Leak Detection Under Floorboards in London
A leak under floorboards is located from above first, with moisture readings, acoustic listening and a pressure test, so that only one board needs lifting to confirm it. The fixed-price package is £580, known before the visit. No VAT is charged.
What the visit covers
- Moisture readings across the boards, skirting and nearby walls to draw the wet area
- A pressure test on the supply and heating circuits to say whether a pipe is losing water
- Acoustic listening and thermal imaging where the pipe type and the floor allow it
- Lifting a single board at the strongest reading, with an endoscope through the gap where one is needed
- A written report of what was found and where, with photographs of the opened bay
Published prices
What it costs
- Fixed-price leak location package
- The package gives one fixed price, known before the visit, to locate a leak in one property using whichever methods the leak needs.
- £580Fixed price
Or by the hour
- Standard leak detection
- General water leak detection in a property.
- £180an hour
- Trace and access
- Tracing a leak that is inside a structure.
- £180an hour
No VAT is charged
A fixed hourly rate that cannot rise on the day
No find, no fee applies when a live leak inside your own property cannot be located. No find, no fee in full
Order of work
Map the floor from above
Moisture readings are taken in a grid, then compared with the walls and the room below. Water often runs along a joist before it shows, so the wettest board is a clue and not yet the answer.
Decide which pipe
A pressure test separates the supply, the heating circuit and the waste. If the gauge holds on every circuit, the water is not coming from a pressurised pipe and the search turns to waste, drains or the outside of the building.
Open one bay
One board is lifted at the best candidate position. A borescope goes along the joist space so the pipe can be seen before any further boards are touched. See trace and access surveys for how the opening is chosen.
What is different about a floor with a void under it
Many London homes built before the mid twentieth century have suspended timber floors: boards nailed to joists, with an air space below. The pipes run in that space, often notched through the joists. Nothing is buried, so a leak there can be reached by lifting one board.
That is the opportunity and the difficulty. The space lets water travel sideways along the joists and drip a long way from the fault, so the damp patch, the swollen skirting and the warped board can all be metres from the pipe. Lifting boards at the wettest spot is therefore a poor first move. It opens the floor where the water arrived, not where it started.
Solid concrete floors need a different approach, because the pipe cannot be reached with a board. That case is covered in the guide to a leak in a concrete floor.
How the leak is located before anything is lifted
The visit starts with readings that do not damage the floor. A moisture meter on the boards gives a map of where the timber is wet, and a thermal imaging camera can show a cool or warm trace of water on the surface when the pipe is hot or the floor is thin. Readings from a pin meter are only a guide, and they are less reliable on very wet timber, so the map is checked against what is happening in the room below.
A pressure test then answers the question that matters most: is a pipe under pressure losing water? The method is explained in how pressure testing finds a leak. A gauge that falls points to a leak, and which circuit was isolated points to the pipe run. A gauge that holds is just as useful, because it rules out the supply and heating circuits and tells you not to open the floor for them.
Where the pipe is metal and under pressure, acoustic detection can hear the leak through the boards. Plastic pipe carries sound poorly, and a leak at a loose compression joint can be silent, so listening is one input and not the verdict.
| Reading | What it suggests | What it cannot tell you |
|---|---|---|
| Wet boards in one patch, gauge falls | A pressurised pipe is leaking within reach of that area | Which side of the joists the pipe runs on |
| Wet boards, gauge holds | Waste, overflow, rain or condensation more likely than a supply pipe | Which of those it is without more checks |
| Dry boards, gauge falls | The pipe is losing water somewhere else, possibly in a wall or the void edge | The location |
| Quiet pipe, wet boards | A joint weeping slowly, or a plastic pipe that carries sound badly | That nothing is wrong |
Lifting the board: what is opened and what is not
Once the readings agree on a zone, one board is lifted at the best position. Square-edge boards can often be lifted whole. Tongue-and-groove boards usually need to be cut free along a joist, which leaves a neat edge that a carpenter can refix. The opening is kept as small as the view allows, and a borescope or endoscope is passed along the bay so that the pipe can be seen without clearing a whole room.
The visit ends with the leak located and photographed. A small repair, such as tightening a fitting or replacing a small part on the pipe, can be done on the same visit once the leak is found, agreed first. A larger repair is quoted before any work starts, and the leak is stopped in the meantime. Refixing the board and drying the void are separate jobs; see drying out a property after a leak. The report records the position and the photographs so that whoever does the repair can go straight to the spot. See leak repair after detection.
Cables and pipes sit just under the boards. Lifting them blind risks nailing or cutting into one, so the opening is left to the person doing the survey.
What it costs, and when nothing is found
Inside one property, the £580 leak detection package locates the leak before anyone lifts a board, at a price known before the visit. Tracer gas is included by default. The package excludes larger repairs, making good and leaks outside the property. No VAT is charged. See what the package includes for the full scope, and hourly rate versus package for how to choose.
If a job is better suited to hourly work, the rates are £180 an hour for standard detection and £180 an hour for trace and access, each no VAT is charged and a fixed hourly rate that cannot rise on the day.
No find, no fee applies when a live leak inside your own property cannot be located. The no find, no fee page sets out both limits. A leak that belongs to a neighbour, a communal pipe or the water main is a located leak and is charged, and a survey that shows no leak exists is charged too, because ruling a leak out is the answer.
Some home policies include trace and access cover for a hidden leak under a floor. Cover depends on the policy and the insurer decides; see insurance-covered leak detection.
Limits of the method
A fitted carpet over foam underlay, a laminate floor laid over the boards, or a floor with a thick layer of insulation under it all weaken thermal and acoustic readings. In those cases more of the answer comes from the pressure test and from a small, planned opening.
A leak that runs only when a tap or appliance is in use may not show on a standing pressure test. The test is then repeated with the suspect fitting running, which takes longer. Nothing replaces the pipe being seen, which is why the visit finishes with a lifted board and a photograph. Clearing furniture and finding the stop tap beforehand shortens the visit, as how to prepare for a leak detection visit explains, and how long a leak detection survey takes covers what sets its length.
Sources
Decay threshold for timber: Building Conservation, Timber Decay article, on decay ceasing when timber moisture content falls below about 20 per cent (consulted October 2026).
Moisture meter limits: Forest Products Laboratory, Wood Handbook, chapter 13, citing ASTM D4444 on electrical moisture meters being generally limited to readings below about 30 per cent, the fibre saturation point (consulted October 2026).
Questions customers ask
Do floorboards have to be taken up to find a leak?
Usually one board, not the room. Moisture readings and a pressure test narrow the area first, and one board is lifted where the evidence points. A borescope along the joist space shows the pipe without clearing more floor.
Can a leak under floorboards be found with a thermal camera alone?
Sometimes, if the pipe is hot and the floor covering is thin. A cold pipe, a carpet over underlay or insulation under the boards can hide the pattern, so the camera is checked against a pressure test and moisture readings.
How long can water sit under floorboards before it causes damage?
It depends on how long the timber stays wet. Timber stays sound while it is dry. Decay fungi need timber that stays damp, typically above about 20 per cent moisture, so a leak that is fixed and allowed to dry is a very different risk from one that runs for months. See the sources below.
Is the leak always under the damp patch?
No. Water follows the joists and the gaps in the floor, so the wettest board can be some distance from the pipe. That is why the search starts with readings across the whole floor and a pressure test.
How much does it cost to find a leak under floorboards?
The fixed-price package is £580 to locate a leak in one property, and no VAT is charged. Hourly work is £180 an hour for standard detection, no VAT is charged, and a fixed hourly rate that cannot rise on the day. Larger repairs and making good the floor are not included.
What if the leak is under a laminate or engineered floor?
Those floors float over an underlay and are harder to lift in one place. The pressure test and moisture map still apply, and the opening is planned with the least damage to the floor in mind. The warped floor guide explains what that damage tells you.