Why Is My Roof Leaking Around the Chimney?

What you may be seeing inside

Chimney leaks tend to announce themselves in a fairly recognisable way, usually on or beside the chimney breast, often in a bedroom or on a landing, and often noticeably worse after wind-driven rain from one particular direction.

Common internal signs

• A damp patch on the chimney breast, upstairs or in the attic
• Staining that darkens during rain and fades between spells
• Tide marks or salt deposits on the plaster around the breast
• Damp appearing on the ceiling close to where the stack passes through
• Wet brickwork or timber visible around the stack in the attic

Possible causes of a chimney leak

The stack, the covering around it and the details that join the two are all candidates. In practice we often find two of these contributing together, which is one reason repairs based on a single assumption sometimes fail.

What may be at fault

• The flashing or soakers where the stack meets the roof — cracked, lifted, corroded or badly formed; see lead flashing
• Mortar joints that have deteriorated, allowing water into the masonry; see chimney repointing
• A cracked or weathered flaunching or cap on top of the stack
• Porous, spalled or frost-damaged brick or stone in the stack itself
• Slates or tiles around the stack that have slipped, cracked or been badly cut; see slate and tile repairs
• A back gutter behind the stack holding water or debris
• Water entering elsewhere and tracking down to show at the chimney

Why not every chimney leak is the flashing

Flashing gets the blame because it is the most visible detail, and it genuinely does fail — lead splits, mortar pockets release, and older cement fillets crack. But a stack with open joints can absorb water straight through the masonry and show damp internally with perfectly serviceable flashing in place.

Equally, repointing a stack that is being flooded by a failed back gutter will not stop the leak. The repair has to match the actual defect, which is why we look at the whole detail rather than the first thing that looks tired.

Disused and capped chimneys

A chimney that is no longer in use still has to keep water out, and unused stacks are often the ones that have been left longest without attention. Rain entering an uncapped flue, or a poorly sealed cap that traps moisture inside the stack, can both produce internal damp that looks exactly like a roof leak.

Where a stack is no longer needed at all, taking it down to below roof level and making the roof good is sometimes a more sensible answer than repeatedly repairing it. We will say so if that is the case rather than sell repairs to something you do not use.

How chimney leaks are usually repaired

The repair follows the defect. That might mean forming new flashing and soakers, cutting out and repointing deteriorated joints, renewing a flaunching, rebedding or replacing damaged coverings around the stack, or a combination of those.

Where a stack is leaning, badly cracked or looks unstable, we will tell you plainly that a specialist assessment may be needed before roofing work goes ahead. We are roofers, not structural engineers, and we do not pretend otherwise.