Rising damp or condensation? How to tell the difference

Condensation: the most common kind of damp

Condensation happens when warm, moist air meets a cold surface and the moisture turns back into water. Every household puts litres of water into the air each day from cooking, washing, showers and breathing. If that moisture is not removed by ventilation, it settles on the coldest surfaces.

• Black spot mould on outside walls, in corners, behind furniture and around windows
• Streaming windows in the morning, especially in bedrooms
• Worst in cold weather and in rooms that are heated least
• Mould in wardrobes and cupboards on outside walls
• No clear tide mark or edge; the damp follows cold surfaces

Rising damp: real, but rarer than you are told

Rising damp is ground moisture drawn up a wall that has no working damp proof course. In Kent it is mostly found in older solid walled houses, and even there it is diagnosed far more often than it occurs, because several other faults leave the same tide mark.

• Damp at the base of the wall, typically up to about a metre, falling off with height
• A tide mark, often with white salts on the plaster
• Present all year, not only in winter or after rain
• Usually on walls in contact with the ground, not upstairs or on internal partitions with no ground contact
• Skirting boards and floor timbers nearby may be decayed

Penetrating damp and bridging: the things often mistaken for both

Rain getting in through a wall, and ground levels raised above the damp proof course, cause more damp in Kent houses than true rising damp. A patio laid against the back wall, a flower bed heaped up at the front, a leaking downpipe or a gutter overflowing down one corner will all wet the base of a wall and leave a tide mark.

The giveaway is usually that the damp follows the weather, or sits under a specific feature outside. Damp that gets worse after rain and eases in dry spells is coming from outside.

Checks you can do yourself

Before anybody quotes, a few checks narrow it down.

• Walk round outside. Is the ground, path or patio within two brick courses of the damp proof course, or above it?
• Look at gutters and downpipes above the damp patch, ideally while it is raining
• Note when the damp is worst: after rain, in cold weather, or all the time
• Check that bathroom and kitchen fans run, and feel whether they pull air
• Move furniture away from cold outside walls and see whether the mould behind it stops spreading

When to get a survey

If the damp persists after the simple fixes, if you are being quoted for injection or tanking, or if you are buying a house and the homebuyer report flags damp, an independent survey is worth having. We take readings at depth, measure humidity and surface temperatures, inspect outside, and say which kind of damp it is, in writing, within 24 hours. We sell no treatment, so the answer is not shaped by a sale.

Questions

Related

• Rising Damp
• Condensation and Mould
• Penetrating Damp
• Damp proofing quote check: when you do not need a DPC
• How much does a damp survey cost in Kent?
• Do I need a damp survey when buying a house?
• Landlord damp and mould duties, and Awaab's Law
• What woodworm and rot treatment costs