[GBlist] wood wall system

["Matt" <m.tymoshuk@home.com>]

I'm going to be building a S.O.G.  wood framed home next summer and would
like some ideas on a wall system that is as envrio-friendly as possible and
around R30. In terms of building materials the recycled content, embodied
energy and pollution problems of wall systems should make this method as
close to straw as any other...

The best I have come up with is a in-line finger joint stud wall with O.S.B
sheathing and blown in cellulose insulation completed as follows:

2x6 studs 24" o/c
3/8" O.S.B exterior seathing
2x2 horizontal strapping on the inside of exterior walls

My idea is to cut up the "greenest" 1" thick ridged foam into 2"x2" blocks
and use them as spacers between the wall studs and strapping. This would
create a thermal break between the 2 wood members. To contain the blown in
cellulose a continuos 3" strip of  foam would cover the top and bottom
plates, around window and door framing with the strapping nailed on top.  A
1/2" x 6" strip of foam board would sit under the bottom plate to create a
break with the S.O.G. If the rim joist is pushed in 2" from the outside wall
surface foam could be placed there to break the rim along with a 1/2" strip
of foam on top of the 1st partition plate.

The wall would be aprox. R 30.4  ie. 5.5" studs, 1" ridgid foam spacers,
1.5" strapping total of 8" x 3.8R/inch = 30.4R

Housewrap would be placed over the O.S.B, then strapping for some type of
siding. I will more than likely put a 3ft skirt of stone/brick completly
around the home to prevent premature wear from snow and rain for the siding
above.

One problem with this wall is that the thermal break is 5.5" into the wall.
However, the 24" centres may compensate. This wall should be very easy to
build and reduce the use of ridgid board to a minimum. As far as cost, it
may not be to much more that a 2x6 wall with 2" of foam board, since the
board is so expensive and taping the seams may not create a long lasting air
barrier.

A second problem is that the wall cavities are broken up and when blowing in
the insulation pressurization may not be possible???

A third problem would be the requirement of window and door jamb extensions
for the 8" wall.

Any thoughts would be greatly appritiated.

Matt Tymoshuk


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