Watch when the ceiling gets wet. Damp during the shower points to the tray, the silicone or the grout. Damp as the water drains or shortly after points to the waste and trap. Damp at random, even when nobody has showered, points to a pressurised supply pipe. Each one has a simple test you can run before anything is opened up.
The stain on the ceiling under the bathroom has come back. It dries to a faint brown ring over a few days, then somebody has a long shower and the patch darkens again, sometimes with a drip from the light fitting. You have looked at the shower and nothing is obviously wrong. The tray is intact, the silicone looks fine at a glance, and the bathroom floor is dry. So where is the water coming from, and how do you find out without taking the ceiling down?
The answer is usually in the timing. A shower has three separate systems that can leak, and each of them leaks at a different moment. Once you know which moment matches your stain, you can test that one system on its own.
Why the timing gives it away
Think of the shower as three things bolted together. The tray, tiles and silicone hold water in while you stand under it. The waste, trap and waste pipe carry it away once it has gone down the plughole. The hot and cold supply pipes feed the valve and are under pressure all day, whether the shower is running or not.
- Leaks while the shower is on come from the first group. Water is getting past the tray edge, the grout or a failed bead of silicone and running under the tray into the floor.
- Leaks as it drains and just after come from the second group. The waste fitting or the trap lets water out while it is flowing through, and nothing escapes once the pipe has emptied.
- Leaks at random come from the third group. A supply pipe or a fitting behind the wall is weeping under pressure, so the ceiling can be wet on a morning when nobody has been in the bathroom.
The complication is that water rarely drops straight down. It runs along the top of a joist, follows a pipe, soaks across a chipboard deck, and only drips through when it finds a low point or a gap. A stain in the middle of the kitchen ceiling can be fed by a shower waste in the far corner of the room above. The stain tells you there is a leak, not where it is. Our article on a ceiling stain when the loft is dry covers that travelling-water problem in more detail.
Leaks during the shower: tray, seal and grout
This is the most common of the three and the one most often missed, because everything can look sealed from inside the cubicle. Silicone has to bridge a joint between a tray and a wall that move at slightly different rates. Every time somebody steps in, the tray flexes a fraction, and over a few years the bead pulls away from one surface, leaving a hairline gap hidden under the mould-stained edge. Water running down the wall slips behind it and disappears under the tray.
Grout does the same once it starts to crack, and a run of tiles over the tray edge can pass a surprising amount of water. Cracked trays are rarer, though a thin acrylic tray fitted without full support underneath can develop a stress crack that hides in the textured surface.
How to test it
Block the waste with the plug or a cloth so nothing goes down the drain, then run water gently over the walls and the silicone with the hand-held head for a few minutes, keeping it away from the plughole. Let it stand on the tray for ten minutes before releasing it. If the ceiling darkens, the leak is in the enclosure. Wetting one wall at a time narrows it further. If the silicone has failed, cut the whole old bead out and let the joint dry for a day before resealing. A fresh bead over an old one traps water behind it and makes things worse.
Leaks after the shower: the waste and trap
Directly under the plughole sits the waste outlet, a rubber seal and a trap that connects to the waste pipe. It is out of sight once the tray is fitted, and it is the part most likely to have been assembled in a hurry. The seal perishes, the locking ring works loose, or the trap was cross-threaded from the day it went in. Because water only passes through it while the shower drains, this leak stops the moment the tray is empty, which is why the ceiling can be dry an hour later and wet again the next morning.
How to test it
Do the opposite of the tray test. Pour water straight into the plughole from a jug, keeping the tray and walls as dry as you can, for five minutes or so. If the ceiling responds, the waste is the culprit. Where there is a removable panel on a raised tray, watch the trap directly while somebody pours. Kitchen roll wrapped around the joints shows the first drop.
Leaks at random: the supply pipes
If the stain appears or grows on days when the shower has not been used, stop testing the tray. A compression joint behind the tiles, a pinhole in a copper pipe or a weeping connection on a concealed mixer valve is letting water out under pressure. This is the leak to take seriously, because it never switches off, and it is almost always hidden inside the wall or the floor.
How to test it
Two checks. First, with every tap and appliance in the house off, watch the water meter for a few minutes. If it moves, water is escaping on the cold side. Second, on a combi or sealed heating system, watch the boiler pressure gauge over a few days. A slow fall from its normal cold reading of about 1 to 1.5 bar, with no visible drip, points to a heating pipe passing through the bathroom floor. Either result means the leak needs locating rather than resealing, which is a job for our trace and access service.
| When the ceiling gets wet | Most likely cause | Your test |
|---|---|---|
| While somebody is showering | Silicone, grout, tray edge or a cracked tray | Block the waste, wet the walls and tray only |
| As it drains and shortly after | Waste fitting, seal or trap | Pour water straight down the plughole, keep the tray dry |
| Any time, including days with no shower | Supply pipe or concealed valve under pressure | Meter check with everything off; boiler pressure over a few days |
| Only after heavy rain | Not the shower: roof, flashing or a window above | Check the loft and the outside wall |
What a ceiling can take before it fails
Plasterboard copes with the occasional wetting and dries out with a stain. Repeated soaking is different. The board goes soft, the paper face bubbles, and if water pools above it the ceiling can sag. A bulge with water behind it is urgent, and we cover what to do in ceiling bulging with water. If there is a light fitting in the wet area, switch that circuit off at the consumer unit until it has been checked, and stop using the shower until you have found the source.
Cornish homes add a wrinkle. Many older cottages around Cornwall have first-floor bathrooms fitted into rooms that were never designed for them, with timber floors, lath and plaster ceilings and pipes threaded wherever they would go. A lime plaster ceiling absorbs a great deal of water before it shows anything, so by the time a stain appears the leak may have been running for weeks. In holiday lets the shower gets used far harder in August than in February, so a seal that copes in winter can let go in peak season.
Insurers, failed sealant and the report
Most UK buildings policies cover escape of water, the sudden or unforeseen release of water from a pipe, tank or appliance, and most include trace and access cover to pay for finding the leak and putting back whatever had to be disturbed to reach it. The limit is often in the £5,000 to £10,000 range, and it does not pay for repairing the failed pipe itself.
Failed silicone is treated differently by many insurers, because worn sealant and grout are usually classed as maintenance rather than an insured event. Whether the resulting damage is covered depends on the wording and on whether the insurer considers it gradual. That makes the cause matter a great deal. A report showing the water came from a failed waste seal or a pressurised joint, with moisture readings and photographs, supports a claim in a way that “the shower was leaking” does not. Read what trace and access insurance covers before you speak to your insurer, and photograph the ceiling from the first day.
How we find it without taking the ceiling down
When the home tests are inconclusive, or the leak is in the random category, a survey works through the suspects in order. We run the same isolation tests one system at a time, with a moisture meter on the ceiling and the floor around the tray so that a small change shows long before a visible drip. A thermal imaging camera picks up the cooler track that water leaves as it moves along a joist, which shows the route from the source to the stain. For a supply leak, acoustic equipment listens for water escaping under pressure and pins it to a short length of pipe, and tracer gas confirms it where the pipe can be drained.
Only once the source is confirmed does anything get opened, and then it is a small hole in the right place rather than a ceiling on the floor. That approach is the same whether the job is in Falmouth or on a farm above Bude. We offer leak detection for homes across Cornwall with a written report for the insurer as standard.
Frequently asked questions
Why does my ceiling only get wet after long showers?
A short shower may not put enough water past a failed seal or a slow waste leak to reach the ceiling. A longer one does, and the wet patch appears an hour or two later once the water has tracked through the floor. This pattern usually points to the enclosure or the waste rather than a supply pipe.
Can I just reseal the shower and see if it stops?
You can, as long as you cut out all the old silicone and let the joint dry first. If the ceiling stays dry afterwards, the seal was the cause. If it still gets wet, do not keep resealing. The leak is in the waste or a pipe, and the timing tests above will tell you which.
Is a shower leak covered by home insurance?
Damage from a leaking waste or pipe is usually covered under escape of water, and many policies include trace and access to find it. Failed sealant is often classed as maintenance, so the resulting damage may not be. Your policy wording decides, and a report that identifies the cause helps.
How long does it take for a shower leak to show on the ceiling?
It varies with how much water escapes and what it has to pass through. A drip onto a plasterboard ceiling can show within a day. A slow seep into a thick timber floor or a lime plaster ceiling can take weeks, by which point the joists and boards above have been wet for some time.
Do you need to cut the ceiling to find a shower leak?
Usually not. Isolation tests, moisture readings and thermal imaging locate the source from above and below without opening anything. If a small inspection hole is needed to confirm a waste or pipe joint, it is made at the confirmed point so that the repair and the making good stay small.
Stop the stain coming back
If the ceiling under your bathroom keeps getting wet, we can test the tray, the waste and the pipes in one visit and tell you exactly which is leaking, with a report your insurer can use.
