Underfloor leak detection finds the pipe leak hiding in the void below your floorboards before it reaches the ceiling of the flat below, using acoustic, thermal, and tracer-gas methods.
Most London housing stock built before 1939 (Victorian, Edwardian, and 1930s terraces) sits on suspended timber floors with a vented subfloor void underneath the ground floor. Hot, cold, and waste pipework runs through that void out of sight. When a pipe pinholes or a compression joint loosens, the water has somewhere to go that is not your floor finish.
The first signs are usually subtle: a damp spot on the bottom edge of a ground-floor skirting, a musty smell from the floorboards, a drop in mains pressure, or the water meter spinning with every tap and appliance closed. This survey finds the source without lifting every board in the house.
We start with a meter test at the stop tap to confirm a mains-side leak (any movement on a closed system means water is escaping). One or two floorboards are lifted at the most likely access point, normally near the kitchen or bathroom riser, to get a microphone into the void.
Acoustic listening uses Sewerin AquaPhon or SeCorr correlating loggers. These pick up the high-frequency hiss of pressurised water and localise to within a metre on copper. A FLIR thermal camera then sweeps the joists for cold trails on a cold-water leak, or warm trails on a hot-water or heating-side leak. Where the layout is unclear on the heating loop, we run a fluorescent UV dye trace through the suspect circuit and use a UV torch in the void.
Sometimes pipework runs under a concrete sub-base or sits inside an insulated screed slab (a 1990s or later refurb). There the acoustic signal stops carrying, and we escalate to the standard 5 per cent hydrogen and 95 per cent nitrogen tracer-gas test, read at the surface with a Sewerin Variotec. Lifted boards are always refitted with brass screws, not nails, so the next access is non-destructive.
Where this service applies
- Damp spot on a ground-floor skirting with no plumbing fixture above
- Musty smell rising from underfloor vents in Victorian and Edwardian terraces
- Mains water meter spinning with every tap and appliance closed (silent leak)
- Drop in mains pressure with no visible leak in the property
- Heating-loop pinholes on microbore under suspended timber floors
- Subfloor void wood-rot and airbrick condensation
- Insurance trace-and-access where the source is not visible from above
- Ceiling staining in the flat below from a suspected upper-flat leak
How we deliver
No surprises, no upselling. The exact path every job follows.
- 1
Meter test and pressure check
All taps, the boiler, and every appliance closed. Water meter watched for movement to confirm a mains-side leak. Mains pressure recorded at the stop tap. - 2
Symptom mapping and access point
Damp and musty zones marked on a quick floor plan, then the lowest-impact board to lift identified for void access, normally near the kitchen or bathroom riser. - 3
Acoustic localisation
Sewerin AquaPhon ground microphone or SeCorr correlating loggers across the void, picking up the hiss of pressurised water. Localises to within a metre on copper. - 4
Thermal sweep of joists
FLIR camera over joists and the underside of the floor finish. Cold trails for cold-water leaks, warm trails for hot-water and heating-side leaks. - 5
Dye trace where layout is unclear
Fluorescent UV dye introduced into the suspect supply or heating circuit, UV torch used in the void to find the exit point on confused pipe runs. - 6
Tracer gas escalation
Where the run is under concrete sub-base or insulated screed and acoustic does not carry, the line is depressurised and charged with 5 per cent H2 and 95 per cent N2, read at the surface with a Sewerin Variotec. - 7
Reinstatement and report
Lifted boards relaid with brass screws (not nails) so the next access is non-destructive. Written report with leak location, photographs, and a separate repair quote.