Leak around the soil vent pipe on the roof

1How the pipe gets through the covering

A soil and vent pipe carries drain air up and out of the house, so it has to rise through the roof. The covering stops at the pipe, which leaves a hole that must be sealed in a way that sheds water down the slope.

There are three common ways. The first is a lead slate: a sheet of lead that sits under the tiles above and over the tiles below, with a collar of lead dressed up round the pipe. The second is a flexible collar, a cone of EPDM rubber or similar, clamped round the pipe and fixed to a base plate. The third is a pipe tile, a one-piece moulding shaped like the surrounding tiles with a sleeve built in.

Which one suits depends on the covering. Slate and plain tiles take a lead slate well, while an interlocking tile often has a matching pipe tile made for its profile. A flashing is simply the shaped metal or rubber that seals the join, and a soaker is a small tucked piece of lead that carries water over the edge of a joint.

2Where these seals fail

Rubber collars perish with age and sunlight. The neck, where the cone grips the pipe, cracks first, and rain then runs down the outside of the pipe into the loft. A clamp that has loosened lets the collar ride up the pipe, with the same result.

Lead slates fail differently. The lead lifts at its edges, splits along a fold, or was fitted badly in the first place, with its top edge not tucked under the course above, so water running down the slope gets behind it. Pipe tiles slip or crack, and a cracked tile is simply a hole.

Sealant over any of these is a common earlier attempt. It can hold for a few weeks and then traps water behind a split, which is why the repair described below never relies on it.

Sometimes the pipe itself is the problem. An old cracked pipe leaks inside the loft, and that is drainage work for a plumber, while the roof seal stays our job. A nest or debris in the open top is a separate issue; see birds nesting in the roof.

3Is it a leak or condensation?

The pipe carries warm, damp air through a cold loft, and the cold surface of the pipe collects moisture. It runs down the outside and drips at the base, leaving a ceiling stain that looks exactly like a leak at the pipe.

The difference shows in the loft with a torch. A leak leaves a stain that stops at the entry point, with wet timber and tide marks on the roof side of the collar, and the stain grows after rain. Condensation leaves the pipe wet along its length, shows up in dry spells as well, and gets worse in cold weather when the pipe is coldest.

Both can happen together, and both are fixable. Lagging the pipe cuts the condensation, and a good collar or flashing stops the rain.

We trace from the inside first and then check the outside, so the repair goes where the water actually comes in rather than where the stain sits on the ceiling. It is the same habit we bring to every leak, and it saves replacing a perfectly good collar.

4What a proper repair involves

A failed rubber collar is replaced with a new one that fits the pipe and its base plate, not coated over. If the base plate is bent or the tile around it is broken, those are put right at the same visit.

For lead, a new slate is cut and dressed to the roof. Code 4 lead is the usual weight for general flashing, and the sheet is made to BS EN 12588. The top edge is tucked under the course above, the lower edge laps over the tiles below, and the collar is dressed tight to the pipe. A cracked pipe tile is renewed with one that matches the existing profile.

The pipe is rarely within safe ladder reach, and a tube of sealant from a shop seldom solves it, as the guide to DIY roof repair sets out. On a listed building, a repair that does not match the existing materials can need listed building consent, so listed roof repairs is worth reading first. The wider range of roof work is under roof repairs.

5Cost drivers for a pipe seal

The job varies in size. A collar swap on a low roof is quick. A lead slate on a steep slate roof, reached by tower or scaffold, calls for more work, and a wet ceiling or damp insulation below may need attention too.

Access is often the largest single factor, since a pipe high on a steep slope changes how we reach it. The covering matters as well, as does whether we are replacing a collar or relaying the surrounding lead.

Survey photographs of your own pipe and roof come to you first. The survey is followed by a written quote showing one price for the job as found. If two quotes for the same pipe differ a lot, why roof repair quotes vary explains the usual reasons.