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Vapor Barrier Calculator

Estimate how many rolls of 6-mil poly vapor barrier you need for a crawlspace or basement.

Computed in your browser — nothing you enter is uploaded. Figures are presented for United States against IRC 2024, and every formula is cited under regulatory standards below.

Last verified 2026-08-25 · v1.0.0

Market
Imperial · sales tax

Vapor barrier rolls needed

2 rolls

High confidence
Area to cover (with overlap allowance)
1184.03 sq ft

Running these inputs gives 2 as the vapor barrier rolls needed. Note that floor or wall area sits at the low end of the range this calculator was checked against, so treat the output as indicative rather than settled. Currently reading for United States under IRC 2024 — pick a different market above and the figures re-cast accordingly.

Estimated cost — your price

This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.

Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — confirmed fixes become pinned regression tests.

[Schema Verified] Computed in alignment with American Concrete Institute (ACI 318-19) formulas and International Residential Code (IRC 2024) spatial boundaries.

Regulatory standards & verification citations

  • A standard 6-mil poly vapor barrier roll (10 ft x 100 ft) covers approximately 1,000 sq ft

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Most jobs need more than one number. Add the calculators you need next and they open right here, underneath this one — your figures stay on screen and nothing is lost to a page change.

Frequently asked questions

Why does a crawlspace need a vapor barrier at all?
Bare soil constantly releases moisture into the crawlspace air, which can lead to wood rot, mold, and higher humidity in the living space above — a vapor barrier blocks that moisture at the source.
Do seams need to overlap?
Yes — seams are typically overlapped at least 6-12 in and often taped, which is what the 10% waste allowance in this estimate accounts for.
Is 6-mil poly the standard thickness?
6-mil is a common standard for crawlspace vapor barriers, though some installers use heavier 10-20 mil reinforced barriers for better puncture resistance in high-traffic crawlspaces — coverage area math is the same regardless of thickness.