How flashing works — and how it fails
Proper chimney flashing is usually two layers: base flashing (or step flashing) that laps under the shingles and up the chimney, and counter-flashing that’s let into the masonry and folds down over the base flashing. Together they create a seal that sheds water even as the roof and chimney expand, contract and shift at different rates.
It fails when:
- The sealant/caulk at the counter-flashing dries out, cracks and lets water behind it (extremely common — and often mistaken for a lasting fix when someone just re-caulks it).
- The metal corrodes — a real issue in salt air — or lifts and separates in high wind.
- It was never installed correctly: surface-mounted and caulked instead of set into the masonry, or missing a layer entirely.
- A roof was replaced and the old flashing was reused or poorly reintegrated.
Why we confirm the source first
A leak near the chimney isn’t automatically a flashing leak. Water can also come from a cracked crown, a missing cap, failed mortar joints, or a rusted chase cover — and it can travel a long way before it drips. So we diagnose the actual entry point before repairing, because sealing the flashing won’t stop a leak that’s coming from the crown. This is really a leak diagnosis job that often ends at the flashing.
Repair done right vs. a caulk smear
The quick “fix” a lot of homeowners have seen is a bead of roofing tar or caulk over the flashing. It looks sealed and lasts a season. A proper repair either renews the counter-flashing seal correctly or replaces the flashing with new metal — appropriately lapped, set into the masonry, and sealed to last, not just smeared. On a coastal home we favor corrosion-resistant metal so the repair survives the salt air that killed the last one.
Flashing and your roofer
Flashing lives at the intersection of two trades. When a roof is being replaced, that’s the ideal moment to get the chimney flashing done properly, and we’re happy to coordinate. If your leak appeared right after a re-roof, the flashing integration is a prime suspect. We’ll tell you honestly whether what you have is a chimney fix, a roof fix, or a bit of both.
Questions people ask us
My ceiling stains near the chimney every time it rains hard — is it the flashing?
Flashing is the most common cause, but not the only one — a cracked crown, missing cap, open mortar joints or a rusted chase cover can all leak in the same spot. That’s why we trace the actual entry point first. If it turns out to be flashing, we fix it properly rather than just re-caulking.
Someone already put tar over my flashing — why is it leaking again?
Tar and caulk over flashing are temporary by nature; they dry out, crack, and let water back in, usually within a season or two in our sun. A lasting repair renews the counter-flashing seal correctly or replaces the metal, rather than relying on a surface smear.
Should my roofer or a chimney company do the flashing?
Either can, but flashing done as an afterthought — reused during a re-roof or surface-caulked — is where leaks start. It’s worth having it done properly by whoever will integrate it correctly into both the roof and the masonry. If you’re re-roofing, that’s the natural time to get the chimney flashing right, and we can coordinate.