Single-Ply Membrane Roof Rolls and Seam Length
Rolls and seam length for a single-ply membrane (TPO/EPDM/PVC), where the side lap eats the usable width: usable = roll width - side lap; rolls = ceil(area x (1 + waste) / (usable x roll length)); seam = area / usable. An 8,000 sf roof on 10 ft x 100 ft rolls with a 6 in side lap takes 9 rolls and ~842 LF of seam; a wider 12 ft roll cuts it to 8 rolls and 696 LF - a wider sheet cuts both the rolls and the welding. Fasteners and cover tape are separate.
Formula and source
usable_w_ft = roll_width_ft - sidelap_in/12; rolls = ceil(roof_area_sf x (1 + waste_pct/100) / (usable_w_ft x roll_length_ft)); seam_lf = roof_area_sf / usable_w_ft.
Single-ply membrane takeoff identity by name (usable width nets the side lap; rolls from area / usable coverage; seam from area / usable width); first-principles takeoff arithmetic.
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