and What Causes It?

If you find water on the inside of your window or on other cold surfaces, it is likely to be condensation. You may also find black mould on the walls or blue/green mould on leather or wood. If you have mould, it is usually found in cold corners or cupboards.

Condensation is caused when warm moist air meets cold surfaces. It happens mainly in winter when the building is cold and windows are not open as much. Reducing the moisture content in the air can help prevent condensation. One way of doing this is to make sure your home is properly ventilated, but a combination of heating and ventilation is the best way to prevent condensation.

How Do I Get Rid of Condensation?

  1. Increase the ventilation in your home by opening windows regularly or using window and wall vents.
  2. Stop warm air hitting the windows by hanging heavy close-fitting curtains and/or using plastic film double glazing available from DIY stores.
  3. If windows frames are rotting and can't be repaired, consider getting double glazing fitted.
  4. Check if your walls are cold or feeling clammy. This could mean you have too little insulation in the walls. This will also add to your heating bill.
  5. Check that you have the right kind of heating. An energy advice survey will help with this. Contact the Energy Agency for advice and support to improve the energy efficiency of your home. Tel: 01292 521896 or email:
  6. Don't not use portable paraffin or cylinder gas heaters which will create more water vapour.

There are many causes of dampness and condensation in your home. It is important to find out how and why problems are happening so you can tackle them and stop it happening again. This leaflet contains only general information on how to prevent, identify and treat dampness and condensation.

Who Could You Contact For Assistance/ Advice

  • A Plumber
  • A Builder
  • An Architect or Surveyor
  • A Dampness Specialist Company
  • Housing Policy and Strategy Team: Tel: 0300 123 0900