Penetrating damp
Penetrating damp is rain getting into your home through the walls, roof, chimney or windows. The giveaway is a patch that appears or darkens after wet weather. Fix whatever is letting the water in, and the inside usually dries out on its own.
We match you with one local specialist who can trace where the water's coming from. We don't do the repairs ourselves, and asking is free.
Where the water usually gets in
- Gutters and downpipes. Cracked, blocked, sagging or leaking at the joints, so water pours down the wall instead of away from it. The single most common cause.
- Pointing. Mortar between bricks that has worn away, cracked or shrunk.
- Render. Cracks let water in, and the render then stops it drying out.
- Roofs and chimneys. Slipped or broken tiles, failed lead flashing, cracked chimney pots or a chimney with no cap.
- Windows and doors. Gaps in the sealant around frames, or a missing drip under the sill.
- Flat roofs. Over extensions and bay windows, where felt or membrane has cracked or lifted.
How to narrow it down
Go outside after a spell of heavy rain and stand directly behind the damp patch. Look up. A dripping gutter joint, a stained downpipe or a dark band of wet brick will often show you the cause straight away.
Inside, note whether the patch grows when the wind blows from one direction. Walls facing the prevailing wind, which in most of England means south-west, take the brunt of driving rain.
How it's fixed
The repair is to the outside: clearing or replacing gutters, repointing, patching or replacing render, re-flashing a chimney, resealing a window. Some walls then benefit from a breathable water-repellent treatment. Once water stops getting in, give the wall time to dry before replastering or decorating.
If mould has grown on the damp patch, it can be cleaned off once the source is fixed. See mould removal.
What it usually costs
| Job | Typical range | Source |
|---|---|---|
| Small, localised repair | £300–£1,500 | MyJobQuote |
| Treatment including external repairs | £1,000–£5,000+ | MyJobQuote |
| Single wall, terraced house | £400–£600 | MyJobQuote |
| Single wall, detached house | £500–£800 | MyJobQuote |
| Damp proofing external walls against penetrating damp | £1,000–£3,000 | Checkatrade |
Sources: MyJobQuote penetrating damp costs (updated 8 October 2026), average £900; and Checkatrade damp proofing cost guide (last updated June 2026), figures plus VAT.
The cause sets the cost. Clearing and resealing a gutter is a small job; repointing a gable wall or replacing failed render needs scaffolding, which often costs more than the repair itself. Ask whether access equipment is included in the quote.
Facts, dates and prices on this page were last checked on 29 October 2026.
Common questions
Is penetrating damp the same as a leak?
It's a kind of leak, but from outside rather than from your plumbing. Rain gets into the walls or roof through something that has failed, and works its way in until it shows on the inside.
Should I put a waterproof coating on the brickwork?
Sometimes, but not as a first step. Fix gutters, pipes and pointing first. Some masonry creams let walls breathe and some sealers don't; on older solid walls, the wrong product can trap water inside. A specialist can tell you whether the wall needs one.
Who do I call, a roofer or a damp specialist?
If the cause is obvious, such as a broken gutter or a slipped tile, go straight to the right trade. If you can't see where the water is getting in, a damp specialist or surveyor can trace it first.
Does cavity wall insulation cause damp?
It can in some cases, for example on walls that take a lot of wind-driven rain or where the insulation was badly installed. If damp started after insulation went in, mention it to the specialist.
Will the inside wall need replastering?
Often not, once the wall has dried. If the plaster has blown, crumbled or is heavily stained, part of it may need replacing. Leave decorating until the wall is dry.
Ask for a local damp and mould specialist
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We're a matching service, not the firm that does the work. The specialist contacts you, looks at the problem and quotes you directly. Whether you go ahead is up to you.