Rising damp, penetrating damp or condensation?

Damp on a wall is not one problem. It is usually one of three, and they need different treatments — so the first job is always working out which one you actually have, not reaching for a fix.

Condensation is the most common, and the easiest to check

Condensation shows up on cold surfaces — windows, north-facing walls, the corner of a room with poor airflow — and gets worse in cold weather, especially after cooking, showering or drying laundry indoors. It is caused by moist air meeting a cold surface, not by water getting into the building from outside. Fixing it is about ventilation, not waterproofing.

Penetrating damp comes in horizontally, from a specific defect

This kind can appear at any height on a wall, and there is almost always a specific external cause behind it: a cracked render, a gutter overflowing down the brickwork, a perished pointing joint. It gets worse in wet weather and tends to follow a pattern that traces back outside. Treating it means finding and fixing that defect, not covering the inside of the wall.

True rising damp is rarer than it is diagnosed

Rising damp travels up from the ground through the wall itself, and is limited to roughly the height groundwater can wick to — usually under a metre. A lot of what gets labelled rising damp is actually one of the other two, misread. Most older buildings without a damp-proof course cope fine for decades; a sudden new patch is more likely a fresh external defect than the ground deciding to start rising.

When it is worth getting a survey

If the pattern does not obviously match one of the three, or a company has already quoted a full damp-proofing course without inspecting the wall first, that is worth a second look. A proper survey uses a moisture meter and a visual inspection to work out which type it actually is before anyone talks about treatment — see damp survey and diagnosis for how that works.

• Cold surface, worse in winter, follows cooking or showering — condensation.
• Appears at any height, worse in wet weather, traces to an outside defect — penetrating damp.
• Confined to low on the wall, in an older building with no damp-proof course — possibly rising damp, but check first.