A chimney is one of the most common places for a roof to leak, and winter is when most chimney leaks show up. Heavy rain, wind and frost test every component of the stack — the lead flashing, the mortar joints, and the flaunching holding the pots. This article covers the typical causes and how we repair them.
Failed lead flashing
The lead flashing that seals the join between the chimney and the roof is the most frequent source of chimney leaks. Lead expands and contracts with temperature; if it was fixed without allowing for movement, or the wrong thickness was used, it work-hardens and splits. Heavy winter rain drives straight through the cracks. See our leadwork page.
Cracked flaunching
Flaunching is the mortar bed that holds the chimney pots in place. Frost and weathering crack it over time, and winter freeze-thaw widens those cracks until water runs down into the stack. Loose pots are a safety hazard as well as a leak source.
Weathered mortar joints
The mortar between the chimney bricks weathers faster than the bricks because the stack is fully exposed. As joints recede and crumble, water penetrates the stack, freezes in winter, and loosens the brickwork. Repointing restores and protects it. See our chimney repointing page.
Storm-damaged chimneys
High winds loosen pots, tear flashing and shift masonry. After a winter storm, a chimney that was sound can suddenly leak — or become unsafe. We make loose masonry safe as well as weathertight. See our storm damage roof repairs page.
Why the damp is not where the leak is
Water entering at the chimney travels down the stack and along timbers before it shows on a ceiling or wall. The damp patch is often below or to the side of the chimney, not directly under it. A drone inspection lets us see the chimney, pots and flashing close up to find the true entry point. See our roof leak repairs page.
Frequently asked questions
Why is water coming in around my chimney?
Water entering around a chimney is most often caused by failed lead flashing, cracked flaunching around the pots, or weathered mortar joints. We inspect the chimney, trace the true entry point, and repair it properly rather than patching the visible damp.
My chimney is leaking during heavy rain — what should I do?
Move belongings away from the damp and call us on 01622 611 499. We can inspect the chimney with a drone, identify the cause, and provide a written quotation for the repair.