How Many Crawl Space Vapor Barrier Rolls Do You Need?
Find how much vapor barrier you need for crawl-space floors and walls, then see the whole rolls to buy after wall upturn, overlap, and waste.
Last updated: September 14, 2026
Use the direct area option for an irregular crawl-space floor.
Overlap defaults to 6″ and waste to 10% (change under Advanced).
Vapor Barrier Order Summary
600 sq ft floor · 12 in upturn · 10 × 100 ft — 1,000 sq ft · 6 in overlap · 10% waste
How we calculate
rolls = ceil(order area ÷ effective coverage per roll)
The roll label gives nominal coverage. A 6-inch overlap reduces usable width, then the waste allowance and whole-roll rounding are applied.
Worked examples
20 × 30 ft crawl space
12 in upturn · 10×100 roll · 6 in overlap · 10% waste
1 roll
The 600 sq ft floor plus 100 sq ft of wall upturn becomes 770 sq ft to order; each roll provides about 950 sq ft after overlap.
1,000 sq ft floor only
0 in upturn · 10×100 roll · 6 in overlap · 10% waste
2 rolls
The 1,100 sq ft order area is more than one roll's usable 950 sq ft coverage.