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Step flashing is one of the roofing details that looks straightforward on a manufacturer diagram and turns out to be far more consequential once a building is standing and water is moving across its surfaces. It is used wherever a sloped roof plane meets a vertical wall, such as along the sides of a dormer, at a chimney sidewall, or where an addition ties into an existing structure. Rather than a single continuous strip, step flashing is made up of individual L-shaped pieces, one installed with each course of shingles as the roofer works up the slope.
Each piece typically measures around five by seven inches, though sizes vary by manufacturer and local practice, and is bent at roughly a ninety degree angle so that one leg lies flat on the roof deck under the shingle course and the other leg runs up the wall behind the siding or stucco cladding. The horizontal leg is usually lapped by the shingle above it by about two inches, and the vertical leg is tucked behind the wall covering rather than caulked to its face, which allows any water that gets behind the cladding to drain back out over the roof surface instead of collecting at the seam. Common materials include galvanized steel, aluminum, and occasionally copper, chosen for corrosion resistance and compatibility with the adjacent cladding. Gauge and metal thickness can vary as well, with heavier gauge steel or aluminum generally holding its shape better under foot traffic during reroofing and resisting minor hail impact with less deformation than thinner stock.
The overlapping, shingle by shingle arrangement is what distinguishes step flashing from a single continuous piece of flashing metal, and it is also what allows the roof to move slightly with temperature changes without opening a gap at the wall. Each piece is nailed only through its roof leg, not through the wall leg, so the assembly can flex independently of the cladding above it as the building expands and contracts through a Minnesota winter and summer.
When this detail is examined during a roof inspection, the count of individual flashing pieces relative to the number of shingle courses is one of the more telling observations, since a mismatch can indicate that flashing was skipped, reused improperly, or covered without inspection. Physical condition matters as well: hail can dent exposed step flashing without necessarily perforating it, while long-term corrosion, loose fasteners, or gaps where the vertical leg has pulled away from the wall are separate issues tied to age and workmanship rather than to a specific storm event. Because the vertical leg is hidden behind siding or stucco, a full assessment sometimes requires removing a section of cladding, which is not always practical or agreed to during a claim inspection.
Whether existing step flashing should be reused when only the shingles are being replaced, or replaced along with the roofing material, is a question that depends on its physical condition, the type of cladding it sits behind, and the installation instructions published by the shingle manufacturer, several of which address flashing reuse directly. Industry references such as the National Roofing Contractors Association technical manuals and ASTM guidance on flashing materials provide a framework for evaluating condition, but the answer in any given case comes from what is found during inspection rather than from a general rule. An appraiser or umpire reviewing this detail is documenting observed condition and matching it to accepted construction practice, not making a coverage determination, which remains a matter for the policy language and the parties to the claim.
This article is general education about how the appraisal process commonly works. It is not legal advice, and specific procedures can vary by state and policy.
Russ Lis is a working property insurance appraiser and umpire based in Minnesota, serving clients nationwide. Contact Appraisal Resolution.