Water leak under the floor of a London flat: who is responsible

A water leak under the floor of a London flat almost never shows in the flat it comes from. It shows in the ceiling of the flat below, and the first you hear of it is a knock on the door from a neighbour or an email from the managing agent. Nobody knows whose pipe it is, and everybody wants someone else to pay.

This page covers leaseholders, freeholders and the flat below: who is responsible for which pipe, what the lease and the building's insurance normally say, and how a leak under a floor is traced to a point without lifting the whole thing. It applies to the part of London we cover, the N, E, EN, IG and RM postcodes north and east of the river.

Why the leak is in one flat and the damage in another

Water runs down. A pipe under a kitchen or bathroom floor on the second floor drips into the void between that floor and the ceiling below, soaks the joists or the slab, and comes out as a stain, a bulge or a drip in the flat underneath. In the Victorian conversions across Hackney, Haringey and Islington the floor void is timber and the water can travel a long way sideways before it shows.

In the newer blocks around Canary Wharf, Stratford and the Lea Valley the floors are concrete and the pipes run in ducts and risers. A leak there tends to track along the duct and appear two or three flats down, or in the corridor. Either way, the flat with the stain is rarely the flat with the leak.

Who is responsible: the lease decides

The lease sets out what is demised to you, meaning what you own and must maintain, and what is retained by the freeholder. In most London flats the pipes that serve only your flat are yours, from the point they branch off a shared pipe. Shared pipes, risers, the communal supply and the structure between flats are the freeholder's, maintained through the service charge.

That means a leak on the pipe under your own bathroom floor is your responsibility, even though the damage is downstairs. A leak on a riser in the duct, or on the communal mains before it splits, is the freeholder's or the management company's. The supply up to the building's boundary belongs to the water company: Thames Water for most of this part of London, Affinity Water in parts of the EN postcodes.

Rented flats add a layer. The tenant reports it, the landlord of the flat it comes from is responsible for the repair, and the leaseholder below claims for their damage. The managing agent will usually want a report that settles which flat and which pipe before anyone instructs a plumber.

• Pipes serving only your flat: the leaseholder
• Risers, shared pipes and the structure: the freeholder, via the service charge
• The supply to the building boundary: Thames Water
• Damage in the flat below: usually their own insurer first, then recovery
• Rented flat: the landlord, not the tenant

Insurance in a block of flats

Most blocks have a single buildings policy taken out by the freeholder or management company, and every leaseholder pays a share. That policy normally includes escape of water, and often trace and access, which covers the cost of finding the leak and reinstating what was opened to reach it. There is usually an excess, and the lease says who pays it.

Your own contents policy covers your belongings and nothing of the structure. If the leak is from your flat and the damage is downstairs, the neighbour's loss usually goes through the block policy, with the excess passed to whoever was responsible under the lease. Ask the managing agent for the policy name and the claims line before the visit, because insurers want to be told early.

How the leak is traced without lifting the floor

Charlie starts in the flat with the damage and works up. A moisture meter and the thermal camera on the stained ceiling show the extent of the wet area and the direction the water is travelling from. That usually points at one room in the flat above, sometimes two flats up.

In the suspect flat each system is isolated in turn. The cold supply is shut at the flat's stop tap and a gauge fitted; a drop means a supply leak. The heating is pressure tested; a drop means a heating pipe. If both hold, the fittings are run one at a time, shower, bath, basin, toilet, while the ceiling below is watched. That catches waste pipes and seals, which no pressure test will.

Once the system is known, the pipe is pinpointed. The thermal camera shows a hot water or heating pipe through tiles and laminate, and the bloom of water around the break. Tracer gas, pumped into a drained heating or supply pipe, is followed with a detector to the exact spot. Acoustic listening picks up a pressurised supply leak under a screed floor.

The outcome is one marked spot on the floor, which the plumber opens, rather than a kitchen or bathroom stripped out to look. The report with photographs and thermal images goes to the leaseholder, the freeholder and the insurer. No find, no fee applies.

The flats we see most in north and east London

Victorian and Edwardian terraces split into two or three flats are the bulk of the work in Dalston, De Beauvoir, Harringay and around Arsenal. The pipework has been added to by every conversion and the floors are timber, so the leak is often a waste pipe or a heating pipe from a boiler in a cupboard.

The purpose built blocks on the Isle of Dogs, at Canary Wharf and around Bow and Canning Town have concrete floors, underfloor heating in the newer ones, and a lot of pipework in boxed ducts. The leak is more often a push fit joint behind a bath panel or a connection in a riser cupboard.

Out through Loughton, Buckhurst Hill, Cheshunt and Hoddesdon the blocks are smaller, 1960s to 1980s, with the supply coming up through a ground floor slab and the heating pipes in the screed. Charlie has found leaks in Dalston, De Beauvoir, Harringay, Canary Wharf, Loughton and Cheshunt, and the same method works in all of them.

What to do before anyone visits

If the drip is active, catch it, and if a ceiling is bulging pierce it over a bucket so the water comes out before the plasterboard does. Photograph the damage with the date, and ask the managing agent for the lease plan and the block insurance details.

Knock on the door above and ask them to check the meter and the boiler pressure with everything off. If they will not engage, the managing agent can usually require access under the lease. Then ring 07897 020 680. We cover the N, E, EN, IG and RM postcodes from Haverhill, about 55 miles away, and can usually book you in within 24 to 48 hours.

Questions people ask