Damp Walls: What’s the Problem?

Damp problems in a house can be due to a number of causes, such as rain getting through the walls or roof, moisture being absorbed from the ground, condensation settling on cold surfaces or a mixture of these. Make sure you determine the cause of the dampness before you try to cure it, otherwise you could be using the wrong remedy altogether.

1. Damp down low

If you have damp patches, bubbling paint, crumbling plaster or powdery deposits on wall surfaces close to the floor, rising damp is probably the culprit. Rising damp usually occurs in masonry walls because of the failure or absence of a damp-proof course, although poor sub-floor ventilation and bad site drainage can also be contributors.


  • Improve the drainage of the site. Make sure the surrounding ground slopes away from the building.
  • Check there’s enough room under the floorboards for moisture to evaporate from the soil below and pass out through sub-floor wall vents.
  • Install a damp-proof course. This job is best left to the professionals.

2. Condensation

If you’re not sure of the cause of a damp patch on a wall, try the foil test. Dry the wall surface with a fan heater, then tape some kitchen foil tightly over the affected area. If the surface of the foil is wet after 24 hours, you have condensation. Condensation occurs when moisture-laden air builds up inside the house. Poor ventilation and over-efficient draughtproofing are often to blame.


  • Install extractor fans or vents in kitchens, laundries and bathrooms so that moist air is expelled outside the house before it causes problems inside.
  • Don’t use moisture-producing portable gas heaters to warm cold, damp rooms.

3. Damp patches

Damp patches on walls are generally the result of penetrating damp, where water from outside gets into the brickwork through gaps and cracks. If the patches are clustered around windows and doors, then it’s likely that rain is getting in through gaps around the frames. If the damp is below the opening, it may be because there is no drip groove below a projecting sill. Any other patches of damp are most likely caused by faults in the brickwork, including cracked pointing.


  • Keep external walls, including the pointing and the paintwork, in good condition.
  • Seal the gaps around window and door frames.
  • Clear out or cut drip grooves below windowsills.

4. Leaks

Faults in the roof structure, including damaged or missing tiles, poor flashing and broken or cracked gutters and drainpipes, can be the cause of dampness in the house. They’re usually easy to spot, being located either around the ceiling or on sections of wall that line up with the external pipe work. Damp patches may also be the result of leaks in plumbing work embedded in the wall or from poorly sealed bathrooms.


  • Repair a faulty roof.
  • Deal with leaky pipes.

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