Do this first
- Stop using whatever feeds it. A soil pipe only carries water when something above is draining, so pausing the WC, bath or basin that feeds that run stops the leak immediately.
- Work out which appliance it is. Dry the joint, put paper under it, then run each fitting above in turn: flush the WC, run the bath, empty the basin. The one that wets the paper is the one on that branch.
- Electrics first if the pipe is boxed in beside a consumer unit, a socket or a light. Switch that circuit off before opening any boxing.
- Treat it as contaminated. Gloves, ventilate the room, keep children and pets away, and do not use a household vacuum on it.
- If it is an internal stack in a cupboard or boxing, open just enough to see and look at the joints rather than the pipe body. Almost all of these are at a socket joint or a branch connection.
- Photograph it, including where the pipe runs and which flats or rooms it passes. That evidence decides who pays.
Which joint, and whose pipe
Two questions here. What is leaking, and who owns it, and the second one often matters more than the first.
| Observation | Cause |
|---|---|
| Wets only when one appliance drains, at a branch connection | Branch seal, a dropped or unsupported branch, or a boss that was cut badly |
| Wets whenever anything above drains, at a socket joint on the stack | Failed ring seal, or a joint pushed apart by thermal movement |
| Weeping from a cracked pipe body, often near a bracket or a bend | Impact damage, a pipe under strain, or an old cast iron stack corroding |
| Smell but no visible water | A dry trap or a failed air admittance valve rather than a leak |
| Stains on an external wall beneath a joint, worse in heavy use | External stack joint, usually the freeholder's in a block |
Ownership follows the route. A branch inside your flat that serves only your fittings is normally yours. The stack itself, the vertical pipe collecting several flats, is usually structure and therefore the freeholder's or the block's, and that is true whether it runs up the outside wall or is boxed into a cupboard in your bathroom. It is worth establishing before anyone is instructed, because a leaseholder who pays for a stack repair out of their own pocket rarely gets it back afterwards.
Tenants have a simpler answer: drains, gutters and external pipes fall within the landlord's repairing obligation for the structure and exterior, along with the installations for sanitation. Report it in writing and let them instruct. If water is arriving on a ceiling rather than showing at the pipe, a water stain on a ceiling and a leak from the flat above cover the attribution side.
What the repair involves
Modern plastic stacks are repaired by remaking the failed joint with a new seal, or by cutting in a slip coupling where the run has moved, then re-bracketing the pipe so it is supported rather than hanging on its joints, which is what caused the failure in most cases. Cast iron stacks in older London buildings are a different job: corroded sections are cut out and replaced, and where the whole stack is at the end of its life, patching one joint simply moves the leak up a metre.
Boxing, tiling, plaster and decoration are put back afterwards, and where waste water has been running into a floor or a ceiling void, that gets stripped, cleaned, dried and reinstated rather than boxed back over. Contaminated water in a building fabric is not something to close up and forget. That whole scope is pipework repair and replacement, and our rate for it is on the pricing page.
When it is not us
- It is the shared stack in a block. Report it to the managing agent or freeholder in writing today. It affects every flat on that stack, and you should not be paying for it personally.
- Smell with no water. A dry trap, a failed air admittance valve or a missing stack vent. Worth fixing, but it is not a leak.
- Waste backing up rather than leaking out. That is a blockage, and below ground it may be the sewerage company's responsibility rather than yours.
- The pipe is on the outside face of the building. External pipework on a block is normally the freeholder's, and the same applies to rainwater goods that run alongside it.
- You rent. Report it in writing straight away. Drains, gutters and external pipes are the landlord's under their repairing obligation.
- The whole cast iron stack is corroded. That is a planned building repair, usually through the service charge in a block, not an emergency call-out.