A leaking chimney almost always traces back to one of four things — a cracked crown, a missing cap, failed flashing, or porous masonry. Finding the real source is the key to stopping the leak for good.
A cracked or crumbling crown
The crown is the concrete slab at the top of the chimney that sheds water off the masonry. When it cracks, water runs straight into the brick and mortar. Sealing or rebuilding the crown is often the fix.
A missing or damaged cap
Without a cap, rain falls directly down the flue, rusting the damper and soaking the interior. A properly fitted cap is a simple, inexpensive fix.
Failed flashing at the roofline
Flashing is the metal seal where the chimney meets the roof. When it corrodes or pulls away, water gets in at the roofline — a very common leak point that is often mistaken for a roof problem.
Porous or damaged masonry
Old brick and mortar absorb water like a sponge, especially once mortar joints fail. Repointing and a breathable masonry sealant stop the water without trapping moisture inside.
Chimney leaking after every storm?
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Call (708) 432-5330Frequently asked questions
How do I know where my chimney is leaking?
An inspection pinpoints the source — crown, cap, flashing, or masonry. Sealing the top without finding the real cause rarely lasts.
Is a chimney leak actually a roof problem?
It is often mistaken for one. Failed flashing where the chimney meets the roof is a frequent leak point that a chimney technician addresses.
Can I just seal the top of the chimney?
Sealing without fixing the cause can trap water inside and make things worse. The leak source has to be identified and repaired first.
Why does water damage matter so much?
Water is the number-one cause of chimney deterioration. Left alone, a small leak leads to spalling brick, a failed crown, and eventually an unsafe chimney.
Written by Adam Evans, owner of Chimney Sweep Brothers and a chimney technician with 12 years of experience serving La Grange, IL and the western suburbs.