The short answer
A roof usually leaks around a soil pipe because the seal where the pipe passes through the covering has failed. The flashing, collar or lead sleeve may have cracked, lifted or split with age and weather, letting rain run down the outside of the pipe into the house. Sometimes a displaced tile or a cracked pipe is to blame. The usual fix is to renew the weathering, not the pipe.
Why that spot leaks
A soil pipe, or vent pipe, rises from the drains inside the house and finishes above the roof so that gases can escape. Wherever it passes through the covering, the roof has a hole, and that hole has to be sealed against rain. Every pitched roof with a pipe has this weak point, because roofing materials flex, shrink and age, while a rigid pipe stays still.
Water finds the gap. It runs down the outside of the pipe, through the break in the seal, and onto the felt or the timber below. From there it can travel along a rafter before it shows itself as a stain on a ceiling, sometimes a good distance away. That is why the stain and the hole often do not line up, a point we cover in how to find a roof leak.
The fault is usually in the weathering, not in the pipe itself, which is why replacing the pipe rarely cures a leak. The cure is to deal with how the roof meets the pipe.
The common causes
Several faults account for most leaks of this kind, and a roofer works through them in turn.
- A perished rubber or plastic collar. Many modern roofs use a flexible boot that fits over the pipe. Sunlight hardens it, and it splits where it bends. After a crack forms, rain follows the pipe down into the roof space.
- A lifted or split lead sleeve. On older and period roofs the pipe is usually sealed with sheet lead, shaped around it and dressed onto the tiles. Lead can crack at the folds, and if the upper edge lifts in wind, rain gets behind it.
- A slipped or cracked tile or slate next to the pipe, which opens a path beside the weathering.
- Sealant that has failed. Mastic or silicone applied as a quick fix shrinks and pulls away within a few seasons.
- A cracked pipe or loose joint above the roofline, where water enters the pipe itself.
Sealant over a failing lead sleeve is a common example of a repair that buys a short reprieve, then leaves a worse job to do. Our page on like-for-like repairs explains why we replace the weathering with the same type.
How the cause is found
We start inside. A torch in the loft shows a water track on the pipe, the rafters or the underlay around it, and a damp meter or a clean, dry cloth confirms what is wet. Then we go outside and look closely at the collar, the lead, the surrounding tiles and the top of the pipe.
It matters to separate a roof leak from condensation, because a vent pipe is colder than the room around it and moisture forms on it. Water that forms in the loft in cold weather and dries up in warm spells points to condensation, while water that appears after rain points to a leak. If that distinction is unclear, leak or condensation describes how we tell them apart.
Because pipes often sit high on the slope or close to a ridge, a cheap look from the ground is not enough. Binoculars and photographs help, but the repair itself needs hands on the roof.
How the leak is repaired
The repair depends on the cause. For a perished collar, the old boot is cut away and a new one fitted, with the surrounding tiles lifted and relaid so the upper edge tucks beneath them and the lower edge laps over, which is what lets rain drain away from the pipe. For a lead sleeve, a new piece of lead is cut, shaped and dressed. It is usually a better answer than patching, and lead is the traditional material on older properties in Bath.
If a tile or slate is cracked, it is replaced with one that matches the rest of the slope. Any wet felt or batten that has gone soft is cut out and renewed, because new weathering on bad timber will not last.
A leak at a pipe is typically a small repair in terms of materials, so in the cost guides it falls into the minor repair range. MyBuilder's 2026 guide puts small repairs of this sort at £100 to £300. That is a typical UK range, not an Empire price, and we quote a fixed price for your own roof after surveying it.
Access, urgency and what to do now
Pipes tend to rise through the roof high up, and the height can decide how the job is done. A pipe low on a rear extension can sometimes be reached by ladder. One on a tall house or near the ridge may need a tower or scaffold to work from safely, which our note on repairing a roof without scaffolding explains.
Meanwhile, set a bucket beneath the drip, shift belongings clear and watch the ceiling for any bulge. If water is reaching a light fitting or other electrics, turn the circuit off at the fuse board and read what to do about water at a light fitting. A leak that is running now is covered in emergency roof leaks.
We survey first, send photographs of your roof and agree a written price before work starts. Until then, watch the ceiling around the pipe boxing and note whether the stain grows after rain or after the bathroom is used, as that points to the cause. For other faults of this kind across the area, the roof repairs in Bath hub lists what we cover.
