In short
A leak next to a chimney is almost always the lead flashing or the mortar joints on the stack, not the roof tiles around it. The usual culprits are a back gutter that has lost its fall, a cracked or lifted apron at the front, or soakers that have slipped under the tiles. We strip the leadwork back, check the brickwork and pointing, and re-dress new lead rather than smear sealant over the old.
This is a job for our Chimney Repairs & Rebuilds service.
What is actually letting the water in
The chimney is the one place on a pitched roof where four separate pieces of lead have to work together, and any one of them can fail on its own. The Lead Lads' guide to chimney flashing lists the parts: soakers under each course of tile at the sides, step flashing dressed over them into the brickwork, an apron across the front, and a back gutter behind the stack that carries water round it. The same guide puts a poorly formed back gutter, with no fall and no overflow, at the top of its list of leak causes, followed by flashing that has pulled out of a shallow chase and aprons that have crept and rippled because they were pinned too tightly to move.
On the older houses we work on around Spalding, Holbeach and Boston there is usually a second problem underneath. Lime or sand-and-cement pointing on the stack has weathered back, so rain is soaking through the brick itself and running down inside the chimney breast. Customers see a damp patch on the chimney breast wall, assume the roof is leaking, and are half right.
How we tell the difference
We look at the stack from the roof, not from the ground, and we look in the loft on a wet day. A leak from the back gutter shows as a wet line on the rafters directly behind the stack. Failed soakers show as damp on the timbers to one side. Porous brickwork shows as a wet chimney breast with dry rafters. Each has a different fix, which is why we do not quote from a photograph.
What we do about it
- Re-dress the leadwork. We strip the old lead, cut a proper chase into the mortar joint, and fit new soakers, step flashing, apron and back gutter in the lead code that suits each part. Checkatrade's 2026 roof repair guide lists replacing defective stepped lead flashing in Code 5 at £80 to £120 per metre and plain flashing at £50 to £70, before access equipment; ours depends on the height of the stack and whether we need a scaffold tower.
- Repoint or rebuild the stack. If the pointing has gone we rake it out and repoint. If the brickwork is spalled or the stack is leaning, we take it down to sound brick and rebuild it, as we did on the twin stacks pictured on our chimney page.
- Take it down if it is doing nothing. A stack that serves a blocked-off fireplace is a leak waiting to happen. Removing it below the roofline and tiling over is often cheaper than rebuilding it.
What we will not do
We do not run a bead of mastic round old lead and call it fixed. It holds for a season and then you are paying twice. Our repairs are guaranteed for five or ten years depending on what has been put right, and sealant would not survive that.