2x6 staggered studs in 8" stud wall design 3

[swm25]

I have a wood stud wall design in which the wall will be 8" thick, but it will be built with 2x6 studs that are staggered between the interior face and the exterior face of the wall, the idea is that more insulation can be installed in the wall, and that there will be a thermal break.

The problem is that only one face of each stud will be tied into sheathing, one stud will be nailed into the exterior sheathing and the next to the interior. I am wondering if anybody knows how to model the bracing of the weak axis for a stud wall of this type, or if they know of any provisions for stud walls that are only braced/sheathed from one side.

 

[Ron]

You have more than a modeling problem. For fire resistance ratings, the sheathing has to be fully blocked. Further, if you are putting a solid cladding such as stucco, you need to limit the sheathing deflection to minimize stucco cracking.

 

[concretemasonry]

It is a code acceptance problem and not a structural problem since many details are prescriptive and not performance for the application.

Of course, a PE can over-ride most prescriptive things on a structural situation.

Dick

 

[swm25]

I didn't mention that the studs would be placed 12" o.c. at least for the preliminary layout, thus each face of sheathing would be fastened to a stud at 24" o.c., the stucco concern is a good note, and I'll need to verify that it has sufficient stiffness for the stucco.

 

[Ron]

Check with your local AHJ...you might be required to install gypsum board and exterior sheathing vertically instead of horizontally for this application. Check your span ratings both ways.

 

[msquared48]

With the 2X8 plate and 2X6 studs, there should be 2" available to install flat blocking for the sheathing with still a 1/2" gap for sound.

Mike McCann
MMC Engineering

 

[boo1]

Consider exterior rigid foam sheathing as a more effective thermal break. It will also save two inches of inside peremeter space.

http://building.dow.com/na/en/products/insulation/rigidfoam.htm

 

[swm25]

I think that rigid foam would be a good idea, but it isn't my call on this one, this is the Architects decision, and they're doing it for their own new office building so I think they're trying to do something inovative. I've thought about using steel straps (similar to how cold formed steel Z sections are braced) that could weave back and forth to the unbraced sides of the studs, and then have some kind of beam at the end of the wall to resolve the force. The trouble would be how to calculate the buckling force of a wood member. Does anybody have experience with this?, any other ideas would be great too.

 

[Ron]

If you look at the fire resistance requirements for this type of wall (Check UL U340), you need to brace the studs at the mid height. That should be sufficient for buckling purposes.

I like your edge bracing idea with the channel straps.

 

[csd72]

a vertically oriented timber brace along the middle will brace the inside of the studs

 

[msquared48]

In a soundwall of this type, the last vertical member of the wall will be either one or two 2X8 studs. The force from the weaving of the strapping could be taken by the 2X8's, stiffened since they see sheathing on both 1.5" faces. No worries. I like the weaving idea too.

The only drawback is interference with the installation of any insulation. But this is not impossible to get around, just a little mo effort for the insulation contractor.

Mike McCann
MMC Engineering