Duct Wrap / Liner Material Takeoff
External duct-wrap insulation area and rolls, where the overlap and corner compression add to the bare surface: perimeter = 2 x (width + height); wrap = perimeter x length x overlap/waste factor; rolls = ceil(wrap / roll coverage). A 20 x 12 in duct, 40 ft long, needs 245 sf of wrap (3 rolls of 100 sf); a larger 30 x 20 in duct needs 383 sf (4 rolls) - the perimeter, not the length, drives the wrap. The factor (~1.15) covers the taped overlap; internal liner is taken off on the interior perimeter.
Formula and source
perimeter_ft = 2 x (width_in + height_in) / 12; wrap_sf = perimeter_ft x length_ft x overlap_waste_factor; rolls = ceil(wrap_sf / roll_coverage_sf).
Duct-wrap takeoff identity by name (developed area x overlap/waste factor; rolls from wrap / coverage); first-principles takeoff arithmetic.
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