The building was never meant to have sixty bathrooms in it
Start with what the original building was. A 1960s or 1980s office block has a structural frame, a central core with lifts, stairs and a small cluster of toilets, and large open floor plates served by a suspended ceiling and often a raised access floor. Water went to the core and nowhere else.
Converting that into flats means putting a kitchen and a bathroom into every unit, which is somewhere between twenty and sixty new wet rooms in a building that had four. All of that pipework is an addition, and it had to find a route through a structure with no provision for it.
That single fact explains the failure pattern in these buildings, which is different from a purpose-built block in three specific ways: the runs are longer, the junctions are more numerous, and the routes are shared between flats in ways the residents cannot see.
Where the pipework actually went
Above the suspended ceiling
The most common answer. Horizontal supply and waste runs sit in the ceiling void of the floor below the flat they serve. The consequence is immediate and unhelpful: a leak in your ceiling is very often pipework serving the flat above, running over your head rather than through their floor. Access to repair it is from your side, which makes for interesting conversations about who instructs.
In the raised access floor
Where the office had a raised floor for cabling, many conversions kept it and used the void for services. This is the good outcome. A raised floor is designed to be lifted, tile by tile, without damage. If your flat has one, say so when you book, because it changes the job from invasive to trivial.
In new boxing and stud walls
Vertical drops and connections to fittings run in studwork built during the conversion. Usually plasterboard, usually with no access panel, usually finished before anyone thought about maintenance.
New risers punched through the slab
New vertical service routes had to be created, often by core-drilling the existing floor slabs. Those penetrations are fire-stopped and sealed, and they are also the exact route water takes between floors when something above fails.
One leak, a whole floor of flats
Because the horizontal distribution sits in a shared ceiling void that crosses flat boundaries, a single failure in these buildings affects more properties than it would in a purpose-built block. Water enters the void, runs along the top of the slab or along a cable tray, and drops through the first convenient penetration, which may be two or three flats away from where it started.
What follows from that:
- The flat with the damage is frequently not adjacent to the flat with the fault.
- Locating the leak requires access to ceiling voids in flats that are not yours and are not damaged, whose occupiers have no motivation to help.
- The managing agent has to coordinate it. A leaseholder cannot.
- Where a flat is let, the landlord's repairing obligation under section 11 of the Landlord and Tenant Act 1985 covers installations for the supply of water and for sanitation and, where the dwelling forms part of a larger building, extends to parts of that building the landlord owns or controls which serve the dwelling.
The practical advice: report in writing to the managing agent on day one, and ask them specifically whether any other flat on your floor or the floor above has reported water. That question resolves a meaningful proportion of these jobs before anyone attends.