[Greenbuilding] (not) Re: Outgassing of Sheathing & Insulation fasteners

[RT]

On Wed, 28 Nov 2012 09:48:23 -0500, Eli Talking  
<elitalking at rockbridge.net> wrote:

>  In the house I am  designing, we are planning on putting all the  
> insulation on the outside, 6” or 8” EPS, still to be determined.

> 2x furring

> I am wanting to know if the  withdrawal strength of .5” plywood or osb  
> would be sufficient.

I'd have to check some old timber engineering texts for the w/d strengths  
of the various sheathings(which you could do yourself and probably on the  
WWWeb these days) but I wouldn't rely upon either for any significant  
withdrawal resistance unless using a very,very coarse-threaded screw -- so  
coarse that it'd require pre-drilling humongous holes to accommodate the  
thread (leaving a large-ish void around the unthreaded shank of the screw  
where it passes through the 2x furring.

If one is going to be installing 6 or 8 inches of EPS insulation on the  
outside presumably of a stick-framed 2x4 or 2x6 wall and then install 2x  
furring on top of that, I do have to wonder why one wouldn't simply do a  
double-stud wall  (ie 2x4 @16" o/c bearing wall + 2x3 @24" o/c curtain  
wall, spaced apart by a minumum of 3.5" (and no practical maximum) of  
continuous insulation unbroken by framing ... curtain wall and bearing  
wall joined by 1/2" ply flanges at top plate & sill plate + 3/8" ply or  
11mm OSB @ door & window openings ... all assembled on the floor deck and  
tilted-up together as with single-stud assemblies) and fill the cavity  
with either batts or blown-in fibrous insulation thereby avoiding the  
higher cost of the foamed plast-ecchhh! insulation and all of the  
associated headaches (ie window detailing for one) in having to futz with  
that foam ?

If using batt insulation, it can be installed in the curtain wall framing  
and in the continuous insulation layer between the walls while the wall is  
still laying on the deck, with the air barrier located at the outside  
plane of the bearing wall.

Once tilted up, such walls are stiff enough and fat enough that they  
almost don't need any temporary bracing to remain straight and plumb while  
interior partitions and upper-storey framing are being built.

Also, since the wall air barrier is complete and out of harm's way once  
the walls are tilted up, services can be installed in the bearing wall  
without having to worry about what the sub-trades do or don't do.

Of course, if one has the hots for foamed plast-eccchh! insulation,  
there's no rule that says it can't be inserted in the continuous  
insulation space between the two walls instead of fibrous insulation.

-- 
=== * ===
Rob Tom					AOD257
Kanata, Ontario, Canada

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