What is roof flashing?

Roof flashing is the thin metal or roll roofing that keeps water out of the places where a roof is interrupted. Flashing is pieces of metal or roll roofing placed around any intersection or projection in a roof, such as vent pipes, chimneys, adjoining walls, dormers and valleys, to keep water from seeping into the building. Shingles shed water across an open slope, but they cannot seal a joint, so flashing does that job.

Where flashing goes

Anywhere the roof meets something else, or something pokes through it:

• Chimneys. Flashing runs up the sides and across the back of the chimney, and the top edge is usually covered or tucked into the masonry.
• Walls and dormers. Where a roof slope runs into a vertical wall, flashing is lapped under the roof covering and up the wall.
• Valleys. The channel where two slopes meet carries a lot of water off the roof.
• Vent pipes. A plumbing vent boot is a small flashing with a collar around the pipe.
• Skylights. Skylight makers supply flashing kits matched to the roof type; VELUX describes its flashing systems as designed to shed water without relying on sealants that can break down over time.^[2]
• Eaves and rakes. Metal edging along the roof edge guides water off the roof and into the gutter.

What it is made of

Flashing is usually sheet metal, and roll roofing is also used in some details. Which material is right depends on the roof covering and the detail, which is one reason a roofer's quote should name it.

Why it matters

Flashing is where roofs often leak first. The USDA Forest Service says many apparent roof leaks are really flashing leaks.^[1] Without good tight flashings around chimneys, vents, skylights, and wall/roof junctions, water can leak into buildings and damage walls, ceilings, insulation, and even the electrical system.^[1] The same guide says flashings should be checked twice a year when the roof is inspected and the gutters are cleaned.^[1]

Common signs of a flashing problem are a stain on a ceiling or wall near a chimney, dormer or vent, rust or gaps along a metal edge, cracked or missing sealant, and water that only shows up in wind-driven rain. A smear of roofing cement over a joint is a temporary patch, not a repair, and it can hide the real failure.

Look from the ground

Binoculars from the yard show most visible damage, and photos taken from the ground help a roofer scope the job before a visit. Stay off the roof. OSHA's roofing guide says falls are the leading cause of death in the construction industry.^[3]

When to call a licensed pro

Flashing repair is roofwork, so it is a job for a roofer, not a ladder project. In Virginia the Board for Contractors defines roofing contracting as the service that provides for the installation, repair, removal, or improvement of materials common to the industry that form a watertight, weather resistant surface for roofs and decks.^[4] If the work is valued at $1,000 or more, a valid Virginia Contractor's License is required for the license category in which the contractor is to work.^[5] Check any roofer with DPOR's licence lookup before you pay a deposit.

On permits, the Uniform Statewide Building Code exempts replacement of an unlimited amount of roof covering in Group R-3, R-4, or R-5 buildings, provided the building is not in an area where the nominal design wind speed is greater than 100 miles per hour.^[6] Rules can differ for unusual work or properties, so ask your building department before you start.

Next, see how much flashing repair costs in Virginia and who repairs chimney and roof flashing. Browse all roofing answers or roofing businesses near you.

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