Hidden Leak Under the Floor in SE London

Last updated 19 September 2026.

How a leak under the floor is traced without opening it up

It's one of the harder leaks to live with, because the natural response is to lift a board and look, and that's exactly the wrong first move. Suspended timber floors, chipboard decks and even solid concrete slabs across SE London's older and post-war housing hide a leak well: water spreads sideways under a slab, or runs along a joist to the lowest point in the room, so the spot where you can see or feel a problem is rarely where the pipe has actually failed. Lift the wrong board and you've opened up flooring for nothing.

Tracer gas. A safe tracer gas is put into the empty pipe and followed with a sensitive detector to the point it escapes. It's the right tool where a pipe runs under a solid concrete floor, and for small, slow, pressurised leaks that don't put out enough water to trace by sound or sight alone.

Dye testing. A coloured dye is added to the water at a shower, bath or waste and traced to wherever it comes through the floor below. It's the fastest way to confirm or rule out a bathroom waste pipe as the source when the room above has one.

Thermal imaging. Water changes the surface temperature of the floor and any covering above it. A thermal camera picks up that temperature difference, which is how a "warm patch" on the floor is very often confirmed as a wet patch underneath rather than an underfloor heating pipe fault.

Acoustic listening. A pipe leaking under pressure makes a sound that travels through the floor structure. We use acoustic listening equipment on the surface to trace that sound back along the run, particularly effective on mains and other pressurised supply pipes.

Moisture mapping. Calibrated moisture meter readings are taken across the floor surface and up the skirting at the edges of the room. Plotted together, those readings show which direction the water is spreading from, which is what confirms exactly where the leak sits before any board comes up.

Used together, these findings usually agree on the same small area, and that's the only place that gets opened, if it needs to be opened at all.

What the visit looks like

A surveyor comes to the property, asks what's been noticed and since when, and works the affected room with acoustic and thermal equipment plus a moisture meter. Most visits are completed in a single appointment. You're shown what's been found there and then, with thermal images and moisture readings kept as a written record, not just a verbal opinion about which board to lift.

What you get

By the end of the visit the leak is located and documented: where it is, how far it has spread, and what needs to happen next. If a plumber's repair is needed we'll say so plainly. If water has already soaked into the floor structure or the room below, drying will need to be part of the plan, because mould can start to take hold within 24 to 48 hours of water getting into timber or plaster. Finding the leak early is what keeps a plumbing job from turning into a much bigger drying and remediation job.

Price: Leak detection is a fixed £650.

Why this is common in SE London

Across south east London's boroughs, suspended timber ground floors are the default in Victorian and Edwardian terraces, and many of those houses now sit above unseen voids and old cellars that have never been touched since they were built. Post-war and ex-local authority low-rise blocks more commonly have solid concrete ground floors, where a leak spreads sideways under the slab instead of pooling straight down, so the wet or warm patch you notice can be some distance from the pipe that's actually failing. Loft and basement conversions, popular across the area's Victorian stock, add extra pipe runs boxed in under new flooring with no access left to check them. In all three cases the same rule applies: what you can see on top of the floor is a clue, not the answer, and tracing the sound and the temperature is what turns that clue into an exact location.

Who we are

Damp & Mould Solutions UK is a leak, damp and mould solutions company covering leak detection, damp investigation, mould inspection, mould remediation and structural drying across south east London. We're rated 5.0 on Google from 20 reviews. The company is registered with Companies House (company number 16687136), registered office 19 Ravenscroft Crescent, Eltham SE9 4LL.

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