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What Causes Penetrating Damp?

Do I have penetrating damp

Penetrating damp is caused by water entering a wall, ceiling or floor from outside the building or from leaky plumbing.

A wide variety of exterior defects can allow water ingress. Here are some of the most common causes of penetrating damp that we encounter.

Cracks in the walls

A large enough crack in an exterior wall can allow rainwater into a building.

Cracks also have a nasty habit of growing: what starts as a thin, hairline crack can be widened by the freeze-thaw of water until it’s wide enough to let water flow freely into the walls.

We also often find cracks around the edges of door or window frames which haven’t been properly sealed or have separated due to movement of the building.

Just because a building is crack-free now doesn’t mean it’s going to stay that way.

Vibrations from nearby heavy vehicles or construction work can gradually cause cracks to form in walls, as can subsidence, where poor ground quality or foundations causes part of a building to sink into the earth, literally tearing the walls apart.

Be aware of any new cracks that appear in walls or ceilings as they may indicate a more severe problem.

Leaking roof or chimneys

Missing tiles, damaged rafters or inadequate drainage all give water a chance to seep into a building.

This water often travels along the structure before pooling elsewhere, such as the edge of walls or around light fittings, so the site where the damp is visible isn’t always the same as the site of the leak.

Chimneys are also common problem areas for damp. The point where the roof meets the chimney breast is often poorly sealed, allowing water to seep along the side of the chimney breast and down into the attic.

Another issue is that the chimney pots may have no cowls installed or the cowls have been damaged, letting water fall straight down the chimney.

Decayed pointing

Pointing (the cement or mortar used to full the joints of brickwork or masonry) which has deteriorated or of poor quality can allow rainwater to seep between the bricks.

This water can then seep deep into the walls or create cracks by freezing and thawing. Our wet British weather means that all pointing needs to be eventually replaced, but a good pointing job should last decades or more.

If you can easily remove chunks of pointing with your fingers or crumble it away with a butter knife, then your brickwork is due a repointing, otherwise the walls and the rest of the structure is vulnerable to damp problems.

Decayed pointing can also be another cause of chimney leaks.

Blocked or cracked gutters or plumbing

Pipes and gutters which move water through or away from the building can cause penetrating damp if they are blocked or cracked.

Unblocking a gutter is as simple as removing the leaves or other debris causing the blockage, while cracked gutters are easily spotted and replaced.

Leaking plumbing is more difficult, as the exact source of the blockage or breakage may be buried deep in the walls, requiring invasive building work to find the source of the problem and replace the damaged pipes.

Old copper hot water pipes are more vulnerable to breakage as the expansion and contraction can, over time, weaken the pipes or solder until they crack.

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