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.
Example
You enter
- Roof area (ft²) 8000
- Membrane roll width (ft) 10
- Membrane roll length (ft) 100
- Side lap (in) 6
- Waste allowance (percent) 5
You get
- Usable w (ft) 9.5
- Membrane rolls 9
- Seam (LF) 842.1
Details, formula, and sources
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.
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.
The membrane takeoff is public quantity geometry; the membrane and lap come from the manufacturer and the wind-uplift design.
Estimate. AHJ and licensed professional govern.
Field names used by the API: roof_area_sf, roll_width_ft, roll_length_ft, sidelap_in, waste_pct, usable_w_ft, rolls, seam_lf
- Usable width roll width minus the side lap (a 10 ft roll with a 6 in lap nets 9.5 ft)membrane manufacturer
- Side lap set by the manufacturer and the wind-uplift design (~6 in typical)manufacturer / uplift design