Thermal bridging – Cold climate
I am building a cabin and am concerned with thermal efficiency in my envelope. I know this topic has been disclosed in depth but I was unable to find the right answer..
So, I am contemplating three wall assemblies. What you your opinions? Option C probably costs the most…
[Option A – Exterior Rigid Insulation]
Plywood good one side interior finish
6 mil Polyethylene Vapour barrier
2×6 studs @ 24 inch o/c
RSI 3.52 (r-20) Batt insulation…perhaps cellulose insulation
Rigid insulation c/w spunbonded olefin facer (mb)
Galvanized Anchors secured to studs (to support custom metal siding panels)
3/4″ air gap
3/4″ Exterior grade plywood with custom metal siding
[Option B – Interior Rigid Insulation]
Plywood good one side interior finish
6 mil Polyethylene Vapour barrier
Rigid insulation
2×6 studs @ 24 inch o/c
RSI 3.52 (r-20) Batt insulation…perhaps cellulose insulation
3/4″ Exterior grade plywood sheathing
2 layers of 30 min building paper (mb)
3/4″ Air space (vertical P.T. strapping)
3/4″ Exterior grade plywood with custom metal siding
[Option C – Staggered Stud]
Plywood good one side interior finish
6 mil Polyethylene Vapour barrier
2×6 staggered stud wall @ 24 inch o/c
RSI 3.52 (r-20) Batt insulation…perhaps cellulose insulation
3/4″ Exterior grade plywood sheathing
2 layers of 30 min building paper (mb)
3/4″ Air space (vertical P.T. strapping)
3/4″ Exterior grade plywood with custom metal siding
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Replies
David: First, I am an amateur. Post where you are; it is important. From your spelling of "vapour", I suspect Canada, and 6 mil poly is not required there, though may be OK. ("Not required" according to a Canadian on another forum. If you can demonstrate you'll stop vapor by other means, those means are acceptable. Check w/ you local inspector.) Were I you, I'd look here and google double stud wall, Larson Truss, Riversong Truss, The Sunrise House, and dense packed cellulose. If you decide to use batt insulation, look for rock wool, wool, or cotton, IMO; fiberglass is last on the list. For my location, a double stud 2x4 wall with dense packed cellulose was the cheapest per R value of several alternatives, and is not terribly complex to build. There are lots of resources discussing that option and many people willing to help. It is also one of the greenest options. Study air sealing, too; very important. Why the second layer of 3/4" ply, and are you certain 3/4" is necessary for your area?
I would rather build from inside to out: ½” drywall, 2x6 @24” O.C. wall, cellulose, ½ Plwd, WRB, 2”-4” taped rigid foam (depends on your location), vertical strapping, Siding.
David,
I agree with John -- don't install any interior polyethylene, especially if your wall assembly includes any exterior rigid foam.
Exterior rigid foam makes much more sense than interior rigid foam, because exterior rigid foam does a better job of insulating rim joists and partition intersections.