Field glossary

Vapor retarder

A layer that slows water vapor diffusion through the assembly, rated by perm; a vapor barrier is the lowest-perm version, Class I at 0.1 perm or less

Used across 5 Anvilfield field guides, most in Roofing.

Also defined as

Concrete: ASTM E1745 plastic sheet under the slab that blocks ground moisture from reaching the floor finish
Concrete: Sheet under the slab that blocks ground moisture but seals the bottom and can worsen curling

Where this shows up