What is the recommended perm rating for a class 1 vapor retarder?

The recommended perm rating for a class 1 vapor retarder is 0.1 perm. This rating indicates that the material has very low permeability to water vapor, effectively serving its purpose of limiting moisture movement through building assemblies. Class 1 vapor retarders, often referred to as "vapor barriers," are essential in controlling moisture in environments where condensation might occur, such as in walls or ceilings in cold climates. Their low perm rating is specifically designed to prevent moisture from passing through, thereby protecting the structural integrity of the building materials and preventing mold growth.

A vapor retarder with a perm rating of 0.1 has sufficient resistance to moisture transmission, making it ideal for use in applications where a significant difference in vapor pressure exists, such as in a warm, humid interior compared to a cold exterior. This distinction is crucial for maintaining an effective moisture control strategy in building design and construction.