16 inch or 24 inch framing using 2 by 6
bobhol
| Posted in General Questions on
My contractor feels more comfortable building with 16 inch centers rather than using advanced framing methods.He claims the house will be stronger …when I made the point of more insulation area between studs ,his answer was because of the outside foam panels there was no difference with thermal transfer as the studs were now insulated….any thoughts
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Bob,
Some types of siding need to be nailed to the studs, not to the sheathing. And some types of siding need to be nailed every 16 inches, not every 24 inches. So it's important to check the fastening requirements for your chosen siding before choosing your stud spacing.
If all of your wall insulation is on the exterior side of the studs -- in other words, if you have a PERSIST wall -- then there is no thermal penalty accompanying 16-inch-on-center stud spacing. However, if you have some of your insulation between your studs, and some of your insulation on the exterior side of your studs, than there will be a thermal penalty to closer stud spacing. How much? "It depends."
More information here: The Pros and Cons of Advanced Framing.
The builder feels comfortable using Roxul between the 2 by 6 and 2 inches of foam on the exterior...although my original thoughts were for 4 inches on the exterior ...I am in Peterborough Ontario and I plan to heat with mini splits so Insulation is a must !!!
The builder isn't correct that there's "no difference" between 16" and 24" centers because of the foam, but it is true that it's less of a factor because of the foam. The type of siding installation matters, as Martin says. We are building an exterior foam project right now, and I grudgingly agreed to go with 16" centers because of uncertainty about fastening issues. We are using horizontal 1x4 strapping across the outside of the foam, and vertical siding. I need to make sure the strapping is held flat to the foam, so that there aren't waves in the siding. Depending on how this goes, I may move to 24" centers next time.
In Peterborough's climate with only 2" of foam on the exterior of 2 x 6 with high-density rock wool in the studs you'd wouldn't have sufficient exterior R to be protective of the sheathing without class-II or stronger vapor retarders.
If you went with 2x4 16" o.c. construction and 4" of foam you'd be in GREAT shape from a dew-point control at the sheathing point of view, and would have a higher performing (yet thinner) wall to boot.
Assuming 2" of R5.5/inch (derated for cold temp) polyiso a 2x6 24" o.c. wall with R23 rock wool, at a 20% framing fraction would deliver a whole-wall R of about ~R2-R28, allowing R1 for the siding/sheathing gypsum.
Assuming 4" of R5.5 foam on a 2x4 16" o.c. wall with R15s and a 25% framing fraction(due to the tighter spacing and doubled-up top plate) you'd be at R32 for whole-wall R, and with almost 2/3 the center-cavity R located the exterior to the sheathing, there is absolutely no need for interior vapor barriers.
The Fujitsu AOU15RLS2-H (the "-H" is important) is rated for 15,000 BTU/hr output at -26C, and keeps on going no matter how cold it gets. The -xxRLS2-H series is probably your best bet on the mini-splits. The Mitsubishi MSZ-FE18NA has comparable output as the AOU15RLS2-H at -25C, but it actively turns itself off when it drops below about -27C.
While those very-low temps are somewhat rare in your neighborhood and usually very short lived, they're not unheard of. Weatherspark.com data indicate it got down to -32C on Peterborough on the morning of 17 January 2011.
Wow!!! Great info ..thanks a lot .I have been looking at Mits and the new Fujitsu series as my heat source ...I also have a propane fireplace as back up ...regards,Bob