Interior walls using rough cut lumber and insulation?
matthewezra
| Posted in GBA Pro Help on
We are using a restored barn frame to build a home. Our thought was erect frame, then wrapping the frame with painted rough cut, then applying 15lb felt paper, then framing w/ 2×4 or 2×6. We would then insulate w/ fiberglass, apply OSB sheathing, house wrap and then the necessary R value of foil faced poly iso to conform w/ code, being careful to seal all joints. Is this a proper wall build up or is there a better way to do this?
Thank you for your time GBA pros have been very knowledgeable.
Matt
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Replies
Matt,
That's one way to do it, but there are better ways.
First of all, many people who want to add insulation to the exterior of an old barn (or a new post-and-beam timber-frame building) use SIPs. This method is fast, but not particularly cheap.
Your plan has a few weak points: not much of an interior air barrier (the felt paper isn't really an air barrier), and the use of fiberglass batts between your studs. Dense-packed cellulose would certainly be preferable to fiberglass batts.
There are so many ways to build walls, that it's hard to come up with a single method that is best. Whatever method you choose, pay attention to air sealing.
Matt,
One more point: if you are really interested in "a better way to do it," most experts would advise you that plywood sheathing is preferable to OSB sheathing (because OSB sheathing isn't very moisture-tolerant). Of course, plywood costs a little more.
Martin,
Thank you for the response. I have read many Q&A's and nothing seems to fit the situation. I can't install gypsum to the structure behind the rough cut. SIP's are out - have already been down that road. What would your suggestion be for air sealing behind the rough cut if we were to use stabilized cellulose in a 2x4 wall, plywood house wrap and then 1.5-2" of poly iso?
Matt,
To provide an interior air barrier, you could install plywood, OSB, plastic housewrap, MemBrain, or one of the European membranes sold by Small Planet Workshop or 475. Any of these products could be installed on the exterior side of the rough-cut boards. No matter what product you choose, don't forget to tape the seams.