Drip Edge and Flashing, Explained

Drip edge is a metal flashing installed along the edges of a roof — the eaves and rakes — that directs water away from the fascia board and into the gutter rather than letting it run down behind the gutter or drip onto the fascia directly. Without it, water tends to wick back under the shingle edge or run down the fascia, contributing to rot over time.

Flashing is thin metal installed anywhere two roof surfaces meet, or where the roof meets a vertical wall, chimney, or penetration like a vent pipe or skylight. Its job is to redirect water around these transition points, which are inherently more vulnerable to leaks than the flat, uninterrupted field of a roof.

Where a roof meets a wall or chimney, individual pieces of step flashing are woven into each course of shingles as they're installed, layering water down and away in stages rather than relying on a single continuous piece. Done correctly, this is one of the more labor-intensive but important details in the whole roofing system.

Valleys, where two roof slopes meet at an internal angle, concentrate a significant amount of water runoff into a single channel. Valley flashing is designed to handle that concentrated flow, and it's an area worth checking specifically during any roof inspection, since valleys see more water volume than almost anywhere else on the roof.

Shingles are designed to shed water across a continuous, uninterrupted surface. Every place that continuity breaks — a chimney, a wall, a valley, a vent pipe — depends on flashing instead, and flashing installed poorly, or reused during a roof-over instead of replaced, is one of the most common sources of leaks on an otherwise sound-looking roof. It's also one of the details easiest for an inspector to check and hardest for an untrained eye to properly evaluate from the ground.

Round or square boots wrap around vent pipes to seal that penetration, and skylights use their own manufacturer-specific flashing kits designed to integrate with the surrounding shingles. Both are common trouble spots as the rubber or sealant components age and lose flexibility over the years, well before the surrounding shingles show any comparable wear, which is why these specific points are worth checking on their own during an inspection.

Rust streaking below a metal flashing joint, visible gaps where flashing has pulled away from a wall or chimney, and cracked or shrunken sealant around a penetration are all signs worth flagging during an inspection, even without an active leak yet. Flashing failure is often gradual, which means there's usually a window to address it as a repair before it becomes a more significant interior water problem.

Caulking over an old flashing joint can buy a little time, but it isn't a substitute for properly integrated, replaced flashing during a full roof replacement. Sealant degrades faster than metal flashing does, and relying on it as the primary water barrier at a vulnerable detail like a chimney or valley is one of the more common shortcuts that leads to a callback within a year or two.

It's a reasonable question to ask directly: will flashing at every chimney, wall and valley be fully replaced during the project, or reused and just resealed. A contractor doing the job properly should have a clear, specific answer, and the difference between the two approaches is one of the more common places corners get cut without it being obvious in the finished appearance of the roof.