Psychrometric Saturday: Vapor Barriers

Vapor barriers stop, or at least greatly reduce the amount of water vapor from getting inside a building. This results in lower indoor dewpoint.
#airconditioning #heating #homeperformance #hvactraining #betterhvac #bluecollar #buildingscience #comfort #hvactech #hvac #psychrometrics

[@BenBogie-ee2sm]

Hey, Tim. The location in your illustration is commonly the location of the weather resistive barrier "WRB." Some WRB systems are vapor barrier but the majority are not. Vapor barriers, as far as building codes are concerned are generally located on the "warm in winter side" of an assembly. So, commonly the interior, directly behind the drywall.

[@timdestasiohvac]

@@BenBogie-ee2sm yes I mispoke since i have a zip system which does both. But even house wrap has a dual purpose as a wrb and a vapor retarder (not barrier), correct?
And yes in cold climates, the vapor barriers on the inside of the cavity.

[@BenBogie-ee2sm]

@@timdestasiohvac zip system is still only a vapor retarder (1-3perm), not a barrier. House wraps aren't usually used for vapor control; that's typically done by an interior control layer like 6mil poly or a variable membrane. Most often, they should be as minimally vapor restrictive as possible to prevent moisture from trapping in the building assembly and letting it dry to the outside. There are certainly caveats to that, but overall, that is the most common approach.
I totally enjoy your content BTW!

[@timdestasiohvac]

@@BenBogie-ee2sm thank you. I believe zip makes a pretty good vapor retarder though. And an effective air barrier.