The question “do I need a vapor barrier?” is flawed from the start.
When this question is asked, there are a few possible interpretations. One is that the questioner wants to know if they need polyethylene sheeting in their assembly. Polyethylene sheeting is conversationally referred to as a “vapor barrier.” The second possibility is that the questioner doesn’t understand that “vapor barrier” is not a technical term, that their assembly may need some sort of “vapor retarder,” and that in the building codes even polyethylene sheeting is considered a “vapor retarder”— a class I vapor retarder, to be specific. But even if they did ask the question right—does my assembly need a class I vapor retarder?—the answer from building scientists is no, probably not. Unfortunately, building inspectors often disagree.
And so, vapor control is the topic of this episode of The BS* + Beer Show. Our panelists are Doug Horgan and Christine Williamson. Doug is a highly credentialed builder, speaker, author, educator, and vice president of best practices at BOWA. Christine is a building scientist, educator, and creator of @buildingsciencefightclub on Instagram. After Doug presents a few case studies of building failures that resulted from inadequate vapor control, Christine makes a case for mostly vapor-open assemblies, and we take questions from attendees. Enjoy.
The next show is Thursday, June 19, from 6 to 7:30 pm: A deep dive into dehumidification. Our panelists are Nikki Krueger and Kristof Irwin.
Nikki is the Industry Manager for Therma-Stor’s residential moisture control products (including Ultra-Aire whole house ventilating dehumidifiers and Santa Fe freestanding dehumidifiers); a RESNET certified home energy rater; she sits on the RESNET SDC 200 and the NGBS TG-3 consensus committees; and is a board member of the Maryland Building Performance Association and a member of the ACCA Manual Low Load Homes (LLH) Advisory Committee.
Kristof Irwin, P.E., M Eng., is the principal of Positive Energy. Kristof’s background includes 12 years of experience as a custom builder (including deep energy retrofits and zero-net energy projects) and 11 years as a building science consultant. He worked for 14 years as an engineer, research scientist, and physicist for government and university research labs. And he is the host of the Building Science podcast.
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-You can reach Brian Pontolilo at [email protected]