Posted By Lbear on 23 Nov 2013 03:01 PM
Looking to get a whole wall R-Value for the following setup (commercial application):
- 10" I-studs with 3/8" OSB web (does this reduce thermal bridging?)
- 16" o.c. framing
- Icynene foam insulation under the exterior siding
What would the total whole wall R-Value be for this setup? Any STC ratings on this wall system?
The option is between the above or utilizing an ICF wall (2.5" EPS x 8" concrete x 2.5" EPS).
It's impossible to calculate the whole-wall R without the known framing fraction, which requires knowledge of the top/bottom plate descriptions, the window & door header/framing details, etc. The true dimensional depth of the TJI, and the thickness/breadth of the flanges would have to be specified too. (Is it a 9.5" nominal 2x10 replacement, or is it truly 10.00".)
Sheathing type and siding also factor in.
OSB runs about R1/inch of thickness, so a 3/8"web would be substanially less, about 1/4 that of a standard milled 2x10 with 12/8" thickness.
Just for yuks, say with all of the headers & framing & webbing add up to a 12% framing fraction (could be more, maybe slightly less) and it's 9.5", just like a 2x10, with OSB sheathing and fiber cement siding, half-inch gypsum on the interior. That would give you a whole-wall R in the R27-29 range, about 2x that of a 2x6 wall with half-pound Icynene cavity fill. The center-cavity R would be in the mid-30s. In most climates it would have comparable or slightly better thermal performance than a 2.5" +2.5" EPS ICF, but in high-altitude or hot-dry clear-air climates with very high diurnal temperature swings the ICF could beat it.
I doubt anybody has tested the soundproofing of that assembly. Foam is fairly mechanically rigid, and couples the interior wallboard to the exterior sheathing, and isn't generally as good a sound-reducer as a mass wall or a fiber-insulated wall.