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Building Science FAQ — Ep. 4

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Air Barrier vs. Vapor Retarder

Welcome to Episode 4 of The Building Science FAQ series.

The Building Science FAQ video series explores some of the technical questions that crop up when specifying a low-slope roof.

In this episode, Jennifer Keegan, director of building and roof science, GAF, and Jim Kirby, GAF building and roofing science architect, address a common area of confusion: “What is the difference between an air barrier and a vapor retarder?” While an air barrier stops air leakage, a vapor retarder reduces moisture diffusion to reduce the risk of condensation forming in the roof assembly. But can an air barrier be a vapor retarder?


Episode 1: How Strong is a Thermoplastic Weld? 

Episode 2: How Chemical Resistant are TPO and PVC?

Episode 3: What is a roof coating?

Episode 5: What is the difference between a metal roof and a metal deck?

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