Double stud-wall construction: inner or outer load-bearing wall?
I have been investigating a lot of framing options to achieve a relatively inexpensive, high r-value wall and have decided on building a double stud-wall made of 2-2×4 walls with a 7.25″ space in between (to achieve what I want for an r-value). I have come across differing methods of distributing the load from above; inner versus outer load bearing wall, or a combination of the two (inner for the second floor joists and outer for the roof trusses). And then there is Larsen Truss construction. This also dictates the foundation below and the complexities that can exist regarding thermal breaks from the concrete. Right now I’m thinking of an inner load-bearing wall but a foundation wall for each wall (with 6″ EPS foam in between them for a superior thermal break). Thoughts on load-bearing options?
Thanks.
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if you are going with foam instead of, say, dense-packed cellulose, have you considered a REMOTE wall instead? Here is one of the 10,000 links on the web, if you are not familiar w/ it. Either way, good job on insulating well! http://www.cchrc.org/docs/northern/Northern_Fundamentals_REMOTE.pdf
matthew,
on a passivhaus we were asked to consult on, client wanted double stud walls (they've been using them on other projects). we utilized the exterior leaf as load bearing, inner leaf isn't load bearing. it took us a few passes, but we were able to figure out a thermal-bridge free wall/floor detail that ended up being relatively easy to build. it's a PH, so in terms of continuous air barrier proved a little tricky (ours is exterior sheathing) than one would like.
the builder really liked this solution - there was really no change to how they do things, other than some added foam underneath and better attention to detail at construction joints. plus it should be durable w/ the exposed concrete (rather than exposed insulation w/ parge coat or fiber cement board). here's the detail done in THERM:
http://bruteforcecollaborative.com/wordpress/wp-content/uploads/2012/04/1115_ThermDetail_SlabWall_ColorInfrared-500x499.jpg
Matthew,
It's possible to design your double-stud walls either way: with either the inner or outer wall being the load-bearing wall. If you aren't sure of the ramifications of your preferred design, it's best to consult an engineer.
For more information on GBA, see these articles:
Details for double-stud walls: Building Plans for Double-Stud Wall Construction
GBA Encyclopedia article: Double-Stud Walls
Q&A Spotlight: Is Double Stud-Wall Construction the Path to Efficiency on a Budget?
Article by Rachel Wagner in Fine Homebuilding: Double-stud walls
Matthew,
Just thought I'd add that in my opinion the load bearing structure should be either the inner or outter wall (whichever you prefer), but not a combination of both.