Roof Step-Flashing Piece Count

The step-flashing pieces for a roof-to-wall or chimney sidewall.

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Example

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No published worked example is on file for this calculation. It is checked against a hand-worked derivation of its method and an independent reference test.

Details, formula, and sources

ScopeOne piece is woven into EACH shingle course as the roof rises along the wall, plus one to start, so pieces = ceil(sloped wall run x 12 / shingle exposure) + 1. A 20 ft run against a wall at a 5 in exposure takes ceil(240/5) + 1 = 49 pieces; a longer exposure means fewer courses and fewer pieces. Order a few extra for waste. Each L-shaped piece laps the one below by the exposure and tucks under the siding/counterflashing -- step flashing is woven course-by-course, NOT a single continuous strip (a leak-prone mistake). A takeoff estimate; the shingle exposure, the flashing size, and IRC R905.2.8.3 and the manufacturer's details govern the install.

Formula or tablestep_flashing_pieces = ceil(wall_run_ft x 12 / shingle_exposure_in) + 1; order_pieces = ceil(step_flashing_pieces x (1 + waste_pct/100)).

Source and editionRoof step-flashing piece-count takeoff (one piece per shingle course) by name; IRC R905.2.8.3 and the shingle / flashing manufacturer's details govern the install.

Free accessThe piece count is public first-principles (one flashing per course plus one); the sloped wall run and the shingle exposure are the field measurements.

What governsEstimate. AHJ and licensed professional govern.

API field nameswall_run_ft, shingle_exposure_in, waste_pct, step_flashing_pieces, order_pieces

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