Rising damp: low on the wall, with a tide mark
Rising damp comes up from the ground through masonry by capillary action, and it stops at a fairly consistent height, usually under about a metre. The giveaway is a horizontal tide line, often with salt deposits and bubbling paint below it.
The cause is a damp-proof course that has failed, was never installed, or has been bridged, most commonly by a flower bed, a new paving level or a plaster skim taken down past the DPC on the outside. Bridging is the cheapest thing on this list to fix and it is frequently the actual cause.
Penetrating damp: patchy, higher up, worse after weather
Penetrating damp comes through the wall from outside. It appears as isolated patches rather than a continuous band, it can be at any height, and it gets noticeably worse a day or two after wind-driven rain.
On this coast that usually means a south-westerly or north-westerly elevation taking rain horizontally, through cracked plaster, failed pointing, an unsealed cavity or a window detail with no drip. The repair is on the outside, not the inside.
Lateral damp: where ground is higher than floor
Where a retaining wall, a sloping site or a raised patio means the earth outside is higher than the floor inside, water moves sideways through the wall. It shows up as a damp band that follows the external ground level rather than a level tide mark.
This one needs tanking or external drainage, and it is the type most often misdiagnosed as rising damp and treated with an injected DPC that does nothing.
Condensation: worst in winter, worst in corners
Condensation is water that was already in the air inside the house, landing on the coldest surfaces. It concentrates in corners, behind furniture on external walls, and around window reveals, and it typically comes with black spot mould rather than salt staining.
It is a ventilation and heating problem, not a building-fabric problem. Extraction in bathrooms and kitchens, trickle ventilation and not drying laundry indoors will do more than any damp-proofing product.
How to tell them apart quickly
A rough field guide before you call anyone.
- Even band, low, with a tide mark and salts: rising
- Isolated patches that worsen after driven rain: penetrating
- Band that follows the external ground level: lateral
- Corners, window reveals, black spot mould, worst in winter: condensation
Why the wrong treatment keeps getting sold
Injected damp-proof courses and specialist plaster systems are a legitimate fix for genuine rising damp, and they are also a product with a sales channel. Applied to penetrating, lateral or condensation damp, they hide the symptom for a season and change nothing.
Insist on a diagnosis that explains where the water is coming from before you accept a treatment. If nobody has looked at the outside of the wall, nobody has diagnosed it.
Written by Edward Whelan, Spoednik Construction · Updated August 2026
