Roof Step-Flashing Piece Count
The step-flashing pieces for a roof-to-wall or chimney sidewall: one 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 and source
step_flashing_pieces = ceil(wall_run_ft x 12 / shingle_exposure_in) + 1; order_pieces = ceil(step_flashing_pieces x (1 + waste_pct/100)).
Roof 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.
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