Water Leak Under the Floor? How We Find It

Houses around Watford and across London have two kinds of floor, and a leak behaves differently under each. Victorian and Edwardian terraces and most 1930s semis have suspended timber floors at ground level, with a void beneath and pipes clipped to the joists. A leak there drips into the void, soaks the ground or the joist ends, and often shows only as a musty smell or a springy board. Later houses and extensions have solid concrete floors with pipes laid in the screed. Water from a leak in a screed spreads sideways under the finish and appears wherever it finds a way up.

The first mistake people make is to open the floor where the damp is. Water travels along joists, over the damp proof membrane and through the screed, so the wet patch is often a metre or more from the pipe. Lifting boards at random, or chasing out tiles until the leak appears, destroys a floor finish that may be hard to match. Before anything comes up we find out which system is leaking. The meter test with everything off points to the cold mains. A boiler that keeps losing pressure points to the heating. A test strip on any water we can reach tells the two apart.

Each method does something different through the floor finish. The thermal imaging camera reads through laminate, carpet and tiles to show a warm heating pipe and the cooler patch where water has soaked the floor. The acoustic ground microphone sits on the surface and listens through boards, tiles and concrete for the noise of a pressurised mains leak. Where a pipe is silent or plastic, we drain it and fill it with a hydrogen and nitrogen tracer gas. The detector then samples along board joints, skirting boards and grout lines until it finds where the gas is surfacing. A borescope through a small hole lets us look into the void.

That combination is why only one board or one tile normally comes up. The leak is located to a small area, marked on the floor, photographed and recorded in a written report with the readings and thermal images. If you want the repair done on the same visit we open the marked point by hand, repair in copper or barrier pipe, and leave the opening ready to make good. Most buildings insurance policies include trace and access cover, which pays for finding the leak and making good the floor. If a leak cannot be located without opening the floor, we say so and explain the options.