[Greenbuilding] How green is cellulose infill? / thermal bridging?

[Clarke Olsen]

I have built double walls like this: 2x4 framing, filled with  
insulation, then covered inside with 1/2" foil faced foam, which is
then strapped with 2x4's flat. All the wiring takes place in this 1.5"  
space, using 4"x4"x1.5" boxes. Taping the foam joints will make it a  
vapor barrier. Drywall goes up vertically, good if your ceiling is over  
8'. Finished wall is the same thickness as  2x6 construction. For  
headers, I replaced the foam with 1/2" plywood, glued and nailed to  
make a hollow (w/insulation)
box beam. For a really well insulated house, I would frame with 2x6's @  
2' oc.
Clarke Olsen

On Jul 11, 2006, at 1:48 PM, Alan Abrams wrote:
> <When I did some modeling of thermal bridging in a standard 2X6 wall, I
> came to the conclusion that a thick layer of foam insulation (1" or  
> more
> - I've used as much as 1.5") is a good practical way to limit the
> effects of thermal bridging.  The second way is to use Advanced Framing
> techniques, which reduce the stacks of framing members at places like
> corners or intersecting walls.  >
>
> as an earnest student of residential building science for the past  
> several
> decades, I've concluded that for conventional stick framed walls, the  
> first
> task is water management.  And foam sheathing --without  
> disproportionately
> complex furring, flashing, extension jambs, caulk joints, and other  
> assorted
> band aids and potential leakage points--compromises that task.  This  
> comment
> is based on real world experience, with real world conditions.  All  
> the r
> value in the world is worthless if the walls leak.
>
> If it's true that a continuous layer of insulation is critical to  
> thermal
> management, it makes more sense to me, to put it on the inside of the
> wall--perhaps even strapping 2x3's perpendicular to the studs, so the
> bridging is limited to 1 1/2" square points.  Let the outside surface  
> be as
> simple and straightforward as possible, to manage water.
>
> Wrt to advanced framing, I've been doing much of it for years before  
> it had
> a name.  driving the carpenters nutz, too, doubling band boards  
> instead of
> conventional headers, drywall clips, single sill plates for windows,  
> etc.
>
> Alan Abrams
>
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