Leaking chimney
Why does my chimney leak when it rains?
The short answer
A chimney leaks in rain because water finds a gap somewhere along its height. The usual culprits are the lead flashing at the roof junction, the mortar crown on top called the flaunching, worn pointing between the bricks, and a cracked pot. Where the damp shows inside, on the breast or in the loft, points towards which one. A roofer should find the entry point before anything is replaced.
Where rain gets in around a chimney, how to read the clues from inside the house, and what a sensible repair involves.
Read the clues indoors first
A chimney is a tall, exposed column of brick pushed through the busiest part of the roof, so it offers water more routes in than any other roof feature. The stain on your ceiling is seldom directly under the hole, because water runs along timber and tile before it drops. The mark tells you which side of the stack to examine, not the precise spot.
Useful clues cost nothing. A brown patch on the breast in the bedroom that worsens after driving rain suggests the stack itself is soaking. Dampness on the ceiling beside the breast suggests the flashing. Wet timber around the stack, visible with a torch from the loft hatch, narrows it further. Note the weather when it leaked and take photographs, since we use them at the survey. Say whether the drip started as soon as the rain did or an hour or two later, because that delay hints at how far the water has travelled. Our page on water around a chimney in the loft goes through the loft check step by step.
The flashing: the seam between stack and roof
A flashing is a length of sheet metal, normally lead, that bridges the joint between brickwork and roof covering. Around a chimney it comes in parts: an apron on the low side, stepped pieces up each flank that tuck into the mortar joints, plus a back gutter tucked behind the stack to send water round it. Soakers, little folded sheets slipped under each tile or slate beside the stack, complete the junction.
Failure tends to start at the edges. The mortar holding the lead crumbles, the lead lifts or splits where it has been bent repeatedly, or somebody has smeared sealant across a gap that needed a real repair. Sealant buys a season or two at best. Lead dressed into raked-out joints and pointed can last for a very long time, and MyJobQuote says flashing can last for over 80 years. Our pages on chimney flashing and the back gutter show each part.
Flaunching, pointing and the pot
The flaunching is the sloping crown of mortar at the very top of the stack. It anchors the pots and throws rain outward. If it cracks, or shrinks away from a pot, water slips into the gap and runs down through the flue and the brickwork beneath. Because the damage can be a hairline, it is hard to spot from the ground, yet in a gale it can feed a surprising amount of water into the stack.
Pointing means the mortar that fills the joints between bricks. Once it has eroded, rain soaks into joints and bricks and the wall stays wet long after the sky clears. A cracked pot admits water from above in the same way. Caught early, each of these is a small local repair, which is why we inspect the whole stack and not just the corner that drips. Our guides to chimney flaunching and chimney repointing describe how those repairs go.
Coping until the repair can happen
If water is coming in now, protect the room. Move furniture, set a bowl under the drip, and if the ceiling is bulging, a small hole made with a screwdriver lets the water out gradually and not all at once. Stay off the roof, and politely turn away anyone who offers to climb up in poor weather with a tub of sealant.
A wet ceiling moves a job up our list, and the first visit is about stopping more water coming in, which can mean a temporary cover until conditions allow the proper repair. When a storm caused the damage, Which? advises contacting your insurer before anything else, taking photographs and holding on to receipts for emergency work. Keep damaged items for the insurer to inspect, unless they are hazardous. Our page on chimney storm damage lays out the order, and the repair afterwards is sized to the fault found.
What a proper repair involves and costs
The cost follows the cause. MyJobQuote, last updated in September 2026, gives typical UK figures of £150 to £250 for a patch of lead and £350 to £460 for a full set of chimney flashings without scaffold, rising to £700 to £920 when scaffold is needed. Those are national guide prices. Ours is set once the roof has been surveyed, and it arrives as a single written price, so you know where you stand before any work begins.
On site the sequence is usually: expose the faults, cut out failed mortar, renew the lead or the flaunching, repoint, then check that water now runs where it should. We photograph every stage, which lets you check what was done, and any timber that has stayed wet is pointed out so it can be checked again once the weather turns dry. If the stack is too far gone to patch, we show you why, and the job moves towards a rebuild. Read about chimney stack rebuilds if the brick itself is failing, or return to the main chimney repairs page.
Related questions
Wet chimney queries
If it only leaks on windy days, is it the flashing?
Often, yes, because wind drives rain sideways into a gap in the lead or the edge mortar that stays dry in still weather. It can also be pointing on the windward face. A survey from the roof, with photographs of each junction, separates the two.
Can I seal a leaking chimney myself?
Sealant over a failed joint may slow a leak briefly and hides the fault from the next person looking. It also makes proper repair harder, because lead and mortar have to be cleaned back first. Climbing onto a wet roof is the greater danger.