If the loft above a ceiling stain is dry, the water is coming from inside the house. A bathroom above is the most common source, followed by a heating or supply pipe in the floor void and condensation on cold pipes. A stain that is dry and not growing may be old. A thermal camera shows which it is.
You spotted the brown ring on the ceiling, went up the ladder with a torch expecting a slipped slate or a drip from a felt tear, and found nothing. The insulation is dry. The timbers are dry. The tank is not overflowing. A relief and a puzzle at once, because the stain is still there and you still do not know what made it. This guide goes through what is usually above a water stain on a ceiling when the roof is not to blame, and how to work out which one you have.
What a dry loft actually rules out
A dry loft tells you the water did not come through the roof covering, at least not recently. Check two things before you climb back down. First, look directly above the stain rather than around the hatch. Water from a roof can run along a rafter and drop a long way from where it got in, so lift the insulation over the stained area and feel the plasterboard from above. Second, think about timing. A roof leak only runs when it rains, so a stain that grew during a dry spell takes the roof off the list.
If the loft really is dry above the stain, the water came from inside the house. That is usually better news, because internal sources are easier to trace than a roof and are normally covered by buildings insurance as an escape of water.
What is usually above the stain
Stand under the stain and work out what room and what pipework sit directly above it. In most homes the answer is one of the following.
A bathroom or shower room
This is the most common cause of a ceiling stain we see across Cornwall. The sealant around a bath or shower tray fails, water runs down the outside of the tray or bath panel, soaks into the floor and appears on the ceiling below. A shower waste trap, a bath overflow or a toilet pan connector can all do the same. The clue is a pattern: the stain darkens or feels damp within an hour of someone showering, and it is dry by the following evening. Holiday lets show it most clearly, because the ceiling goes through a wet week and a dry week with each changeover.
A heating or hot water pipe in the floor void
Radiator pipework and hot water feeds run between the joists above a ground-floor ceiling. A weeping compression joint or a pinhole in a copper pipe drips steadily onto the plasterboard, and the stain grows slowly whether anyone is using the bathroom or not. The boiler pressure gauge is your friend here. If it keeps dropping and you have no visible drip anywhere, the void above the stain is a strong candidate. Our guide on why a boiler keeps losing pressure explains how to read it.
A cold water pipe sweating in the void
Not every stain is a leak. A cold mains pipe running through a warm floor void collects condensation in humid weather, and the drips land on the plasterboard just like a leak would. This tends to show in summer, in kitchens and bathrooms, and near an uninsulated pipe. It does not move the water meter and it does not affect the boiler. It is still worth insulating the pipe, because a plasterboard ceiling that gets wet every summer will eventually fail.
An old stain that has already dried
A brown ring with a sharp, dark edge that has not changed in months may be the mark of a leak that was fixed years ago and never painted over. Mark the edge lightly in pencil, date it, and check again in a fortnight. If it has not moved and it feels dry to the touch, it is history. Stain block and a coat of emulsion will finish the job.
| What you notice | Most likely cause | What to do |
|---|---|---|
| Stain darkens after a bath or shower | Seal, tray, waste or overflow in the bathroom above | Run the shower for ten minutes and watch the ceiling |
| Stain grows slowly, boiler pressure drops | Heating pipe leaking between the joists | Note the gauge daily, book a trace |
| Damp only in warm, humid weather | Condensation on a cold pipe in the void | Insulate the pipe, improve ventilation |
| Dry, sharp-edged, unchanged for months | Old stain from a repaired leak | Pencil the edge, wait two weeks, then paint |
Reading the stain itself
A ring with a darker rim is water that soaked outwards and dried from the edge inwards, which points to an intermittent source such as a bathroom. A patch that is uniformly damp with no dry rim is being fed continuously, which points to a pipe. A soft or sagging feel means the plasterboard is holding water now, and if it starts to bow read our guide on a ceiling bulging with water before it lets go. A stain that has crept towards a light fitting needs the electrics considered too.
Tests you can do this evening
- The shower test. Run the shower for ten minutes with someone watching the ceiling below, then run the bath tap into the overflow for a minute. If the stain darkens, the bathroom is the source.
- The pressure test. Note the boiler pressure when cold. A sealed system usually sits around 1 to 1.5 bar. Check it each morning for a week. A steady fall with no visible drip means the heating is losing water somewhere hidden.
- The meter test. Turn off every tap and appliance and watch the water meter. Movement with nothing running points to a supply pipe leak, which can sit in a floor void just as easily as under a slab.
- The pencil test. Outline the stain, date it and photograph it. Growth over a week is a live source. No change is an old one.
How a thermal camera reads a ceiling
A thermal camera does not see water. It sees temperature, and water changes the temperature of whatever it touches. Wet plasterboard is cooler than dry plasterboard because moisture evaporates from its surface, so a live stain shows as a cold shape on the ceiling that is often larger than the visible mark. A leaking hot pipe shows as a warm line running between the joists, usually with a bright spot where the escape is. A sweating cold pipe shows as a cool line with no warm bloom at all.
That is why a thermal survey answers this question so well. Within a few minutes it shows whether the water is still arriving, roughly where it is arriving from, and whether the source is hot or cold. Moisture readings across the ceiling confirm the picture, and for a pressurised pipe acoustic listening can narrow the spot to a small area. Our water leak detection service combines these so the ceiling is opened once, in the right place, rather than in three exploratory holes.
Repairing the ceiling
Fix the cause first, then let the plasterboard dry fully before anything cosmetic. Board that has been wet for weeks often needs replacing rather than painting, and painting too early traps moisture and brings the stain back. When the ceiling is dry, use a stain-blocking primer before emulsion. If the water came from a heating or supply pipe, your buildings policy will usually cover the damage and the cost of finding the leak under trace and access. Our article on how to claim on home insurance for a water leak walks through the claim in order.
Whether the house is a slate-roofed terrace in Truro or a granite farmhouse near Launceston, a ceiling stain with a dry loft has an answer inside the building. We provide leak detection across Cornwall and will tell you plainly if the stain turns out to be old, condensation, or a leak that needs fixing.
Frequently asked questions
Can a ceiling stain appear with no leak at all?
Yes. Condensation dripping from a cold pipe in the floor void wets plasterboard just like a leak, especially in humid summer weather. An old stain from a leak repaired long ago can also reappear through fresh paint. In both cases the water meter and the boiler pressure stay steady, which is a quick way to tell them apart.
How do I know if the stain is from the bathroom above?
Run the shower for ten minutes and then the bath tap into the overflow while someone watches the ceiling. If the stain darkens or drips within an hour, the bathroom is the source. A stain that changes only after washing or bathing and dries out between times almost always comes from a seal, tray, waste or overflow above.
Is a dry ceiling stain still a problem?
If it feels dry, has a sharp edge and has not grown over a couple of weeks against a pencil mark, it is most likely the residue of a leak that was fixed. It can be sealed with stain block and painted. If it is soft, sagging or spreading, water is still arriving and the source needs tracing first.
What does a thermal camera show on a ceiling?
It shows temperature differences. Wet plasterboard reads cooler than dry because moisture evaporates from it, so a live stain appears as a cold patch that is often bigger than the visible mark. A leaking hot pipe appears as a warm line between the joists. This tells you quickly whether the water is still coming and where from.
Will insurance pay to find the leak behind a ceiling stain?
Most UK buildings policies include trace and access cover, which pays for locating the leak and opening up to reach it, though not for repairing the pipe itself. Gradual damage from a long-neglected leak may be excluded, so photograph the stain early and get the cause confirmed with a written report.
Find what is above the stain
If the loft is dry and the stain is still there, we can tell you in one visit whether it is the bathroom, a pipe in the void or nothing to worry about, with a thermal and moisture report your insurer can use.
