Vapor Barrier Calculator — ft, rolls, cost
How to use this calculator
Select application — crawlspace floor, wall interior, under-slab, or custom area. Choose membrane thickness (6-20 mil) and roll size. Set overlap (6-12″) and waste allowance. Results update instantly.
Seam tape — vapor barrier tape 2″ wide, ~180 ft per roll, for all overlapping seams.
Fasteners — T50 staples for wall applications (~1 per 12″ along seams), acoustic sealant for perimeter.
Cost — per roll of membrane, tape, staples/sealant.
Saved Calculations
| Time | Application | Area ft² | Rolls | Cost |
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How to Calculate Vapor Barrier
Measure the area to cover — crawlspace floor, wall interior, or under-slab. For crawlspaces, add wall run-up height to account for membrane running up foundation walls. Apply seam overlap (6″ for floors, 12″ for walls) and waste allowance.
Formulas
Base area = length × width. Crawlspace: total = floor area + perimeter × run-up height. Overlap factor = 1 + (overlap / roll width). Adjusted area = base × overlap factor × (1 + waste%). Rolls = adjusted area / roll coverage.
Membrane Thickness Guide
6 mil — standard for most crawlspaces and under-slab (ASTM E1745 Class C). 10 mil — heavy-duty for high-traffic crawlspaces (Class B). 15 mil — premium, puncture-resistant (Class A). 20 mil — commercial grade, reinforced.
FAQ
How much overlap? Minimum 6″ for floor applications, 12″ for wall seams per IRC R506.2.3. Do I tape the seams? Yes — all seams must be taped with approved vapor barrier tape. Do I need sealant? Apply acoustic sealant at all perimeter edges where membrane meets foundation walls, piers, or other penetrations.
