What condensation looks like
Condensation forms when warm, moist air from cooking, showers, drying clothes and breathing meets a cold surface. It is worst in winter and in rooms that are poorly heated or ventilated.
- Water droplets on windows and window reveals, especially first thing in the morning
- Black mould spots in corners, behind furniture, on ceilings and around windows
- Damp patches with no clear edge that can appear on any floor of the house, including upstairs
- A musty smell and mould on clothes or shoes kept in wardrobes against outside walls
What rising damp looks like
Rising damp is ground moisture drawn up through masonry when the damp proof course (DPC) is missing, has failed or has been bridged, for example by raised soil, a patio built too high or render taken down to ground level. It only affects ground floor and basement walls.
- A horizontal tide mark on internal walls, usually up to about one metre above the floor
- Crumbling or salty plaster and white, fluffy salt deposits on the wall surface
- Rotting skirting boards and floor timbers along the affected wall
- Peeling paint or lifting wallpaper at low level only
Quick checks you can do yourself
Look at where the damp is and when it is worst. Damp that is high on walls, on ceilings, upstairs or worst in cold weather points to condensation. Damp that sits low on ground floor walls with a tide mark and salts points to rising or penetrating damp.
Check outside too. If the ground, a path or a flower bed is above the level of the DPC (usually a line of slate or plastic two or three bricks above ground), it can bridge it and let moisture past.
Why a proper diagnosis matters
Hand-held moisture meters are designed for timber and can give high readings on walls because of salts or foil-backed plaster, so a meter reading on its own does not prove rising damp. A thorough survey looks at the building outside and in, checks ground levels, gutters and pointing, and where needed takes samples to measure the moisture actually in the wall.
Treating condensation with a chemical DPC will not work, and treating rising damp with a dehumidifier will not fix it either. Paying for the right diagnosis first is the cheapest route to a lasting fix.
Common questions
Can condensation cause a tide mark?
Rarely. Condensation usually causes patchy damp and black mould rather than a clean horizontal line. A low-level tide mark with salts is more typical of rising or penetrating damp.
Is rising damp common?
Genuine rising damp is less common than many people think. Condensation and penetrating damp from leaks, gutters or high ground levels cause many of the problems that get blamed on rising damp.
Will a dehumidifier fix rising damp?
No. A dehumidifier reduces moisture in the air, which helps with condensation, but it does not stop moisture coming up through the wall from the ground.