Step Flashing vs Continuous Flashing on Roof-to-Wall Transitions
Where a sloped shingle roof meets a vertical sidewall, installing one long continuous piece of L-shaped flashing is an amateur shortcut that will eventually leak.
A continuous metal strip cannot expand and contract with seasonal temperatures without buckling, and any water penetrating one section runs down the entire length of the wall. Professional roofers install step flashing: individual, overlapping 4"x4" or 5"x5" L-shaped metal pieces woven into each course of shingles.
The Correct Step Flashing Assembly
Proper installation requires strict adherence to fastener and dimension rules:
- Dimensions: Each piece must be at least 7 to 8 inches long and 8 inches wide (bent to 4" vertical by 4" horizontal) under NCRC Section R905.2.8.3.
- Fastening Rule: Step flashing pieces must be nailed only high up on the horizontal deck flange. They must NEVER be nailed into the vertical wall framing; differential movement between roof and wall will shear or tear the metal.
- Counter-Flashing on Masonry: When abutting brick or stone, a reglet groove is diamond-sawn into the mortar joint, and counter-flashing inserted, mechanically wedged, and sealed with polyurethane sealant (MasterSeal NP1 or SikaFlex).
Code and Association References
2018/2024 North Carolina Residential Code, Section R905.2.8.3 (Sidewall Flashing)
NRCA Roofing Manual: Steep-Slope Roof Systems (Detail R-07)
SMACNA Architectural Sheet Metal Manual (Counter-Flashing Details)
Related service: Roofing Contractor · More in Roofing & Storm Damage
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