Is a vapor open membrane needed below a ventilated attic?
I am building a passive house in NH climate zone 6A with thick EPS exterior insulation, where the WRB/Air barrier will be between the foam and the sheathing. The WRB will likely be a vapor closed peel and stick membrane. I have read that as long as the sheathing can dry to the interior of the home, I am safe.
The attic of the home will be a traditional ventilated attic with an 8 pitch roof and blown in cellulose insulation. This got me wondering is there any benefit to using a smart vapor open membrane such as Siga or pro clima between the drywall and the attic insulation for an air barrier? Or would less costly vapor closed options be just as fine?
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