Why is my downpipe leaking where the sections join?
Downpipe joints are meant to be loose push-fits, not sealed. A joint that leaks is usually blocked, misaligned or assembled the wrong way up.
- Difficulty
- beginner
- Time
- 30 min
- Read
- 2 min
- Safety
- caution
Short answer
Check the joints are the right way round — each section should sit inside the one below, so water cannot escape at the overlap. Then check the pipe is not blocked, because a surcharged downpipe leaks at every joint. Sealing the joints is almost always the wrong fix.
A downpipe is a series of loosely fitted sockets, deliberately. It has to be able to expand, contract and be dismantled for clearing. So a leaking joint is rarely a failed seal — there usually was not one — and is nearly always telling you either that the assembly is wrong or that the pipe is running full when it should not be.
Safety
Step by step
- Check which way the sockets face.Each length should push down into the socket of the section below, so water runs from the inside of the upper pipe into the lower one. Assembled the other way round, water runs out at every joint. It is a surprisingly common error after a repair.
- Look for a blockage before anything else.A downpipe leaking at several joints at once, or only in heavy rain, is surcharging. The water is backing up and finding the joints. Clear it and the leaks usually stop.
- Check the pipe is properly supported and vertical.Loose or missing brackets let sections pull apart at the sockets, and a pipe leaning away from the wall opens the joints on one side.
- Check the joint is fully home.Sections work loose over time, particularly where there is thermal movement or where a bracket has failed. Push the joint back together and refix the bracket.
- Look at the top of the pipe as well.The swan neck from the gutter outlet is where blockages start and where offsets are most easily knocked out of line.
- Do not seal downpipe joints.They need to come apart to be cleared, and they need to move. Sealing them makes the next blockage far harder to deal with and does nothing about the cause.
- Watch what the leak is landing on.A joint dripping onto a wall in one spot for years is a genuine damp risk, and the repair urgency depends more on that than on the volume of water.
Common mistakes
- Running sealant round the joints. — It treats a symptom of a blockage, prevents dismantling for clearing, and traps water inside the joint where it can freeze.
- Assembling the pipe with the sockets pointing upwards. — Water then runs over the outside of the lower section at every joint. It looks tidy and leaks constantly.
Questions people ask
Should there be a seal in a downpipe joint?
Generally no for standard round or square downpipe — they are loose push-fits by design. Some proprietary and cast-iron systems differ, so check what you have before adding anything.
It only leaks in heavy rain — is that normal?
No, but it does tell you the cause. It means the pipe runs full in heavy rain, which points to a restriction below or a system at capacity.