2×4 exterior walls in 85# snowload area?
Long time subscriber. usually hang out in GBA site but I need some real framing guidance. I am a licensed contractor in MA who works solo on small projects so this is out of my area of expertise.
I am About to break ground on my retirement home in the lower section of White mtns. NH. My Architect (and his engineer?) claim I cannot do an exterior 2×4 load bearing wall on this build. This is a double stud wall (Kolbert P.G.H. style) with R-40 cellulose. I plan to have plywood gussets connecting the 2 walls. Now, the only reason I can think of that the architect would not spec out 2×4 exterior wall is the 85# snow load for that area (I am near highway 93 level).
The 2018 IRC code says a 2×4 wall can be used to carry 1 floor and a roof above…as well as just a roof alone, BUT, the code also only goes up to a 70 psf for ground snow load.
There is NO BUILING INSPECTOR in town to ask. Houses are built way below code all the time here.
A few details on the build. Modified cape 26×48 with large shed dormers front/back.
TJI 1st floor joists. Open web Floor truss for 2nd floor joists.
The roof was designed for stick build by engineer….but I have changed my mind on that after learning I needed a ridge beam…I Now have a price on Roof trusses.
I do not have the header spec sizes yet from lumber yard so it is possible I need 3ply 12″LVL to go over the 8′ slider…..In which case I must use 2×6 exterior wall.
My reasons wanting to use 2×4 wall instead are cost, and their lighter weight of standing walls.
Thanks to any who can enlighten me.
Replies
As a MA licensed structural engineer, I'd offer my thoughts.
Be picky about the 2x4 studs that you use. Pick the best grade that you can and don't settle for "Utility." I'd go for LVLs as king studs (for straightness & a bit of extra stiffness). Since there's no drywall in the inside of the outer wall studs, I'd install blocking at every horizontal sheathing joint and profusely nail the sheathing edges into the blocking. This will help to stiffen the studs against bucking. I would want to evaluate the top plates to be sure they're adequate for the roof truss load applied to them.
Be careful with the inside corner drywall joint between the ceiling & wall - this is apt to crack because of the minute deflection of the trusses at this location. Perhaps a reveal (there are trim pieces for this) at the edge of the ceiling drywall will allow for slight movement without affecting the drywall.
Talk to the truss designer to be sure that the trusses are designed to bear on the outer 2x4 wall - they may choose to reduce the design span thinking that the inner 2x4 wall is a support and it'll reduce the span.
So not framing in 2x4's all comes down to a header over one door? Can you double the rim joist for the 2nd floor and use that as the header over the door?
You can always install a flush header in a bearing wall. Put the header on top of the wall and use joist hangers for the joists. Strap it to the rim joist if needed
Thanks for reply. I hope to do just as described above and bury the headers in the band joist and hang the floor joists from them as needed.
I would either like to do exterior bearing wall 2x4 16oc. which fits the needs of the siding specs which need 16oc.
Or 2x6 exterior wall 24oc is my next option. In this scenario, I would be attaching rain screen fir strips 12" oc. Half of those would be screwed to the CDX sheathing only in between the 24oc studs....not ideal.