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:

Consider putting the vb on the cold side of the inner wall. General
recommendation has been (for a cold climate) to have 2/3 of the
insulation on the cold side of the vb, so you should be ok. That would
help with the matter of electrical and plumbing folks leaving all sorts
of penetrations in the vb. They would have the inner wall space to do
their work. Afterward, you can use 3.5" FG batts there before the
sheetrock goes on. I wouldn't use FG in the bigger cavity, because
especially as the wall gets thicker the density difference in the air
next to the sheathing on a cold day vs. the warm air next to the inside
is substantial, setting up small air currents within the FG batt and
hurting its effectiveness, unless it is more dense. The blown
cellulose, to 3 lb/cu.ft density, is said not to suffer from this
problem.

I assume you will have something like XPS covering the foundation wall
on a house like this. What will you be doing on the outer wall so that
the siding goes over the outside of the XPS?