Damp in basements and ground floors
It is the only part of a home where moisture rising from the ground is genuinely likely. But basements also condense — especially in summer, when warm outside air meets cool walls.
What it usually is
A damp band up to ~1 m from the floor, white salts (efflorescence), crumbling plaster; the same all year.
Damp walls and objects in summer, a musty smell, mould on boxes stored against the wall.
Outside ground higher than the floor, blocked gutters, water running onto the façade after rain.
What to check
- The height and shape of the patch: an even band near the floor points to rising damp.
- Whether the outside ground is higher than the floor inside.
- Whether it is worse in summer (condensation) or after rain (water ingress).
- Whether an old stone wall has a cement render — it stops the wall from drying.
What you can do today
- 01Move boxes and furniture away from the walls and store things on shelves, not on the floor.
- 02In summer, air the space early in the morning and at night, not in the heat of the day.
- 03Clear the gutters and make sure rainwater runs away from the façade.
- 04Don't paint the inside with waterproof paint: the water just climbs higher.
Guides for this room
Frequently asked questions
Warm, humid outside air comes in and cools as it touches the basement's cool walls, which are below the dew point. Water condenses on the walls and on stored objects. Airing in the heat of the day makes it worse; a dehumidifier and airing at night help.
It eases the air and the smell, but it doesn't stop ground water climbing the wall. Use it as a stopgap while you decide how to treat the cause.