PDD Vapor Barrier Location

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    Scott Barber

    For the exams, you'll always be given a location. There's no universal standards for these types of details that depend on the location, I wouldn't think.

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    Tyler Dallison

    The Vapor Barrier VB is to be on the warm side of insulation. In the first example image, Cold climates the VB goes behind the interior Gypsum and on the interior side of the batt insulation.  In the second example image, Warm climates the VB goes on the exterior sheathing. Think of how a cold glass of water condensates on the exterior on a warm summer day (this is a Warm climate and thus you need a moisture vapor barrier to mitigate water moving thru the assembly.) Images taken from buildingscience.com

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    Scott Barber

    Since only extreme climates are 'always' hot or cold, most climates are going to experience both hot and cold weather (I'm assuming that's what you mean by "mixed climates"?). You need to place the vapor barrier on the predominantly warm side. I don't remember any questions that were vague about the climate they were asking about, it should be pretty clear if it's a predominantly warm or predominantly cold climate. 

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    Claire Cornett

    In the second example from the building science diagram, in the event there was no batt insulation, would the vapor barrier go outside of the rigid insulation in a warm climate? 

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    Matthew Dirksen

    According to figure 5, it would be in the same place. Of course regarding the wide spread miss-use of VBL's, I sure hope any questions regarding employing them are very clear. 

     

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