Skylight Flashing

What Is Skylight Flashing

Skylight flashing is a multi-piece assembly that seals the junction between a roof-mounted skylight and the surrounding shingles or roofing material. A standard skylight flashing kit includes four main components: sill (apron) flashing across the bottom of the skylight, step flashing up both sides, and head flashing across the top. Corner transition pieces connect the sill to the sides and the sides to the head. Most major skylight manufacturers (VELUX, Fakro, Wasco, and others) produce model-specific flashing kits engineered to integrate with their skylight frames. These kits include pre-formed pieces that fit the exact frame dimensions and incorporate drainage channels for condensation management. Using the manufacturer kit is critical for proper function and warranty coverage.

Installation Sequence

Skylight flashing installation follows the same bottom-to-top water-shedding logic as all roof flashing. The roof opening is prepared with ice and water shield membrane around the full perimeter, extending at least 6 inches past the rough opening on all sides. The skylight is set in the opening and secured to the framing. The sill (bottom) flashing is installed first, positioned under the downslope shingles so water flowing down the roof passes over the sill flashing and onto the shingles below without entering the opening. Step flashing pieces are then woven into the shingle courses up both sides of the skylight, exactly as they would be at a sidewall. The head flashing is installed last, tucked under the shingles above the skylight. Each component overlaps the one below it in the water-shedding sequence. The manufacturer kit typically includes interlocking corner pieces that connect sill to side and side to head without relying on sealant alone.

Common Skylight Flashing Problems

The most common skylight flashing failure is sealant degradation between the flashing and the skylight frame. This sealant is exposed to constant UV radiation and thermal cycling, causing it to crack and separate over 10 to 15 years. The second most common problem is using generic flashing instead of the manufacturer-specific kit. Generic pieces may not fit the frame profile correctly, may block the built-in condensation drainage channels, and will void the skylight warranty. Missing or undersized crickets behind wider skylights (typically 30 inches or wider) allow water and debris to accumulate at the upslope edge of the skylight, creating a pooling condition that overwhelms the head flashing. Improper sill flashing installation (base on top of downslope shingles instead of under them) directs water under the shingles at the lowest point of the skylight, which is the highest-volume water path.

Skylight Flashing and Insurance Claims

Skylight flashing claims require precise documentation of which components are damaged and how the damage occurred. Wind can lift head flashing or step flashing along the skylight sides, creating an entry point for water. Hail can dent or puncture the thin aluminum flashing pieces in most manufacturer kits. Fallen branches or debris can damage both the flashing and the skylight glazing. All of these are covered perils. However, gradual sealant deterioration between the frame and flashing is not storm damage and is excluded as wear and tear. When documenting skylight flashing damage, note the skylight manufacturer, model number (usually on a label inside the frame), and the specific flashing components that are damaged. Xactimate estimates should include the full manufacturer flashing kit rather than individual generic flashing pieces, since the kit components are designed to work as an integrated system.