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Glossary

Vapor Retarder

A vapor retarder is a material that has a permeance of 1.0 perm or less and greater than 0.1 perm. A vapor retarder is vapor semi-impermeable and is classified as a Class II vapor control layer. The test procedure for classifying vapor retarders is ASTM E-96 Test Method A (the desiccant or dry cup method).

Related terms: Permeance, Vapor Control Layer, Vapor Semi-Impermeable

Related resource: IRC-FAQ: Insulating Sheathing Vapor Retarder Requirements; RR-0412: Insulations, Sheathings and Vapor RetardersInfo-312: Vapor Permeance of Some Building MaterialsInfo-500: Building Materials Property Table