Under-Slab Vapor Barrier Rolls and Seam Tape
Poly vapor-barrier rolls for a slab (with lap and waste) and the seam tape.
Example
You enter
- Slab area (ft²) 3000
- Coverage per roll (ft²) 1000
- Overlap + waste (%) 10
- Roll width (ft) 10
You get
- Vapor barrier rolls 4
- Seam tape (upper bound) 300
No published worked example is on file for this calculation. It is checked against a hand-worked derivation of its method and an independent reference test.
Details, formula, and sources
Scoperolls = 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 or tablerolls = ceil(area_sf x (1 + overlap_waste_pct/100) / roll_coverage_sf); seam_tape_lf = area_sf / roll_width_ft.
Source and editionRoll-takeoff identity by name (rolls from area over coverage with lap and waste; seam tape bounded by the total run, area / roll width); first-principles arithmetic.
Free accessThe roll-takeoff arithmetic is public quantity-survey math; the vapor-retarder class follows ASTM E1745 and the design.
What governsEstimate. AHJ and licensed professional govern.
API field namesarea_sf, roll_coverage_sf, overlap_waste_pct, roll_width_ft, rolls, seam_tape_lf
- Vapor-retarder class ASTM E1745 Class A common under conditioned slabs; the design and AHJ governASTM E1745
- Seam tape one taped seam per roll width; penetrations and perimeter seal separateinstallation practice