Do this first
- Look at what is directly above it. A bathroom, a kitchen, another flat, a loft, a flat roof, a chimney breast, or an external wall. That single fact sorts most of these before anyone tests anything.
- Isolate the electrics for that area if the damp is near a light fitting, and leave them off.
- Mark the edge in pencil and date it. Then photograph it.
- Keep a weather note for a fortnight. Two lines a day: whether it rained, and whether the patch grew. This costs nothing and it is the most decisive test available to you.
- Read the meter with everything off for thirty minutes, and the boiler gauge cold on two mornings.
- Check the loft if you have access and it is safe to do so: staining on the underside of the roof, a wet cold water tank, a dripping overflow, or daylight where there should not be any.
- Do not redecorate, and do not let anyone strip plaster before the weather correlation is established.
Plumbing, rain, or condensation
These three account for nearly every damp ceiling, and the difference between them is decided by timing and location, not by how bad it looks.
| Pattern | Cause | Who deals with it |
|---|---|---|
| Under a bathroom, kitchen or another flat; present in dry weather | Plumbing leak | Leak detection and repair |
| Top floor, under a roof, chimney breast or parapet; appears with rain and fades after | Roof, flashing, pointing or rainwater goods | Roofer, or the freeholder in a block |
| Black spotted mould in a cold corner or along a wall-to-ceiling junction, worse in winter, no water history | Condensation | Ventilation, extraction and background heat |
| Under a loft with a cold water tank | Tank, its overflow, or a burst feed in the loft | Plumbing |
| Around a soil stack or waste run, only when something above drains | Drainage, and often communal in a block | Managing agent, or us on the branch |
Condensation is diagnosed and dismissed too casually in both directions. The tells are real: it appears on the coldest surfaces, at junctions and in corners, behind furniture, on north-facing walls, it is worse in winter and in rooms that are heated intermittently, and it grows mould rather than a brown tide ring. A leak stains brown because it carries dissolved material with it; condensation grows black spots because it feeds mould on a cool surface. If the meter and the gauge are both static and the patch tracks the seasons rather than the weather, you are looking at ventilation, and no detection visit will change that answer.
A missed chimney is the other common trap. A disused chimney breast on an upper floor can deliver rain into a ceiling a long way from the stack, and the patch appears in dry weather too, because saturated brickwork keeps releasing moisture for days. If the patch is brown and ringed rather than diffuse, a water stain on a ceiling explains how to read it, and if the room above belongs to someone else, start with a leak from the flat above.
What the repair involves
On the plumbing cases, moisture mapping establishes the true wet area, thermal imaging follows heated pipe runs and finds the evaporative cooling around a leak, and pressurised circuits are isolated and tested so the source is attributed rather than assumed. Tracer gas is the last resort and the one that finds pipes nothing else can see. The report that comes out of it names the source, which is what an insurer needs and what settles an argument with a neighbour or an agent.
The repair then covers both the cause and the ceiling: pipework remade, then blown board cut out, the void dried, reboarded, skimmed and decorated across the whole ceiling. That is ceiling leak repair end to end. Where the answer turns out to be rain or condensation, we say so, and you have not paid for a repair you did not need, because of the no find, no fee position on detection.
When it is not us
- It appears with rain and fades without it. Roofer, or builder for pointing and render. In a block, the roof and external walls are almost always the freeholder's.
- Black mould, cold corner, winter only, static meter. Ventilation, extraction and heating pattern. Worth fixing properly, but not by a leak specialist.
- A chimney breast that is damp in dry weather after heavy rain. Flashing, a missing pot cover or an unventilated flue: a roofer or a chimney specialist.
- A shared roof, riser or stack in a block. Report it in writing to block management; you cannot commission work on common parts.
- You rent. Report it in writing. The structure and exterior, including gutters and external pipes, are the landlord's to keep in repair, and so are the water and sanitation installations.
- Nothing has changed in a fortnight and every reading is static. Redecorate and keep the photographs.