How often should chimney flashing be replaced?
Short answer. Chimney step flashing should be replaced every time the roof is replaced, while well-installed counterflashing set into the mortar can often stay if it is sound. Flashing needs attention sooner if it rusts, pulls out of the mortar, or depends on sealant that has cracked.
Step flashing: every reroof
Step flashing is woven between shingle courses, so it cannot be reused cleanly once the shingles come off. Bent-back old pieces carry nail holes and kinks, and reusing them is one of the most common causes of chimney leaks on new roofs. Plan on new step flashing, apron and back pan with each replacement, which on a Georgia asphalt roof usually comes around every couple of decades.
Counterflashing: inspect, then decide
- Can stay: counterflashing properly cut into a mortar joint, still tight, not rusted, and long enough to cover the new step flashing.
- Should go: counterflashing that is surface-mounted and caulked to the brick face, rusted, too short, or pulled loose. Replacement means cutting a new groove into the mortar.
By metal
- Galvanized steel: eventually rusts where the coating wears, especially behind trapped debris.
- Aluminum: does not rust, but can corrode where it sits against wet mortar without a protective coating.
- Copper: can outlast several roofs if left undisturbed.
Signs it is due before the next roof
- Ceiling or wall stains beside the chimney, especially after wind-driven rain.
- Gaps between the counterflashing and brick, or thick tar patches covering the joint.
- Rust streaks on the shingles below the chimney.
- Water pooling or debris piling behind a wide chimney with no cricket.
The sealant along the top of counterflashing is maintenance, and it may need renewing every few years even when the metal is fine. See chimney leaks and crickets and roof flashing explained.