Identifying damp

Rising damp

Rising damp is ground water drawn up through masonry by capillary action. Look for wetness at the base of walls that fades higher up, with a tide mark, plus decayed skirting, salt-stained or crumbling plaster, peeling paint and decayed timber floors.

Causes include ground raised above the damp proof course, or a failed course. It is steady all year round and does not follow the weather.

Penetrating damp

Penetrating damp is rainwater getting in through walls or the roof. You will see patches on ceilings and walls, and wet around window frames.

Causes include blocked gutters, defective pipes, worn render or mortar, and damaged roof coverings. It shows up after heavy or wind-driven rain, and often dries out a little in a dry spell.

Condensation and mould

Condensation shows as beads of water and mould on cold surfaces, such as walls and window reveals. You may see stained curtains and notice a musty smell. It is worst in winter in poorly heated, ventilated and insulated homes.

Cooking, showering and drying laundry indoors put moisture into the air. Mould on cold walls is usually condensation, not rising damp. A damp proof course will not cure it.

Check the pattern

A moisture meter alone cannot tell the three apart. Look for a pattern instead:

• Height: low on the wall points to rising damp; higher up or on ceilings points to penetrating damp or a leak.
• Season: worse in winter suggests condensation.
• Weather: patches that follow rain point to penetrating damp.
• Position: corners, window reveals and behind furniture point to condensation. Take photos on different days and in different weather, and note the date. A record of how the marks change helps a surveyor, or your landlord, work out the cause.

Which part of the home is affected?

Ground-floor walls, skirting boards and timber floors suffer most from rising damp. Top-floor ceilings, chimney breasts and walls under window sills suffer from penetrating damp. Bathrooms, kitchens, bedrooms and north-facing rooms are the usual condensation spots.

Our fuller damp proofing page has problem guides for walls, bathrooms, ceilings, bedrooms and skirting boards.

Things mistaken for damp

A plumbing leak can look just like rising or penetrating damp, so a surveyor should rule it out. In the loft, damp timber can also bring woodworm, so see our guide to woodworm if you find small holes.

What to do next

If you cannot tell which type you have, book an independent survey with a damp specialist before paying for any treatment. Many jobs need a gutter or ventilation fix rather than injection. For condensation, the DIY guide shows what you can do yourself, and prices are on the cost page. Social tenants have rights under Awaab's Law.