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How can you tell if it's rising damp?
In short: Genuine rising damp shows as damp and staining low on ground-floor walls, usually below about a metre, often with a tide mark and white salt deposits, and it changes little with the weather. But leaks, high ground levels, failed pointing and condensation can all look similar, so the only reliable way to tell is a survey that checks the cause, not just the wall.
The typical signs of rising damp
Rising damp is moisture from the ground drawn up through the bricks and mortar of a wall, where the damp-proof course has failed, been bridged or was never there. Because it comes from below, it has a recognisable pattern:
- Damp and staining that starts at floor level on ground-floor walls and rises to a fairly even height.
- A “tide mark” where the damp stops, often with a brown or yellow line.
- White, fluffy salt deposits on the plaster, and plaster that is blown, crumbling or hollow-sounding.
- Paint or wallpaper lifting along the bottom of the wall.
- Damp that is much the same summer and winter, wet weather or dry.
What gets mistaken for rising damp
Rising damp is real, but it is also blamed for a lot of damp that comes from somewhere else. The most common look-alikes are:
- Bridged damp-proof course. Soil, a flower bed, a path or a patio built up against the outside wall above the damp-proof course lets moisture straight past it. The damp-proof course may be fine; it just has a bridge over it.
- Leaks. A leaking downpipe, a blocked gully or a weeping pipe inside the wall can produce damp low down that looks very like rising damp.
- Penetrating damp. Rain getting in through failed pointing or cracked render. This is usually patchier and worse after rain.
- Condensation. Cold wall surfaces low down, especially behind furniture, can stay damp and grow mould from moisture in the air.
Fixing any of these is usually cheaper than a new damp-proof course, and a new damp-proof course won’t cure them.
Why a moisture meter on its own isn't enough
The meters used on most surveys measure electrical conductivity, not water directly. Salts in old plaster, foil-backed wallpaper and some paints all push the reading up, so a high number low on a wall doesn’t prove rising damp. That is why many mortgage surveys say “damp noted” and recommend a specialist.
A proper diagnosis looks at the pattern of the damp, the condition of the outside of the building, the ground levels against the wall and the ventilation inside, as well as the readings. See what a damp survey includes.
What to do if you think you have rising damp
Before booking any treatment, check the outside of the wall: is the ground, path or patio within a couple of brick courses of the damp-proof course line? Are the gutters and downpipes on that wall sound? Those are worth putting right whatever the diagnosis.
Then get the cause confirmed. Our damp survey costs £119, and that is deducted from the cost of any treatment if you go ahead with our quote. If it is rising damp, treatment means a new chemical damp-proof course and salt-resistant replastering, which we carry out ourselves.
Frequently asked questions
How can you tell if it's rising damp: FAQs.
How high does rising damp go?
It usually stays low on ground-floor walls, commonly below about a metre, because there is a limit to how far moisture can be drawn up through brick and mortar. Damp much higher than that usually has another cause.
Can rising damp affect upstairs rooms?
No. Rising damp comes from the ground, so it affects ground-floor walls. Damp upstairs is almost always penetrating damp, a leak or condensation.
Is rising damp worse in winter?
Not much. Rising damp changes little with the weather. Damp that is clearly worse in winter points to condensation, and damp that is worse after rain points to penetrating damp.
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