Hey guys,

I recently saw a method for building exterior walls in a book that I thought was interesting and wondered if anyone had ever used this method or seen it.  The picture in the book showed a 2x6 wall built with 2x6 top and bottom plates but instead of 2x6 studs they used 2x4 studs.  Basically the 2x4's are installed on 16" centers on the outside and inside portion of the plates.  The inside 2x4's are staggered between the outside.  With this method you can insulate the wall and have no thermal breaks.  Also it would make it easier to thread mechanicals.  Please let me know what your opinions are.  Also does anyone build their exterior 2x6 walls on 24" centers?  If you do is bridging required between studs?  Thanks. 

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When I started my house project over a year ago I considered this same approach, with one difference. I was thinking of using a 2 x 4 and a 2 x 2, parallel to each other with 1/2" space between, for both the top and bottom plates and possibly for window and door framing. The whole idea was to avoid thermal bridging, just as you're saying.

Here is the response I received from Dr. Jan Kosny at the Building Technology Center at Oak Ridge National Lab, http://www.ornl.gov/sci/btc/, when I asked for his thoughts about this approach.

"For you double stud wall assembly, please consult structural engineer first. Regarding the thermal effect, you will probably end up with little bet better performance then in case of using regular 2x6 studs. However you will add a lot of extra work and cost to your building."

PM me and I'll forward the entire email I sent him and his response. I asked about frame, ICF, and SIPs. Or, I can post it here if enough folks ask. It is fairly long.

This is a method we used in the 90's for sound barriers, it was for the corridors in apartment buildings, I'm sure it worked, but now we have ICF so I don't worry about it anymore, as Dmaceld pointed out you are creating a thermal break but I doubt the extra costs are a justifyable payback anytime soon, it is slower (Basically framing 8" o.c.) and other than the top plates your doubling your framing costs.

It will certainly work. The key is to insure that you have air infiltration eliminated. A design that I came up with is below. Please note that I used 2 x 4 framing to eliminate the thermal breaks between the top & bottom plates, and only the exterior wall carries the load.

It will work but it will not be cost effective or practical. At this point you would be better off with ICF or SIPs.

Dave

I agree. From a L & M standpoint, the only way that it's economically feasible(over SIPS or ICF's) is for a DIY project where the owner supplies all of the labor.

What about using 2 x 4 walls with a 2 x 2 turned perpendicular (horizontal) to the wall studs? The only thermal bridging would be the areas where they intersect - and would be less labor.