On 10 Sep 2006 14:22:12 -0700, "marson" wrote:

i'm about to embark on a project involving building a superinsulated
house with double 2x4 wall construction. The walls will be 9" thick
and will be blown with dense pack cellulose. i envision the vb going
on the warm side of the inner wall. i live in a very cold climate. i
have several questions:

which wall is load bearing? i planned on making the outer wall load
bearing, in order to shell up the structure, and adding a second wall
inside after the building is dried in. but what little info i have
been able to find talks about making the inside wall load bearing.
this is from the canadians. anybody know why you would make the inner
wall load bearing?

If you're adding insulation on an existing structure,
adding on the outside means you're sacrificing
less living space, and you don't have to mess with the
utilities. The only reason I can think of to
make the inner wall load-bearing on new construction
is if the 12" of span it buys you means you can use
smaller lumber for the joists and rafters.


where the wall has roof trusses resting on it, is fire blocking
required at the top of the wall? I'm thinking not because it is full
of insulation. i'll ask my inspector, but wonder what you guys think.

anyone know of a website with some construction details? how to handle
the windows has me in a quandry. i'm thinking of oversizing the ro's
by an inch, and making a box of 1/2 inch plywood inside them (the
window would then sit inside this box). this would allow me to foam
the window to the box, and then caulk the vb to the box. trouble is,
nailing off the window into the edge of this plywood box may be
problematic. i'm also wondering if there would be value in putting a
9" rip of plywood on the top of the outer wall, expecially on the 2nd
story to prevent convection from the wall cavity into the attic.

The people who do straw-bale construction have a bunch of different
strategies for doing deep windows, I'd be tempted to flare the
opening between 15 and 30 degrees on the sides and top, and
choose/build windows with internal insulated shutters.


if anyone's been there done that, i'd appreciate some tips. also,
please don't waste your time telling me i'm stupid for going double
wall--the architect and owner came up with this...i just build em.