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Penetrating damp

Penetrating damp is classified as any water that finds it s way inside from the outside. It can occur at all levels of the building but it is more prevalent higher up and south east facing walls.

Penetrating damp can be caused by the following:

  • Overflowing gutters,
  • Missing roof tiles,
  • Downspouts,
  • Leaking pipes,
  • Badly fitted windows or doors, and
  • Damaged pointing, cladding, flashing or render.
  • Cracks in the masonry,
  • Damaged water management systems,
  • Defective plumbing,
  • Broken down pipes, and/or
  • Possibly the results of increased ground levels around the walls of your property.

If air bricks are covered up, that can restrict the flow of air and trap moisture which leads to damp.

Penetrating damp can lead to the following:

  • Wet rot.
  • Mold.
  • Damp plasterwork.
  • Damp smells.
  • Frost damage to masonry.
  • Visible water damage.
  • Rooms feeling cold and uninhabitable.

Which specialist should I employ?

Problem area


Roof, guttering, roof gullies, down-piping, chimneys. Roofer
Pipes and internal drainage. Plumber
Brickwork, pointing, external drainage, windows, path and ground level reduction Builder
Plaster and other wall linings Plasterer/ Damp-proofer
Basement water-proofing Damp-proofer

Symptoms and remedies

It is not particularly easy to locate the ingress of water into your property but the problem is that it can take weeks or months for these problems to appear.

Typical symptoms of rising damp and their remedies can be found here:

Damp patches on the ceiling around your chimney breast

The flashing sealing the joint between your chimney stack and roof may be cracked or become dislodged, allowing water through the joint. You will need to refit the loose flashing or replace it with the same type if it is damaged.

A damp patch or mold forming at the top of an upstairs wall

Blocked or broken gutters will send water down your wall, and possibly saturate it. You need to clear your gutters or repair the damaged ones.

A damp patch appears on the upstairs ceiling when there is heavy rain

You could have a slipped, broken or missing roof tile or slate that is letting water come through your roof. The best option is to replace the tile or slate.

The inner side of an external wall shows signs of widespread damp, which worsens in wet weather

Old bricks can become porous and let water penetrate through the wall. You need to replace the bricks, or re-point and treat the are with exterior silicone water-repellent fluid.

Isolated damp patch on inner walls

Cracked brickwork or damaged pointing in the joins will allow water through your walls. You need to replace the damaged bricks and fill any gaps in the mortar.

A damp patch appears on the inner wall of your cavity wall after heavy rain

If your brickwork is not the issue, mortar on a wall tie in the cavity could be bridging the gap and allowing water to cross to the inner wall. The only way to solve this is to remove some bricks, inspect the cavity and chip off any mortar on the wall ties.

Damp patches around your windows

Some mortar might have fallen out of the gap between your wall and windows frame. You could try sealing any gaps with a flexible frame sealant.

Damp patch along the underside of your windows frame

Your exterior window sill should have a drip groove on the underside to stop rainwater running under it and into the wall. If the groove is filled with layers of paint, water can run onto the wall, and your best bet would be to clear it. In the event that you have no groove, you can glue and nail a hardwood strip to the understand of your wooden sill about 1.4″ from the front edge. This will stop water from reaching your wall, and you can paint it to match the sill.

There are signs of rot at the base of an external door on damp patches on the floor just inside the door

A door in an exposed position is more weatherproof if it is fitted with a clapboard. Repair the rotten parts of the wood, and fit a clapboard if necessary.