Smart Vapor Barrier
Jeff_Garnelis
| Posted in General Questions on
Hi GBA Community,
I understand using a directional vapor barrier on exterior walls, especially when there is exterior foam restricting the stud bay from drying to the outside. My question is do I need the directional vapor barrier on my ceiling or would it be more cost effective to just use poly. Above the ceiling will be R60 blown in cellulose and a vented attic. The roof will be sheathed and taped with Zip products. Thank you in advance.
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Replies
Jeff, what climate zone are you in?
You may not need a vapor retarder (besides painted drywall) at all.
Do you use AC?
I am in Zone 5. I live in Connecticut so some parts of the year I will be using AC.
Jeff,
There is no such thing as a "directional vapor barrier." A vapor retarder or vapor barrier is symmetrical. It works (or doesn't work, as the case may be) both ways.
Hi Martin,
I pulled this off Siga's website. "Majrex 200 varies depending on the direction of vapor flow, making it currently the only directional smart vapor control membrane on the market."
Maybe I am misunderstanding your response. Can you please clarify? Thank you in advance.
Jeff,
I need to study up on Majrex 200. It appears I'm wrong -- although I would like to confirm that with more personal research. In the meantime, I apologize for my misleading advice.