Most plumbing advice assumes your pipes are yours. In a mansion block, a good proportion of them are not. The water arrives in your flat through pipework that runs vertically through the building, serves your neighbours as well as you, and belongs — in most leases — to the freeholder. That single fact explains a great deal of what frustrates people about plumbing in this stock: why a problem in your bathroom cannot be fixed in your bathroom, why nobody can turn a valve off at midnight, and why the answer to "can you just move the soil pipe" is usually no.
This page explains how these systems are actually arranged, where responsibility tends to sit, and how to plan work in a flat that hangs off a shared riser without discovering the constraints halfway through.
What a riser actually is
A riser is a vertical route through the building carrying services. In the Edwardian and interwar block stock that fills Maida Vale, St John's Wood and much of Marylebone, you will usually find some combination of:
- a cold water rising main, or a distribution pipe fed by a tank in the roof
- a soil stack taking WC discharge down to the drain
- a waste stack taking baths, basins and sinks
- a vent, often the soil stack extended up above the roof
- in some blocks, communal heating and hot water flow and return
These usually sit in a duct — a boxed vertical shaft, frequently in a corner of a bathroom or kitchen, sometimes in a communal cupboard on the landing, sometimes in the space between two flats. Each flat is teed off. Which is precisely the problem: your bathroom is one branch of a system that runs from the roof to the basement through everybody's home.
The arrangement varies more than you would expect. Blocks built as flats tend to have properly designed risers, often with reasonable access. Houses converted into flats — the majority of the stock in Bayswater and much of Fitzrovia — often have no true riser at all. Instead they have a soil pipe on the back elevation, waste running out through the wall wherever it was convenient, and supply threaded up through cupboards and voids in whatever sequence the various conversions produced. In that stock, the pipe in your floor may genuinely serve your neighbour, and nobody has a drawing.
The demise boundary — the thing that decides everything
Almost every argument about riser plumbing reduces to one question: where does your demise end and the common parts begin?
The broad general position in many flat leases is that pipework serving only your flat, within your flat, is your responsibility, and pipework serving more than one flat is part of the common parts and the freeholder's responsibility. So the branch from the riser to your basin is usually yours; the riser itself is usually not.
But that is a generalisation and it will not survive contact with a specific lease. Some leases draw the line at the face of the duct. Some at the first joint. Some are silent on pipework in structural floors — which is exactly where the awkward failures happen. Some define common parts in a way that leaves an unhelpful gap. And in converted houses where a pipe serves two flats but was never intended to, the general rule barely applies at all.
So the honest advice is simple: read your lease, and if it is not clear, ask your managing agent to confirm in writing before you commit to anything. This is not lawyerly caution. It decides who pays for a burst — see our guide to a burst pipe in a mansion block — and whether you can lawfully touch a pipe at all.
Isolation, and why you probably cannot do it
Your flat stopcock closes your flat. It does nothing to the riser.
Riser isolation is usually a valve serving that riser for a floor, several floors, or the whole stack. Closing it affects every flat on it. That is why it sits with the porter or the managing agent's contractor, often behind a locked door, and why leaseholders should not go looking for it with a wrench. It is also why the honest answer during a live leak on a communal pipe is: call the porter, not a plumber, first.
What is worth doing now, in advance: ask whether the block has riser isolation, where it is, who holds the key, and what the out-of-hours arrangement is. In practice some blocks have well-marked valves and good records. Some have valves that have not been turned since the war and will not close. Some have no discrete isolation at all, meaning the whole block has to come off to fix one branch. Knowing which of those you live in is genuinely useful information, and the time to find out is not while water is coming through a ceiling. Our guide to an emergency plumber in Central London covers the same point from the emergency side.
Access hatches, or the lack of them
Here is the recurring practical problem with these blocks. The riser is in a duct. The duct was accessible when the building was new. Then, over ninety years, successive bathroom refits tiled over it, built vanity units against it, and boxed it in permanently. Now the valve serving your flat's branch is behind sixty tiles and a stud wall.
The consequences are real. A ten-minute repair becomes a day because of what has to come off and go back. In listed stock, or where the finish is stone or a discontinued tile, what comes off may not go back at all. And when the managing agent needs access to the riser for the building's benefit, they generally have rights of access under the lease — and if your bathroom is in the way, the making-good conversation is one you would rather have had before you tiled over it.
So: if you are opening a duct for any reason, put a proper access hatch back. If you are planning a bathroom refurbishment, specify hatches at every valve, every rodding eye and every connection in the duct, and choose a tile or panel arrangement that can be lifted. This is the cheapest decision in the whole job and the one people most often skip because it interrupts a clean tiled face. Our tiling page covers how to detail a hatch so it does not look like an afterthought.
What goes wrong on shared risers
Blockages in the soil stack. Everybody's wipes, one pipe. The consequences land at the bottom, which is why lower-ground and ground-floor flats suffer for the building's habits. Covered in more detail in our guide to a blocked toilet in a London flat.
Corrosion and scale. Old cast iron soil stacks corrode. Old galvanised or steel distribution pipe closes up internally. The building's flow declines over decades and the top floor notices first — see low water pressure in a London flat.
Venting problems. If a stack's vent is blocked or has been altered, you get gurgling wastes, traps being siphoned dry, and drain smells appearing in flats that have done nothing wrong. A smell in your bathroom can be entirely a stack problem.
Unrecorded alterations. Someone, at some point, connected something to the stack that should not be there — a kitchen waste into a soil branch with no trap, a shower teed into a run with no fall, a macerator discharging into a pipe not sized for it. These produce recurring faults that no amount of clearing will resolve.
Noise. A soil stack running through the corner of a bedroom in a converted flat is a genuine amenity issue, and it is one of the more common complaints in refitted period stock. Boxing and acoustic lining can help; moving the stack usually cannot happen.
Planning work in a flat on a shared riser
If you are refitting a bathroom or a kitchen, five things to establish before anything is designed.
Where is the stack, and where can you connect? Every WC needs a route to the soil stack with adequate fall and acceptable pipe run. That constraint, more than anything, decides where a WC can go — which is why a re-plan that puts the WC on the far wall is often not a design choice but an impossibility. If gravity will not reach, the fallback is a macerator, with all its limitations.
What does your lease require? Most leases require freeholder or managing-agent consent for alterations, commonly through a licence to alter, and altering waste or soil connections is a typical trigger. Some leases treat any connection to a communal stack as requiring consent. Requirements vary between leases and between freeholds — and many freeholds in this area sit with large estates whose processes differ. Check yours rather than assume.
Who else is affected? Work on a riser can mean water off for other flats, or access through other flats. That has to be arranged, not improvised, and it usually means notice through the managing agent.
What are the building's rules? Contractor hours, booking, lift protection, waste routes, porter sign-in. All of it affects programme.
Is the riser itself past it? This is the one nobody wants to raise. If the block's stack is at the end of its life, a beautiful new bathroom hanging off it is a temporary arrangement. Worth asking the managing agent what the building's plans are before you spend.
Where the building does decide to renew a riser, that is communal works, and where the cost exceeds the statutory threshold per leaseholder, consultation under Section 20 of the Landlord and Tenant Act 1985 may apply. The managing agent will confirm how and when that runs.
Working with the managing agent rather than around them
The most useful thing you can do on a riser problem is get the diagnosis in writing. Managing agents deal in evidence. A clear note saying which pipe failed, where it sits relative to the duct, whether it serves one flat or several, and what caused it, is worth more than repeated phone calls. That is one of the more valuable things we produce on these jobs, and it costs you nothing extra.
The second most useful thing is timing. Communal repairs move at the pace of the block, not the pace of your Tuesday. If you can establish early that a problem is communal, you can start that clock rather than spend two weeks proving it individually.
How we handle riser work
We start by establishing what is yours and what is not, and we say so plainly, in writing, whether or not that leads to work for us. Where it is your branch, our plumbing work starts from £80 with a fixed price agreed before we begin, and we will put access hatches back rather than seal you into the same problem again. Where it is communal, we will help you evidence it for your managing agent.
For landlords and agents with flats across several blocks, planned inspection is a great deal cheaper than reactive attendance — our maintenance service and our page for agents and managers cover how that works. We operate across W1, W2, NW8 and W9; reach a plumber in Maida Vale or St John's Wood through the quote form.