Is It Rising Damp, Penetrating Damp or Condensation?

Rising damp comes up from the ground and shows as a tide mark low on the wall, at a fairly even height, often with a white salty deposit. Penetrating damp comes in through the wall from outside and appears as a patch that gets worse after rain, at any height. Condensation forms on cold surfaces, in corners and behind furniture, and is worse in winter. They look similar but need completely different fixes, which is why treating the wrong one is the most common reason damp comes back.

Why it matters which one you have

The three are treated in completely different ways. Injecting a damp course does nothing for condensation, improving ventilation does nothing for a leaking gutter, and repointing a wall does nothing for damp rising from the ground. This is why so much damp work fails. Someone treats the wall without working out which type it is, it dries and looks solved, and the same patch is back within a year or two because the actual cause was never touched.

Rising damp

- Comes up from the ground through the base of the wall where the damp proof course has failed, been bridged, or was never there. - Shows as a tide mark low on the wall, usually no more than a metre up, at a fairly even height along the run. - Often leaves a white salty deposit as ground salts are carried up and left behind, and the plaster may bubble and blow. - Stays fairly constant rather than getting dramatically worse after a single rainfall.

Penetrating damp

- Comes in horizontally through the wall from outside, rather than up from the ground. - Appears as a patch at any height, wherever the fault is, not just low down. - Gets noticeably worse during and after rain, then eases in dry spells. - Usually traces back to a specific external fault, such as cracked render, failed pointing, a blocked or leaking gutter, a slipped tile or failed flashing.

Condensation

- Forms when warm, moist indoor air meets a cold surface, rather than coming from outside at all. - Shows in corners, on cold external walls, around windows and behind furniture where air does not move. - Is worse in winter and in rooms that produce moisture, such as kitchens, bathrooms and bedrooms. - Often comes with black mould spots rather than a tide mark, and is about ventilation and heating as much as the fabric of the building.

How a proper diagnosis works

The reason we survey the outside as well as the inside, including the roof by drone, is that these three overlap and disguise each other. A cold, wet wall caused by penetrating damp also attracts condensation, so you can have two at once. A proper diagnosis checks the damp course, the ground levels, the render and pointing, the gutters and downpipes, the roof and flashing, and the ventilation, then tells you which one, or which combination, you are actually dealing with before anything is treated.

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