Chimney Flashing Repair Guide

Why chimney flashing fails so often

A chimney is rigid masonry sitting through a roof made of flexible shingles — two very different materials that expand, contract, and settle at different rates over time. Flashing is the engineered solution: a system of interlocking metal pieces designed to shed water even as everything shifts slightly around it. Done right, it's very durable. Done poorly — a common shortcut is simply caulking or tarring the joint instead of properly flashing it — it fails within a few years, because sealant alone can't handle ongoing movement and UV exposure the way metal flashing can.

The two flashing types that should both be present

• Step flashing: individual L-shaped metal pieces, one per shingle course, woven into the roof along the sides of the chimney so each piece overlaps the one below it like shingles themselves.
• Counter flashing: a second layer of metal set into a cut mortar joint (or under a reglet) in the chimney itself, overlapping down onto the step flashing to create a two-part, water-shedding seal rather than relying on a single layer.
• Cricket (saddle): for chimneys wider than about 30 inches on the up-slope side, a small peaked structure (a cricket) is required to divert water and debris around the chimney instead of letting it pool against the uphill face.
• Sealant: used to finish and protect flashing edges, but sealant should support the metal flashing system — not replace it.

Pro tip from our network contractors

If a previous fix on your chimney is a thick bead of roofing cement or tar smeared over the joint instead of visible metal flashing, treat that as a warning sign, not a repair — it's a common patch that buys a little time but reliably fails again within a few years.

Signs of a flashing failure — and what repair costs

Watch for water stains on the ceiling or wall near the chimney, visible rust or gaps in the flashing metal, cracked or missing mortar around the counter flashing, or daylight visible around the chimney from inside the attic. A straightforward flashing repair (resealing or replacing a section) typically runs $300–$700; a full flashing system replacement, especially if it requires masonry work like re-cutting mortar joints, can run $700–$1,500 or more. If your roof is nearing the end of its life anyway, it's often more cost-effective to replace the flashing as part of a full roof replacement rather than paying for it twice. See how long does a roof last and roof repair vs. replacement to weigh that decision.