Counter Flashing

What Is Counter Flashing

Counter flashing is a metal piece that overlaps the top of base flashing or step flashing from above, creating a two-layer waterproofing system at vertical wall and chimney intersections. While base flashing turns up from the roof surface against the wall, counter flashing is attached to the wall itself and folds down over the base flashing. This overlap means water running down the wall face hits the counter flashing first, then drains onto the base flashing, and then onto the shingle surface. The two pieces are not sealed together, which is intentional. The gap between them allows the roof and wall to expand and contract independently without breaking the water seal. Counter flashing is also sometimes called cap flashing, particularly in commercial roofing terminology.

Counter Flashing Installation Methods

On masonry walls and chimneys, counter flashing is embedded into a mortar joint. The installer cuts a horizontal groove, called a reglet, at least 1 inch deep into a mortar joint using an angle grinder. The top edge of the counter flashing is bent at an angle, inserted into the reglet, and the groove is sealed with polyurethane or tripolymer caulk. The metal then hangs down over the base or step flashing, overlapping by a minimum of 2 inches. On stepped chimneys or walls where the mortar joints are at varying heights, the counter flashing is cut in sections that follow the stair-step mortar joint pattern. Each section overlaps the one below it. On concrete or stone walls without mortar joints, a saw-cut reglet is used instead. Some manufacturers offer surface-mounted counter flashing systems that use adhesive and mechanical fasteners, but embedded reglet installations are the most reliable and code-standard method.

Common Counter Flashing Failures

The most common counter flashing failure is sealant deterioration at the reglet. Exposed to UV light, temperature swings, and moisture, even high-quality polyurethane sealant eventually shrinks and cracks, typically within 5 to 10 years. Once the sealant fails, water enters the reglet and runs behind the counter flashing, which then runs behind the base flashing and into the roof assembly. The second most common issue is counter flashing that was never properly embedded. Some roofers surface-mount counter flashing with a bead of sealant against the masonry face, which fails quickly because it relies entirely on adhesion rather than a mechanical lock. Corrosion at the bend point where the metal exits the mortar is another frequent problem, particularly with galvanized steel in areas with freeze-thaw cycles.

Counter Flashing and Insurance Claims

Counter flashing damage in insurance claims falls into two clear categories: storm damage and wear and tear. Wind can physically pull counter flashing out of a mortar joint if the reglet seal has weakened, and hail can dent or deform the hanging portion. These are covered perils. Sealant deterioration, mortar erosion, and corrosion are maintenance issues that insurance does not cover. The challenge for adjusters is that storm events often exploit pre-existing weaknesses. A wind event may displace counter flashing that already had compromised sealant. In these cases, the displacement itself is storm damage even if the underlying sealant was aging. Documentation should clearly show the displaced metal and the condition of the reglet. Xactimate line items for counter flashing include removal, reglet preparation, new material, and sealant, so each step should be scoped individually.