[Greenbuilding] Double-stud wall (was Re: Best bang for the buck in wall insulation)

Alan Abrams alan at abramsdesignbuild.com
Thu Mar 27 16:29:25 CDT 2014


<Logically, the interior wall would be the one designated as load-bearing
even if only because doing so shortens the spans of flexural members like
joists and rafters. When we're talking about fat superinsulated walls, the
difference in span can mean a difference in one joist size.>

taking off from the perspective pasted above, one could quickly arrive at a
Larson type system, where you not only shorten the span of the floor
system, but eliminate it altogether beyond the bearing wall.

OTOH, if the premise is keeping the air barrier in a single vertical
plane--and factoring in the current code obsession with braced wall
systems--I still prefer keeping the air barrier and sheathing--and
therefore the outer stud wall, in a constant plane. all the other previous
points reinforce this--logical integration of windows and doors, combining
air barrier and drainage plane--not to mention--keeping it low tech and
carpenter friendly.

The point about reducing joist depth is well taken: there is value in
"resourcing down." But it is less significant if you're using wood I-beams.
A tree that could provide a nice 2x12 is best left in the forest, but a
little more OSB to take a TJI from 9 1/2" to 11 7/8" is less of an impact.

It's worth mentioning that this strategy derives from Building Science
Corp's design for the NIST Net Zero Energy Test House--a sublime piece of
work, IMO...

-AA

Alan Abrams

*certified professional building designer, AIBDcertified passive house
consultant, PHIUS*
*certified passive house builder, PHIUS*
Abrams Design Build LLC
*sustainable design for intentional living*
cell     202-437-8583
alan at abramsdesignbuild.com
www.abramsdesignbuild.com


On Thu, Mar 27, 2014 at 9:11 AM, Clarke Olsen <prismoidal at gmail.com> wrote:

> The problem with single top headers is that, when triaging the lumber,
> it's hard to find something you feel can be trusted up there all alone...
> 2x3 sounds better then it is: most of them are crap. The other reason to
> make the interior studs bearing is that you can keep the foundation back,
> leaving a very generous overhang to drip past the foam that covers your
> foundation. I used to think I was a hero for putting 2" of blueboard under
> the slab and against the foundation, until I noticed how nice & cool it was
> in summer...
> Clarke Olsen
> clarkeolsendesign.com
> 373 route 203
> Spencertown, NY 12165
> USA
> 518-392-4640
> colsen at taconic.net
>
>
>
>
> On Mar 26, 2014, at 5:55 PM, RT <archilogic at yahoo.ca> wrote:
>
> > On Wed, 26 Mar 2014 11:42:01 -0400, AA-man wrote:
> >
> >> here's where I'm heading ...*OVE stud wall
> >> *a void, width determined by specific space heat demand analysis
> >> *an inner frame wall
> >> *the entire framing cavity filled with DP cellulose
> >
> >
> > The above sounds very much like a double-stud wall section so one should
> choose which of the two frame walls is load-bearing .
> >
> > Logically, the interior wall would be the one designated as load-bearing
> even if only because doing so shortens the spans of flexural members like
> joists and rafters. When we're talking about fat superinsulated walls, the
> difference in span can mean a difference in one joist size.
> >
> > In making the interior wall loadbearing, there's no need for the
> exterior wall to be a 2x6 OVE stud wall -- it can be a 2x3 or 2x4 wall with
> studs at 24" o/c, single top plates, no lintels over openings (assuming
> that we're talking about low-rise residential building)
> >
> > One just needs to ensure that one allows for eventual shrinkage of
> cross-grain framing members (ie sill & top plates, rim joists, lintels) in
> the bearing wall so that the curtain wall does not inadvertantly become
> loadbearing.
> > --
> > === * ===
> > Rob Tom                                       AOD257
> > Kanata, Ontario, Canada
> >
> > < A r c h i L o g i c  at  Y a h o o  dot  c a  >
> > (manually winnow the chaff from my edress if you hit "reply")
> >
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