What Is Roof Flashing and Why Does It Matter?

What flashing does

Anywhere the roof surface is interrupted, by a chimney, a wall, a vent pipe or a valley where two slopes meet, there is a seam that water can get into. Flashing is thin metal, and sometimes rubber, installed to direct water away from those seams and back onto the shingles.

Common types of flashing

• Step flashing: L-shaped pieces woven in with the shingles where a roof meets a wall or chimney side.
• Counter flashing: covers the top of step flashing on chimneys, often set into the brick.
• Pipe boots: collars that seal around plumbing vents.
• Valley flashing: lines the valleys where two roof planes meet.
• Drip edge: metal along the roof edges that directs water into the gutter.

Signs flashing has failed

• Leaks or stains near a chimney, wall or vent
• Rust, bent or lifted metal
• Cracked sealant or a cracked rubber pipe boot
• Missing pieces after a storm

Repair or replace the flashing?

Sealant alone is a short-term fix. Lasting repairs usually mean replacing the flashing itself, and during a full roof replacement, flashing is normally replaced along with the shingles.