The single most expensive assumption in a tower
The stain is on your ceiling, so the leak is in the flat above. That assumption gets a door knocked on, a relationship strained, a floor lifted, and nothing found, perhaps two or three times, before anyone widens the search.
Here is why it is wrong so often. A post-tensioned or reinforced concrete slab is watertight. Water escaping above it cannot go down through it, so it spreads horizontally across the top of the slab under the floor build-up until it reaches something that does penetrate: a soil pipe boss, a riser duct, a lighting recess, a sprinkler drop, a cable penetration, a movement joint. Then it goes down. The distance between the failure and the penetration can be the full width of an apartment, and the penetration can serve a completely different flat from the one above yours.
Two or three floors of vertical travel is unremarkable in a tower, because once water is inside a riser or a dry service shaft it keeps going until something stops it. We have opened ceilings on the tenth floor for water that entered on the fourteenth.
Four candidates, and how to tell them apart
| Source | What gives it away |
|---|
| Pressurised cold or hot riser in the shaft | Continuous, unrelated to anyone's usage pattern, often worse at times of low demand when pressure is highest. Affects the same vertical line on multiple floors. |
| Sprinkler or wet riser pipework | Also continuous, but the water is often discoloured and the system will usually register a pressure alarm. Not a plumber's job. |
| Comfort cooling condensate | Seasonal. Appears in hot weather, stops in winter, small volumes, clean water, usually near an FCU or a ceiling void run. Very commonly misdiagnosed as plumbing. |
| Inside one apartment | Follows use. Nothing overnight, worse after showers or a dishwasher cycle. Confined to one area rather than one vertical line. |
Establishing which of these it is can often be done before anything is opened, purely by logging when the water appears against what the building is doing. If nobody has kept that log, start one. Three days of it is worth more than an hour of guessing.
Arrange the access before the appointment
This is the difference between a two-hour job and three wasted visits, and in a managed tower it is not something an engineer can sort out at the door.
- Estate management approval. Most towers require contractors to be inducted, to provide method statements and risk assessments, and to book a lift slot. Same-day attendance is often simply not permitted.
- Riser cupboard access on every floor in the affected line, not just yours and the one above. This is the step most often skipped and it is the one that resolves the job.
- Isolation authority. Who can shut a riser down, and what notice do residents need? In some buildings that is a scheduled event rather than a decision.
- Permits. Hot works, and in some buildings any work in a shaft, require a permit issued in advance.
- Drawings. Someone has them: the managing agent, the building manager, or the developer. Service drawings turn a search into a check.
Where communal pipework is involved, the instruction has to come from the party responsible for it. Where a flat is let, the landlord's repairing obligation under section 11 of the Landlord and Tenant Act 1985 extends to installations for the supply of water and sanitation and, where the dwelling is part of a larger building, to parts of that building the landlord owns or controls which serve the dwelling.
Why the usual techniques behave differently in a tower
Acoustic listening struggles. A concrete frame is an excellent sound conductor and a tower is full of mechanical plant. Pump noise, lift machinery, ventilation and the building's own structural transmission mean a leak can be heard clearly on three floors at once, which tells you almost nothing about where it is.
Thermal imaging is good but needs a differential. It reads hot water and heating pipework well through plasterboard and screed. A cold water leak in a shaft at ambient temperature gives you very little.
Tracer gas is the workhorse. A drained section charged with hydrogen and nitrogen and surveyed at the surface will find a cold water loss inside a riser or under a floor build-up when nothing else will, and it does not require the building to be taken apart to try.
Moisture mapping defines the edge. In a tower it is mostly used to establish how far the water has spread within the floor build-up, which matters enormously for drying and for the insurance claim, and rather less for locating the source.
What to do in the first hour
- Ring the building manager or concierge, not just your neighbour. They can see whether anyone else has reported water in the same line.
- Turn off electrics to affected rooms if water is near a light fitting or a socket.
- Do not pierce a bulging ceiling unless you have somewhere for the water to go and the power is off.
- Photograph everything with timestamps, and note the time the water appears and stops.
- Report it in writing to the managing agent, because the block buildings policy claim starts from that notification.
If it is coming through the ceiling right now, water coming through a ceiling covers the immediate steps in more detail, and ceiling leak repair covers what we do about it afterwards.
What is not ours
Sprinkler and wet riser systems are maintained under a separate regime by specialist contractors and we do not touch them. Comfort cooling condensate is a mechanical services job, though we will identify it for you rather than chase it as a plumbing leak. And where the water is coming through the facade in wind-driven rain rather than from pipework, that is a building envelope problem for the managing agent's facade contractor. We would rather say so in the first half hour than bill you for confirming it.
