Condensation, leaks or rising damp: how to tell them apart
To tell the three types of damp apart, look at where the stain is, when it appears and what it looks like. Condensation appears on cold walls in winter. A leak appears after rain or near a pipe. Rising damp appears low down, next to the floor, and climbs up the wall.
Condensation
This is water from the air turning into droplets when it touches a cold surface. It happens when there is a lot of vapour inside the home and little ventilation.
Clues to recognise it:
- it appears mainly in the cold months;
- it shows up in corners, behind furniture, around windows and on ceilings;
- you may see water droplets on the glass or the wall in the morning;
- the stain is usually dark with mould, and the wall is damp on the surface;
- it improves when you ventilate more and heat the home regularly.
Leaks and penetrating damp
This is water coming in from outside. It can come from rain, a faulty roof or terrace, a blocked gutter, a poorly sealed window, a crack in the façade or a leaking pipe.
Clues to recognise it:
- the stain appears or grows after it rains;
- it has more defined edges, sometimes with yellowish or brownish rings;
- it is near a roof, a window, a bathroom or a pipe;
- the paint may blister and the wall may feel wet to the touch;
- if it comes from a pipe, the stain does not depend on the season or on rain.
If the stain is on the ceiling of a flat below a bathroom or a kitchen, suspect a water leak. In that case, call a plumber.
Rising damp
This is water rising from the ground up through the wall, like paper soaking up water. It happens in old walls, made of stone or brick, with no barrier to stop the water rising. It is most common on ground floors, in basements and in old houses.
Clues to recognise it:
- the stain starts next to the floor and climbs to a certain height, with a more or less horizontal line;
- the plaster goes soft, the paint peels and white crystals, known as salt deposits, may appear;
- the problem is there all year round, but tends to get worse in winter;
- the skirting board is damaged, swells or rots;
- it only appears on walls in contact with the ground.
A simple test for condensation
Stick a piece of aluminium foil or clear plastic film to the wall, sealed well around the edges, and leave it for a day or two. Then see which side the water is on.
- If the droplets are on the outer face of the film, the vapour is coming from the air in the room. It is condensation.
- If they are on the wall side, the water is coming from inside the wall. It is a leak or rising damp.
This test is only a clue. It does not replace an assessment by a professional.
Why it matters to know the cause
Each type needs a different solution. Condensation is solved mainly with ventilation, regular heating and less vapour in the home. A leak is solved by repairing the point where water gets in. Rising damp usually needs a technical assessment, because it may call for work on the plaster or on the building itself.
Painting over it without dealing with the cause is a common mistake. The paint looks good for a short time and then blisters or the mould returns.
Tip: Take dated photos of the stain over a few weeks. It helps you see whether it gets worse with rain or with cold, and it helps the professional who comes to assess it.
In many cases, the problems overlap. In an old house near the sea, for example, there can be rising damp and condensation at the same time. If you are in doubt, ask for an assessment before spending money on works.