Vapor Barrier Calculator
Calculates 6-mil, 10-mil, or 20-mil virgin polyethylene vapor retarder sheeting rolls for crawlspace encapsulation, concrete slab underlayment, and exterior wall moisture barriers with 12-inch seam overlaps.
Formula
Total Area with Overlap = Area × (1 + Overlap %); Rolls = Ceil(Total Area ÷ 1000)
1. Total Square Feet with 12" Overlap = Footprint Area × (1 + Waste %) 2. Poly Sheeting Rolls (10 ft × 100 ft = 1,000 sq ft) = Ceil(Total Area ÷ 1000) 3. Waterproof Seam Sealing Tape Rolls (180-ft roll) = Ceil(Total Area ÷ 350 sq ft/roll)
Inputs
- Crawlspace / Wall / Slab Footprint
- Polyethylene Thickness & Application
Worked example
Laying 10-mil heavy-duty virgin poly over a 1,200 sq ft crawlspace floor with 12" taped overlaps.
Outcome: Total plastic needed is 1,380 sq ft with 12" seam overlaps and wall turn-ups. Dividing by 1,000 sq ft/roll equals 1.38 rolls, rounding up to 2 full rolls of 10-mil poly (2,000 sq ft total). Seam tape: 4 rolls of heavy butyl vapor tape.
Why shouldn't you use regular silver duct tape on crawlspace vapor barriers?
Standard rubber-adhesive duct tape breaks down, dries out, and falls off within 6 to 12 months under high crawlspace humidity. Only use specialized vapor barrier tape coated with heavy-tack polyacrylic or butyl adhesive.