Tag Archives: vapor diffusion

Is a Vapor Retarder Necessary in a Low-Slope Roof Assembly?

Green Building

Is a Vapor Retarder Necessary in a Low-Slope Roof Assembly?

Originally published on October 7, 2016 by BNP Media through the Building Enclosure Blog. . If you have designed or built a low-slope roof with a single-ply membrane, at some point you will be confronted with this simple question: Is the vapor retarder necessary? With considerable costs at stake, the prospect of omitting a vapor retarder is always a precarious notion and one that merits careful consideration of the project-specific dynamics at play. Consider the Entire Assembly In order to….

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The Difference Between Permeance and Permeability

Green Building

The Difference Between Permeance and Permeability

Originally published on April 18, 2016 by BNP Media through the Architectural Roofing & Waterproofing Blog. All information presented in imperial (I-P) units. Water vapor transmission is a rather confusing issue. The difference in vapor pressure between two sides of a building envelope assembly is the driving force behind vapor transmission. (Although by comparison, gaps in the envelope account for vastly greater amounts moisture migration due to vapor-laden air infiltration.) Vapor = Latent Heat; Air Temperature = Sensible Heat The….

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