In short
A damp patch on a chimney breast is water coming down the stack from the roof, not rising from the ground. It gets in through split or lifted lead flashing, open mortar joints in the brickwork, a cracked flaunching at the top, or an open pot on a disused flue. The pattern of the stain, and whether it follows heavy rain, tells us which.
This is a job for our Chimney repairs service.
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Where the water is getting in
A chimney is a brick tower standing above the roof in the open, and on the Norfolk coast it takes the weather from every side. Water gets into a stack in four places, and each leaves a different stain inside.
| Where it gets in | What you see inside | What we usually find |
|---|---|---|
| Lead flashing at the roof line | Stain low on the breast, in the loft or at ceiling level, worst after wind-driven rain | Lead split along its fold, stepped flashing pulled out of the joint, or a mortar fillet used instead of lead |
| Brickwork joints | Broad damp area across the breast, slow to dry | Mortar weathered back so the joints hold water, sometimes a whole face soft |
| Flaunching and pot | Damp high up, or in the bedroom nearest the stack | Cracked cement around the pot, rain falling straight down an uncapped flue |
| Condensation in the flue | Brown, tarry stain that smells, often on a blocked-up fireplace | Flue sealed at the bottom and capped at the top with no vent, so it never dries |
How to narrow it down before you call
- Does it get worse after rain? If yes, it is one of the first three. If it is much the same all year, suspect condensation.
- Where is it on the breast? Low down points to the flashing. High up points to the top of the stack.
- Is the fireplace blocked up? A flue with no air through it sweats, and the stain is the tar in the old soot coming through.
- Look at the stack from the garden. Missing mortar and a lean are visible from the ground. Do not go up to look closer.
What we do about it
We go up and look, because a chimney cannot be diagnosed from a stain. The repair is whichever of the four applies. Split lead is cut out and renewed in new lead, dressed into a raked joint, not sealed over with mastic. Open joints are raked out and repointed. A cracked flaunching is taken off and re-formed. A disused flue gets a vented cap so it stays dry but can breathe. Where the top courses have blown apart from frost, which is common on the older stacks in Cromer, Sheringham and along the north coast, the honest answer is to take the stack down to sound brick and rebuild it.
Checkatrade's 2026 chimney repair guide puts most repairs between £180 and £1,000 depending on the work, with flashing repair at £250 to £1,000 and repointing at £300 to £1,000 once scaffolding is included. Access is the biggest variable in that range. A stack on a low back roof is a ladder job; one on the ridge of a two-storey house needs a scaffold.
