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-   -   Avoiding load on inner, exterior wall (http://www.diychatroom.com/f19/avoiding-load-inner-exterior-wall-106544/)

jklingel 06-04-2011 01:45 AM

Avoiding load on inner, exterior wall
 
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The latest iteration in my planned house's exterior wall is as pictured, sans a few details that are not necessary for this discussion. The interior is to the right of the 2x4 wall in the picture. The hope is to load only the outer, exterior wall; 2x6 studs will be directly under each truss. My concern is to avoid loading the interior, 2x4 wall if at all possible. The inner, 2x4 wall will have plywood on the outside to serve as an air barrier. That plywood will contact a layer of plywood that will be fastened to the bottom of the trusses, creating a continuous air barrier once all is gooed and taped. My plan is to not fasten the ceiling plywood to the trusses w/in 18" of the 2x4 wall so that the plywood can flex, much as you do w/ sheet rock. I am hoping that any truss uplift, minimal as it may be that close to the bearing wall, will thus not affect the air sealing at the top of the 2x4 wall. The 2x4 wall will be approximately 1/4" shorter than the 2x6 wall, so that any downward flexing in the truss will not load that wall. I will have some kind of "slip plate" holding the 2x4 wall to the truss, so that the 2x4 wall does not fall over. (In addition, there will be many plywood gussets between the 2x6 wall and the 2x4 wall, as per a Larsen or Riversong truss.) So the Big Q is, does anyone see any structural problem w/ this set up? This is not something that I have dreamed up entirely, btw; the basic concept is well established. This is just a slight twist on anything I have seen so far. Thanks for any comments, and if this is not clear, just speak up and I'll explain it better.... I hope.

jomama45 06-04-2011 06:49 AM

I wouldn't use 15 psi foam under any concrete floor, especially if you'll be going with 10". 25 psi, or even higher, should be fairly easy to locate.

jklingel 06-04-2011 01:35 PM

jo: thanks. 15 psi foam is spooky to me, too, but the compression load at 1% deflection is about 6 psi while the concrete will load about 3. 15 psi is what is typically used here, but i am sure leaning toward 25 just for stink and giggles. i can get it as high as 60 psi (at 10% compression, roughly 25 psi at 1%) but it is naturally much more spendy. j


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