Under-Slab Vapor Barrier Rolls and Seam Tape
Poly vapor-barrier rolls for a slab (with lap and waste) and the seam tape: rolls = ceil(area x (1 + overlap + waste) / roll coverage); seam tape = area / roll width. A 3,000 sf slab on 10-mil 1,000 sf rolls with 6 in laps and waste takes 4 rolls and about 300 LF of tape; a 6,000 sf slab takes 7 rolls and 600 LF. Under-slab retarders follow ASTM E1745 (a Class A membrane is common under conditioned slabs); penetrations and the perimeter seal are added separately.
Formula and source
rolls = ceil(area_sf x (1 + overlap_waste_pct/100) / roll_coverage_sf); seam_tape_lf = area_sf / roll_width_ft.
Roll-takeoff identity by name (rolls from area over coverage with lap and waste; seam tape one seam per roll width); first-principles arithmetic.
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