[Greenbuilding] voluminous wall cavities - limits to what one

[LarenCorie]

From: Reuben Deumling <9watts at gmail.com>

> I understand that it is possible with thick walls (10-1/4" in my case) to
> find oneself unable to achieve a dense pack if the cavities are too
> wide/one doesn't create enough baffles.

Hi Reuben;

   I have not encountered such a problem.  Use insulation netting
(if it will be inspected) and fill at the first hole, until you get 
adequate
pressure.     Then fill at another hole until you get adequate pressure.
Baffling is not needed. Just fill until the cellulose creates the proper
back pressure at all the holes.

 Get a bid from a cellulose contractor. I have found that they
may do the job (for double walls and thick cathedral ceilings)
for cheaper than you can buy the materials (retail)..

>  In the case at hand I am in the process of building a double wall
> (2x6 load-bearing interior, 2x4 ~Larssen truss exterior) with about
> an inch and a quarter gap between the two walls.

That is a lot of insulation for your climate, especially with foam 
sheathing.

> The cavities are between 40 and 60 inches tall and 10-1/4" thick

Why so short?  Are these kneewall?  The lack of height, in itself,
is a form of baffling. Tall walls (>9ft) require three holes vertically.
Your situation will not.  Only use two holes, about a foot from the
bottom, and 6-8" from the top of the cavity.      Fill at every stud
space, to be sure that the whole wall is adequately dense packed.

> if as I intend to I staple mesh across those narrow gaps. Is this 
> adequate?

   Only use insulation netting on the interior face of the interior studs.
Use adhesive to glue it, before blowing in the insulation, or you will
be really sorry, when your drywall won't touch the studs.

> should I staple mesh *between *the interior and exterior wall assemblies
> and figure out a way to blow cellulose into each separately?

  No.  The wall can be one big cavity. But, you still need to blow
and pressurize every stud space (top and bottom) as if they were
separated by full studs.  In that sense, cellulose is "self-baffling"

 -Laren Corie-
 Natural Solar Building Design and
 Solar Heating/Natural Cooling/Energy
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