Best Crawl Space Vapor Barrier 2026 — 6 mil vs 10 mil vs 20 mil Reviewed

Frequently Asked Questions

What thickness vapor barrier do I need for a crawl space?

For most crawl spaces, 10–20 mil is the recommended thickness. 6-mil poly is the building code minimum in many areas but punctures easily during installation and foot traffic — any crawl space access or future work tears through it. 10 mil is the minimum most moisture control professionals recommend; 20 mil is the standard for full encapsulation projects. If you are installing a crawl space dehumidifier and sealing the vents (full conditioning), 20 mil minimum, preferably a Class A product like Americover or Stego Wrap.

Should I encapsulate my crawl space or just add a vapor barrier?

A vapor barrier covers only the ground (dirt floor). Crawl space encapsulation covers the ground AND the walls, seals all vents, and typically includes a dehumidifier and sump pump. Encapsulation is more expensive ($5,000–$15,000 professionally installed) but controls humidity more completely and can qualify the crawl space as conditioned space. A basic vapor barrier costs $500–$2,000 installed and controls ground moisture but not humid outside air entering through vents. If your crawl space humidity exceeds 70% regularly (especially in humid climates), encapsulation is typically worth the investment.