First steps if water is coming in
- Put a bucket or tray under any drip and move belongings away from the wall.
- If there's a fireplace, don't light it until the stack has been checked.
- Look in the loft, if it's safe, for wet timbers or water running down the brick.
- Take photos of the stain and note when it appears: after any rain, or only storms.
Don't climb onto the roof yourself. Chimneys sit at the most exposed point of the house and are dangerous to reach without proper access.
Where chimneys let water in
Flashing at the base
The joint between the stack and the roof is sealed with lead flashing tucked into the mortar. When the lead splits, lifts in the wind or works loose from its joint, water runs straight behind it. This is probably the single most common source. Our lead flashing repair page covers how it's put right.
Mortar joints
Recessed or crumbling pointing lets rain soak deep into the brickwork, where it tracks down inside the stack and appears as damp below. Renewing the joints is explained on our chimney repointing page.
Flaunching and pots
The sloped mortar bed at the top holds the pots in place and sheds water off the stack. Once it cracks, water sits in the gaps and runs down the inside.
Open flues
A disused flue with no cap is effectively a pipe for rain. Fitting a ventilated cap stops the water while still letting the flue breathe.
Back gutters and the uphill side
Where a stack sits partway down a slope, water running off the roof above hits the back of it. If the lead back gutter there is worn or blocked with debris, it overflows.
Chimney leaking when it rains, or something else?
Not all chimney breast damp is a leak. Condensation inside an unventilated, capped flue can stain plaster, and salts from old soot can draw moisture out of the air. A leak tends to follow rainfall closely; condensation is more constant and worse in cold weather. If the damp is elsewhere on the ceiling, our roof leaking page may fit better.
How we trace the source
We start by looking at the stack from the ground and the loft, then get proper access to inspect each face, the flashing, the flaunching and the back gutter up close. Where the cause is clear, we explain it and quote for that repair. Where several things are worn, we'll tell you which matter most so you can decide what to do now and what can wait.
Damage a chimney leak can cause
Water from a chimney often soaks into the brickwork and timbers around it long before it shows on a wall. Rafters and joists beside the stack can rot, plaster can blow and salts can leave lasting stains. Dealing with the cause early keeps the repair to the stack rather than the rooms below. If you're on a terrace, it's also worth mentioning to neighbours, since a shared stack can affect both homes.
Repair or remove?
Most leaking chimneys are repaired. But if a stack is redundant and needs a lot of work, taking it down below the roofline may be worth considering; our chimney removal page explains what that involves.
Need it sorted? Book a chimney repair
We work across Somerset and Devon, within about 50 miles of Taunton. See our chimney repair service, call 07399 680142 or request a free written quote.