Thamesmead

What "system-built" means when something leaks

A 1960s or 70s system-built block was assembled from large precast concrete panels and floor planks, with the services designed in from the start rather than chased into masonry afterwards. That is genuinely different from every other building type in this list, and it cuts both ways.

In your favour: the pipework is not buried in the structure. It runs in vertical service ducts, usually a cupboard or a boxed shaft next to the bathroom and kitchen, with horizontal spurs into each flat. Someone designed the route, drew it, and expected it to be maintained. If the drawings survive, the search is short.

Against you: the structure itself is unforgiving. Precast concrete panels and hollow-core floor planks cannot be chased or notched without engineering advice, panel joints can carry water horizontally a long way, and the finishes are frequently a thin plaster skim directly on concrete with nowhere to hide a repair.

Open the duct first

The instinct on a leak is to find the wet plaster and start there. In these blocks that is backwards. The duct is where the pipework is, the duct is where the joints are, and the duct is where nine out of ten failures will be found, because nothing else about the installation is accessible enough to have been interfered with over sixty years.

What is in there, typically:

• Cold water down service or rising main, depending on whether the block has tanks.
• Hot water flow and return, if the block has a communal calorifier.
• Heating flow and return, if the block is on communal heating.
• The soil stack and waste branches.
• Isolating valves for each flat, which may or may not still turn.

Open it at the affected floor and at the floor above. That is often the whole job. It is also the step that requires permission, because the duct is almost always communal even where the cupboard door is inside your flat.

Communal heating: a leak that is nobody's flat

Many blocks of this era were built with communal heating from a central boiler house, and a good number still run it, sometimes modernised into a heat network with a unit in each flat. When the leak is on that system, several of the usual assumptions stop working.

• Your pressure gauge tells you nothing, because you do not have a sealed system of your own. The pressure is managed centrally.
• The symptom may be heat rather than water. Radiators not reaching temperature, or a persistently warm patch on a wall or floor where a buried flow pipe is losing.
• The make-up water is somebody else's bill. Which means a substantial leak can run for months without anyone having a financial reason to notice.
• Nobody in a flat can authorise the work. The system belongs to the landlord or the management organisation.

Where a flat is let, section 11 of the Landlord and Tenant Act 1985 implies an obligation on the landlord to keep in repair and proper working order the installations in the dwelling for space heating and heating water, and where the dwelling is part of a larger building that extends to parts of the building the landlord owns or controls which serve the dwelling. That is the provision most often relevant when a communal heating leak is being left unattended.

Our boiler pressure pages are written for sealed systems in individual homes, so treat them as background rather than as instructions if your heat comes from a central plant.

Concrete floors change which instrument works

The detection sequence in these blocks is not the one used in a Victorian house, because the materials behave differently.

Thermal imaging is the strongest tool here. A concrete floor plank or a panel wall has high thermal mass and conducts steadily, so a heating or hot water leak behind it produces a clear, stable thermal signature once the surface has had time to respond. It is slower than on plasterboard, and it rewards patience: image, wait, image again.

Acoustic is difficult. Concrete transmits sound extremely well and the blocks are noisy, with lifts, communal plant and a lot of transmitted living noise. A leak that sounds close may be two floors away.

Tracer gas is decisive on cold water. A cold supply leak inside a duct or behind a panel gives no thermal contrast at all. Draining the section and charging it with a hydrogen and nitrogen mixture is the technique that finds it, and it passes through concrete and screed to the surface where it is detected. That is what tracer gas detection is for.

Moisture mapping defines the spread, which matters here because water running along a panel joint can appear in a flat that does not adjoin the one it started in.

Asbestos, which in this stock is not hypothetical

Buildings constructed or refurbished before 2000 can contain asbestos, and its use in construction and refurbishment has been illegal only since 1999. A block built in the late 1960s sits squarely in the period when asbestos-containing materials were routine, and the places they turn up are precisely the places a leak investigation wants to go.

HSE list, among others: asbestos insulating board used for internal partition walls and bulkheads above ceilings, and for panelling, which is a common duct casing material; thermal insulation lagging around boilers, calorifiers and pipework; asbestos cement products including flues, downpipes and gutters; textured decorative coatings on ceilings and walls; and vinyl and thermoplastic floor tiles together with sheet and screed materials.

The practical position on a block of this age is that the landlord or managing organisation should hold an asbestos register, and it should be consulted before a duct panel comes off or a ceiling is opened. Any contractor who does not ask for it is a contractor to be wary of. We ask for it, and where it does not exist we will not open suspect material on spec.

Who you have to talk to before anything happens

This is the practical bottleneck. Ducts, risers, communal heating and the block's cold water services are not yours, whatever the cupboard door suggests. Work on them is instructed by the landlord, the housing association or the management organisation.

What to do in order: report it to them in writing with photographs and times; ask whether other flats in the same vertical line have reported anything, because that answer alone often locates the leak; ask for the asbestos register; and ask who holds the service drawings. Then, when an engineer attends, they can spend the visit finding the leak rather than finding out who to ask.

Where we are instructed on block work, we report in writing as standard, because the organisation instructing us will need the document more than you will.