![]() ![]() Impermeable (≤1 US perm, or ≤57 SI perm) – such as asphalt-backed kraft paper, elastomeric coating, vapor-retarding paint, oil-based paints, vinyl wall coverings, extruded polystyrene, plywood, OSB.Vapor-retarding materials are generally categorized as: American building codes have classified vapor retarders as having a water vapor permeance of 1 perm or less when tested in accordance with the ASTM E96 desiccant, or dry cup method. inch of mercury ≈ 57 SI perm = 57 ng/s.Permeability can be reported in perms, a measure of the rate of transfer of water vapor through a material (1.0 US perm = 1.0 grain/square-foot Materials have a moisture vapor transmission rate ( MVTR) that is established by standard test methods. Technically, many of these materials are only vapor retarders as they have varying degrees of permeability. In this manner, the vapor barrier (in this case made of foil/ scrim/ kraft paper, called ASJ, all-service jacket, aluminium on the inside, white paper on the outside) can remain intact as it penetrates the fire barrier.Ī vapor barrier (or vapour barrier) is any material used for damp proofing, typically a plastic or foil sheet, that resists diffusion of moisture through the wall, floor, ceiling, or roof assemblies of buildings and of packaging to prevent interstitial condensation. Glass wool pipe insulation covering a steel pipe as it penetrates a mock-up concrete slab whose opening will be firestopped. ![]()
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