What should you do about a water leak under your floor or house?

Turn off the water at the stopcock, isolate electrics if water is near them, and get a plumber or leak-detection specialist to find and stop the leak. Report it to your insurer promptly, as hidden under-floor leaks can be covered, and check whether your policy includes trace and access cover for the cost of locating the leak. Document everything and avoid pulling up floors yourself before the insurer has advised on the process.

Leaks under a floor or beneath the property are tricky because the water is out of sight and can cause a lot of damage before you notice it, showing up as a warm patch of floor, an unexplained rise in your water bill, the sound of running water, or damp and musty smells. If you suspect one, turn off the mains stopcock and, if there is any chance water has reached wiring, isolate the electrics and keep clear.

Locating a hidden leak is a job for a professional with non-destructive leak detection, not guesswork that means ripping up floors. This matters for your claim because many policies include trace and access cover, which pays the cost of finding and getting to the leak, for instance lifting flooring, as well as putting it back afterwards. Check whether you have this cover before work starts.

Report the situation to your insurer promptly. Damage from an escape of water, meaning water escaping unexpectedly from pipes or fittings, is commonly covered even when the leak was hidden, provided it is sudden rather than the result of long-term neglect. Do not assume you are uncovered because the leak was slow to reveal itself; the sensible reading of most policies is that you claim promptly once you discover it.

Keep strong evidence, because under-floor claims are often questioned on cause. Get the plumber's or leak-detection report in writing, stating what failed and where, and take photos of the damage and the exposed pipe once it is found. Keep receipts for detection, drying and repair. This documentation is what separates an accepted hidden-leak claim from a disputed one.

Watch out for two things insurers scrutinise: whether the leak was gradual wear and tear, which is usually excluded, and whether the resulting damp or rot built up over a long period. Neither defeats a claim for the sudden escape on its own, but both are common reasons for a low offer or refusal, so professional evidence on cause is worth having. If your cover is unclear, check your policy wording or get the claim reviewed.

How leak detection works

Non-destructive detection means finding the leak before opening anything up. Specialists combine several techniques rather than relying on one.

Thermal imaging: shows temperature differences through a floor or wall, effective on heating and hot water pipes.
Acoustic detection: amplifies the sound of water escaping under pressure, used to pinpoint a spot along a run.
Tracer gas: a harmless gas is put into the isolated pipe and detected where it surfaces, which works well on cold pipes that thermal imaging cannot see.
Moisture mapping: readings taken in a grid to show where water has spread and where it is most concentrated.
Drain cameras: used where the source may be waste pipe or drainage rather than supply.
Pressure testing: isolates sections of pipework to confirm which one is losing water.

Underfloor heating leaks

A leak in an underfloor heating circuit is a particular problem because the pipework is buried in screed under the finished floor, and the damage announces itself as a heating system that keeps losing pressure rather than as visible water.

Detection usually relies on thermal imaging while the system runs, and repair means breaking out a section of screed. Where the pipe is a continuous loop, the practical choice is sometimes between repairing one joint or abandoning that circuit. Because the cost of getting to the pipe dwarfs the cost of the repair, trace and access cover matters more here than almost anywhere else in a home.

Who pays for finding the leak

Detection is usually charged separately from repair, and a survey commonly runs into the hundreds of pounds before anyone lifts a floorboard.

Trace and access cover is what pays it, along with the cost of the opening up and the making good afterwards. It is normally capped, often somewhere around £5,000, and the cap applies to the finding and reinstating rather than to the water damage itself. Check the limit in your schedule before instructing anyone.

Ask the insurer to approve the detection company first if you can, because a firm instructed without agreement is sometimes refused later. If the leak is on the supply pipe outside the house, your water company may investigate at no charge, so it is worth a call before you commission a private survey.

Drying a solid floor takes months

Once the leak is fixed, a suspended timber floor can be dried in a few weeks with the boards up. A solid floor is a different proposition, and it is where under-floor claims tend to overrun.

Water gets into the screed and the concrete slab beneath, and both release it slowly. Drying often needs the floor covering removed and specialist equipment, and it can run for a couple of months on a badly saturated slab. Insulation beneath a floating floor holds water even longer and sometimes has to come out rather than be dried.

Do not let a new floor go down on a reading somebody took at the surface. Ask for readings taken at depth and for the drying certificate before reinstatement is agreed. A floor laid on a damp slab lifts, cups or smells within a year, and by then the claim is closed and the argument is about who pays to do it twice.