Why Is My Chimney Leaking? | Lexington Masonry Pros

Why is your chimney leaking when the roof is fine? In Lexington, KY, it’s almost always the crown, the flashing where the chimney meets the roof, or open mortar joints — not the shingles.

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Why Is My Chimney Leaking When the Roof Is Fine?

Most often the crown, the flashing where the chimney meets the roof, or open mortar joints — not the roof covering itself. Those three are the first things a mason checks, in that order.

The Crown

The crown is the concrete or mortar cap on top of the chimney, and it’s built to shed water away from the flue and the masonry below it. Once it cracks, water sits in the crack instead of running off — and every freeze-thaw cycle through fall and winter widens that crack a little more. A failed crown sends water straight down through the chimney structure, which can show up as a stain on a ceiling nowhere near the roofline. See chimney cap and crown replacement for what repair or replacement involves.

The Flashing

Flashing is the metal seal at the joint where the chimney meets the roof deck, and it’s a common leak point precisely because two different materials move at different rates as temperatures change. Nails back out, sealant dries and cracks, and a gap opens that lets water run down the chimney’s exterior and into the attic or wall cavity below. Full diagnosis and repair is covered in our chimney flashing repair guide.

Open Mortar Joints

Brick itself is somewhat porous, but sound mortar joints keep water from tracking through the wall. Once joints are recessed, cracked, or missing, the chimney absorbs water directly through its face — and in Kentucky, that water freezes and expands inside the masonry through the winter, which is exactly how a slow leak turns into spalling brick and a much bigger repair. Our tuckpointing and repointing guide covers how that gets fixed.

What Diagnosing and Fixing a Chimney Leak Typically Costs

Chimney leak repairs in the Lexington area typically run $250–$1,200 depending on which of the three culprits is involved and how much masonry work it needs — that’s a typical range, not a quote; a proper diagnosis before any work starts is how you avoid paying to fix the wrong thing. Full pricing context is in our masonry cost guide.

For general chimney maintenance and safety background, the Chimney Safety Institute of America publishes homeowner resources on chimney upkeep.

Common Questions

Can a chimney leak without any visible crack?

Yes. Hairline crown cracks and slightly lifted flashing nails are easy to miss from the ground but are common leak sources — a close-up inspection catches what a glance from the yard won’t.

Does a chimney leak get worse in winter?

Usually, yes. Water that gets into a crack or open joint freezes and expands, widening the opening — so a small fall leak often becomes a bigger problem by spring if it isn’t addressed first.

Should I fix the crown, flashing, or mortar first?

Whichever is actually letting water in — fixing the wrong one leaves the leak in place. That’s why a proper diagnosis of all three before any repair starts matters more than guessing.