Penetrating damp

Penetrating damp is water getting in from outside and tracking through the wall, rather than rising up from the ground. It shows up as damp patches that get worse after rain. We find the source, fix it, and treat the affected wall so it dries out for good.

Brighton’s exposed coastal weather and the city’s mix of old solid-wall properties make penetrating damp common, especially on south and west-facing walls that take the brunt of wind-driven rain.

How to spot penetrating damp

Penetrating damp tends to appear as a defined patch rather than a tide mark, and it usually tracks the weather:

• Damp patches that darken during or after heavy rain
• Staining around a chimney breast, window reveal or roofline
• Blown plaster or a musty smell on an external-facing wall
• Damp that appears higher up the wall, not just near the floor

Because it follows rainfall, penetrating damp is often mistaken for a one-off leak. The water is usually finding a repeatable path in.

What lets the water in

Penetrating damp almost always traces back to a building fault rather than the wall itself. The usual sources are:

• Cracked or hollow render and failed pointing
• Blocked or leaking gutters and downpipes
• Defective flashing around chimneys and roof junctions
• Porous brickwork on exposed elevations
• Faulty window seals and sills

How we treat it

Fixing the inside without fixing the source just delays the problem. So we start outside: trace the entry point, repair it, then deal with the damage indoors. Depending on the cause that can mean repointing, render repair, sealing a porous wall with a breathable treatment, or sorting guttering. Once the wall can dry, we replaster where needed.

What it costs

Penetrating damp repair typically runs £500 to £2,500, because the price depends entirely on what’s letting the water in: a section of repointing is a world away from re-rendering a whole elevation. Our cost guide breaks it down, and your survey gives you a fixed quote.

Common questions

Is it penetrating or rising damp? Penetrating damp moves with the weather and can appear anywhere on the wall; rising damp sits low down as a tide mark. The survey confirms which you have.

Will it come back? Not once the source is fixed. Treating only the interior is what causes damp to return.

Got a patch that worsens after rain? Book a free survey and we’ll trace it.