Adding a room onto back of woodshed. Need info on vapor barrier.
-Montana. High eighties temp in summer. Forty below zero in winter. The room will be heated in the winter.
-2X6 walls and rafters (serving also as ceiling joists).
-metal roofing is already installed over the rafters on 1X4 purlins 24 inches on center. So can’t put hard insulation in top of purlins.
-plan to use fiberglass insulation
-will it work to have the kraft faced paper on the insulation batts facing the interior of the room in both the walls and ceiling as a vapor barrier?
Replies
Yes, but...
Plain Kraft paper isn't really a vapor barrier unless the product incorporates something like tar or aluminum foil. Any of the faced fiberglass products are supposed to have the facing installed towards the living space.
Go one better & use 6 mil polyethylene sheeting over the installed product, then tape seams before installing wall finish material. If it's gonna be a non-living space w/ no wall finish (drywall, etc.) any vapor barrier likely won't last long.
Yeah, you want the vapor barrier on the inside. And using a separate poly barrier vs just the kraft does double duty since it will greatly reduce air infiltration.