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

[Eli Talking]

Thanks so much for the great response to my inquiry.

I did design a double stud wall similar to Rob Tom's description in 2008. 
So far, the clients are happy with the result.  As is sadly the case, often 
new details are hard to achieve with subcontractors that are old school.  In 
my design, we built a conventional structural 2x4 wall and roof truss 
framing.  I then located another non structural 2x4 wall to create 12" wall 
with 6" space between inner most surface of studs.  I left the cavity open 
at the truss so that loose fill insulation in wass could be continuous with 
loose fill insulation in attic.  I was hoping to install cellulose extra 
thick over the walls to allow for settling without creating a gap. My 
clients were owner builders and were highly motivated.  However, insulation 
contractor convinced them that the weight of cellulose would blow out the 
wall paneling.  Therefore, the settled for full thickness of fiberglass.  I 
am certain they did as good a job as was possible to fill in all voids. 
However, they included the classic flaws of holes in the drywall for 
switches, receptacles and plumbing.  At recently as 2008, I was not fully 
aware of the importance of air sealing.  Likely the building wrap was 
installed months before siding went up and was not taped.  This house also 
featured a suspended concrete slab that works great for tempering the swings 
in the house.  However, the lack of an affective continuous air barrier 
likely allows passive draft into the house.  Since we did not install active 
fresh air ventilation and they have not complained about being stuffy, 
indicates there is typical draft that I want to avoid.  Yes, these issues 
can be addressed with greater awareness of continuous air barrier.  Wires 
and recepticles could be kept out of wall.  Drywall and building wrap could 
be managed more carefully to achieve continuity.  However, there are plenty 
of opportunities for imperfection.  I can appreciate the organic source for 
the cellulose as opposed to plast-ecchhh! as you call it.  However, the 
strong benefit of foam insulation is that it is a thick air barrier that 
maintains a surface temperature near the air temperature on both sides of 
the thermal insulation.  Therefore, when the heat flow reverses from summer 
the winter, the warm side is always close to air temp, affectively avoiding 
condensation threats.  Outside mounting allows affective continuity like the 
drink ice cooler that avoids sweat on hot humid day by achieving exterior 
surface temp near ambient. The furring strips are the material alternative 
to second stud wall.

John Straub, thank you so much for your information.  It is reassuring to 
hear your support for this approach.  When we seek to improve upon common 
practice, we are taking a risk.  Your experience is very valuable.  I 
appreciate your willingness to share and promote what you have found to be 
good practice and make us aware of the failures you have discovered.  I have 
your book.

John Salmon, I will be studying your comments to evaluate the different 
outgassing certification programs for sheathing.  I will also study the 
potential for adhesives as a supplement or alternative to mechanical 
fasteners.

Eli
www.conservationarchitect.net


-----Original Message----- 
From: RT
Sent: Wednesday, November 28, 2012 12:00 PM
To: Green Building
Subject: [Greenbuilding] (not) Re: Outgassing of Sheathing & 
Insulationfasteners

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

< A r c h i L o g i c  at  Y a h o o  dot  c a  >
(manually winnow the chaff from my edress if you hit "reply")

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