Vapor barrier?
5grams
| Posted in General Questions on
Good Morning,
We have a new addition with OSB sheathed exterior covered with housewrap and board & batten vinyl siding. The interior side of exterior walls have R-21 kraft faced batts installed. We will be installing 1/2″ pine shiplap siding to interior walls (no drywall under it). My question is do we use vapor barrier or retarder under shiplap? Our plan was to use 6 mil plastic sheeting under the shiplap. We are zone 5 (mid-Michigan) and home is both heated and cooled.
Thank you,
Katie
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Replies
Don't use polyethylene plastic sheeting. Do focus on creating a good interior side air barrier and then have it tested with a blower door.
Kraft Faced batts meet code requirements.
I would use 1/2" drywall on the room side, then the pine boards. You can use the Airtight Drywall Approach (ADA) and get a good air barrier. Adding the drywall does also provide a fire break layer.
Katie,
Your suggested approach is associated with lots of problems, including moisture accumulation in the wall assembly and mold, because your wall lacks an interior air barrier. Interior air is likely to leak through the cracks of you shiplap pine boards.
Building codes do not require an interior vapor barrier in your climate zone -- only a vapor retarder, which is a less stringent barrier. As Z Design noted, the kraft facing meets code requirements for a vapor retarder.
You absolutely need an interior air barrier, however. Follow Doug's advice: Install interior drywall with taped seams, and test the effectiveness of your interior air barrier with a blower door before installing the boards.
Thank you for the feedback!