Flashing is the metal that seals the joints where the roof meets a chimney, wall, vent, or valley — and because these transitions are where water concentrates, flashing is one of the most common leak sources on a roof.
Inspect the flashing
Check flashing around chimneys, plumbing vents, skylights, and in valleys for rust, cracks, lifted edges, gaps, and dried-out or missing sealant. Loose or corroded flashing lets water sneak under the roofing.
Minor repairs
Small gaps and lifted edges can be re-sealed with roofing cement or a compatible sealant, and loose flashing re-secured. Replace a small section of corroded flashing where needed. Re-bedding loose mortar (counter-flashing) at a chimney restores the seal.
When to call a roofer
Extensively corroded or improperly installed flashing, chimney flashing that needs step-flashing rebuilt, and active leaks you can't trace are jobs for a roofer. Flashing done wrong leaks again, so it's worth getting right.