Look at where it is, when it gets worse and what it looks like. Those three clues point to the cause far more reliably than any single reading.
Condensation forms on the coldest surfaces in the home: windows, corners of outside walls, behind furniture and on ceilings next to outside walls. It is worse in winter, first thing in the morning and after cooking, showering or drying washing indoors, and it usually brings black mould spots with it.
A leak, or rain getting in from outside, makes a patch with a definite source. It grows or darkens after rain, after a shower or bath is used above it, or when the heating is on, and it often leaves a brown ring as it dries.
Rising damp is groundwater drawn up into a wall. It only affects walls in contact with the ground, sits low on the wall, rarely more than about a metre high, and usually leaves a tide mark and white salts. It is real, but it is diagnosed far more often than it is found.
| Condensation | Leak or rain getting in | Rising damp | |
|---|---|---|---|
| Where | Cold spots: window reveals, corners of outside walls, behind wardrobes and sofas, ceilings along outside walls | Below a bathroom, round a chimney, under a window, under a gutter or downpipe, anywhere water can track | Ground floor walls only, low down, rarely above about a metre |
| When it is worse | Winter, cold mornings, after showers, cooking or drying clothes | After rain, wind driven rain, or when water is used above it | Fairly constant all year |
| What it looks like | Black mould spots, water beads on glass and walls, streaming windows | A patch with a brown edge or tide mark that spreads, soft or bubbling plaster | A tide mark with white, fluffy salts, decayed skirting boards |
| Mould? | Very often | Sometimes | Less often than people expect |
It is common to have more than one at once. A wall that is damp from rain getting in is also colder, so condensation and mould gather on it too. That is one reason a single explanation offered on a doorstep is so often wrong.
Tape a square of kitchen foil, about 30 centimetres across, tightly to the damp area and leave it for 24 to 48 hours with the room used as normal.
It is a useful first clue, nothing more. A cold wall can show both, and the test cannot tell a leak from rising damp.
Condensation is the most common cause of mould in homes. It means the air is carrying more moisture than the coldest surfaces in the room can cope with. The fix is usually a mix of ventilation, steady heating and dealing with the cold spots, and it is worth knowing which spots are cold and why. See black mould on the ceiling and bathroom mould that keeps coming back.
Water from outside or from plumbing has a source, and the source is what needs fixing. See damp patch or brown stain on the ceiling and damp patch on a wall but no leak.
Every one of those signs can also be caused by something else: a garden path or flower bed built up above the damp proof course, a leaking pipe in the floor, rain splashing off a hard surface, or salts left behind by water that has long since stopped. A high reading on a moisture meter does not settle it either. Can a damp meter prove rising damp? explains why.
If you have been told it is rising damp and quoted for treatment, read before you pay for damp proofing first.
Each cause has a different fix, and treating the wrong one wastes money while the real problem carries on. A damp proof course will not stop condensation. A dehumidifier will not stop rain getting through a wall. Mould paint will not stop a leaking shower tray. Find the cause first, then spend money once.
Vigilant Surveys is an independent damp and mould surveying practice covering East Anglia, North London and the West Midlands. We carry out no remedial work, sell no products and take no commission from anyone who does the repairs, so there is nothing to sell you afterwards.
Every survey includes thermal imaging, moisture readings against a dry control and hygrometer readings, and you get a clear written report within 24 hours of the visit. £350 for the problem areas, £450 for the whole property, fixed prices, no payment to book.
Look at where it is and when it gets worse. Condensation appears on the coldest surfaces, such as windows, corners of outside walls and behind furniture, and is worse in winter and after showers, cooking or drying clothes. Damp from a leak or rain getting in grows after rain or when water is used above it, and usually leaves a brown edge. Rising damp sits low on ground floor walls only.
Yes, and it is common. A wall that is wet from rain getting in or a leak is colder than the walls around it, so condensation and mould gather on it as well. That is why one explanation offered quickly is so often only half the story.
Not usually. Black mould is far more often caused by condensation on a cold surface. Rising damp more typically shows as a tide mark low on the wall with white salts and decayed skirting boards.
No. A moisture meter shows that one area conducts electricity more than another, not why. Salts left in plaster read high on a wall that is dry. Working out the cause takes the pattern of readings, control readings on a known dry wall, the air and surface temperatures, and a look outside.
A patch that grows or darkens after rain points to water getting in from outside: a gutter, downpipe, roof, chimney, window sill, cracked render or poor pointing. Rising damp and condensation do not follow the rain in the same way.
No payment to book. Tell me what you are seeing and I will call you straight back, usually within a couple of hours, to arrange a visit and confirm the fixed price.
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