What is a Class 2 vapor retarder?

Class II vapor retarders have a permeance level between 0.1 perm and 1 perm and are considered semi-impermeable. Examples include unfaced expanded polystyrene, fiber faced polyisocyanurate and asphalt-backed kraft paper facing on fiber glass batt insulation.Click to see full answer. Then, what is a class one vapor retarder?A Class I vapor retarder is a material with a permeance less than 0.1. That definition may be difficult to understand without some additional context. Permeance, for example, is the amount of moisture vapor that can pass from one side of an object (in this case a plastic liner/sheet) to the other.Also Know, what materials are in vapor retarders? Materials used as vapor retarders: Elastomeric coatings can provide a vapor barrier and water proofing with permeability ratings of . Aluminum foil, 0.05 US perm (2.9 SI perm). Paper-backed aluminum. Asphalt or coal tar pitch, typically hot-applied to concrete roof decks along with reinforcement felts. what does vapor retarder mean? A vapor retarder is defined as a material or system that adequately retards the transmission of water vapor under specific conditions. A vapor retarder helps prevent water vapor from moving into building assemblies, like walls, where it can condense into liquid water within the structure.What is the difference between vapor barrier and vapor retarder?The definition of the differences is illustrated by the Building Science Corporation — a vapor barrier is defined as a layer with a permeance rating of 0.1 perm or less. A vapor retarder is defined as a layer with a permeance greater than 0.1 perm but less than or equal to 1 perm.

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