Tag Archives: vapor diffusion

The Moisture Threat of Infiltration to the Building Envelope

Green Building

The Moisture Threat of Infiltration to the Building Envelope

Originally published on May 1, 2019 by BNP Media through the Building Enclosure Blog. The ways in which liquid and vapor move through our building envelopes are complex, and even today not completely understood; but the fact that lots of water can (and does) move through porous building materials is a phenomenon that rules over so much of the way we build. Two major modes of moisture travel – gravity and capillary action – are related to bulk water management, which is….

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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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