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<DIV>Thanks John for replying to my message. I work in a mixed climate of
Western Virginia. </DIV>
<DIV> </DIV>
<DIV>Coming from you, I take your comments about the fluctuation of humidity in
framing outside the thermal envelope very seriously. My thought was that I
am creating a similar condition to drafty old houses that never rot because they
have lots of air flowing through them. Therefore whatever weather driven
moisture gets through the siding will dry out. My intention was to put
flashing at the bottom of the wall to drain any bulk liquid. However, I
have not considered the impact of fluctuating humidity on the dimension of the
framing that my proposed panels were to cover to the interior. So I may
reconsider. John, in you considerable experience have you seen the
interior approach tried similar to what I describe?</DIV>
<DIV> </DIV>
<DIV>I have renovated my home that had conventional fiberglass batts and plywood
sheathing by installing 3” iso foam and mounting 3”x3/4” sheathing strips
to mount plywood siding to. This is similar to what you
recommend. In the future with this approach I would likely use 2x3’s
for furring. If the attic is kept inside the thermal envelope, I will
continue the insulation over the roof sheathing avoiding thermal bridge at
eave. If using eps foam, I would ventilate with purlins under metal roof
and design positive draft ventilation to carry away any interior driven vapor
that would migrate through the eps foam. </DIV>
<DIV> </DIV>
<DIV>This house in South Carolina had trouble with rotting osb above a rafter
cavity filled with vapor permeable open cell foam. <A
title=http://www.greenbuildingadvisor.com/blogs/dept/musings/open-cell-spray-foam-and-damp-roof-sheathing
href="http://www.greenbuildingadvisor.com/blogs/dept/musings/open-cell-spray-foam-and-damp-roof-sheathing">http://www.greenbuildingadvisor.com/blogs/dept/musings/open-cell-spray-foam-and-damp-roof-sheathing</A></DIV>
<DIV>This article does not give firm conclusions. The solution this author
proposes of creating a vapor armor using closed cell foam, is one
approach. However, I believe the problem was that building paper acted as
a vapor barrier, raising the dew point and hence condensation and rotting.
I would propose that this problem would not have occurred if the vapor had space
to draft out once it had migrated through the foam. If installed properly,
the interior draft would only be vapor, not air. The air draft would come
completely from exterior air. Therefore the ventilation above the foam
does not increase air draft in the building. I am curious to know if
vapor that condenses inside a vapor permeable foam can evaporate again and
continue drafting through once the temperature has risen. </DIV>
<DIV> </DIV>
<DIV>John’s Comment:</DIV>
<DIV>The approach does solve the rather major thermal bridges of the floor
penetrations throough the wall. It does breaks the thermal bridge of the
plates and studs though. </DIV>
<DIV> </DIV>
<DIV>My Comment:</DIV>
<DIV>A multiple story building would still have thermal bridging of joist
penetrating the thermal envelope. I would have professional insulators
install open cell foam. However at the bottom floor and at the top flat
ceiling allows perfect continuity(no thermal bridges). The problems
I have become aware of with tight houses that have siding nailed directly to
sheathing that that has solid foam on the other side, is that weather driven
moisture gets trapped in them and the common practice draft through the house is
not available to dry it out, causing rot. </DIV>
<DIV> </DIV>
<DIV>My incentive for the method I was describing was to eliminate one layer of
framing by making the structure and the drain dry plain the same. Also, I
was looking for the panels to allow a possible retrofit application.
However, your comments give me cause for concern. </DIV>
<DIV> </DIV>
<DIV>Eli </DIV>
<DIV> </DIV>
<DIV> </DIV>
<DIV>-----Original Message----- </DIV>
<DIV>From: John Straube </DIV>
<DIV>Sent: Monday, June 23, 2014 9:05 PM </DIV>
<DIV>To: Green Building </DIV>
<DIV>Subject: Re: [Greenbuilding] Veneer Foam Panels </DIV>
<DIV> </DIV>
<DIV>The approach does solve the rather major thermal bridges of the floor
penetrations throough the wall. It does breaks the thermal bridge of the
plates and studs though.</DIV>
<DIV>It places the main structure to the exterior, and hence exposes it wild
swings in temp and RH with attendant movement and durability issues. Major
problem with all interior insulation solutions.</DIV>
<DIV>I dont know what “drafting air” through the studs means but it does not
sound like a good idea :)</DIV>
<DIV> </DIV>
<DIV>Which leads to the question, why would you try to do this? It is so easy to
place the interior finish, veneer grade plywood, drywall, MDF, etc. on the
interior of the studs of a normal high performance wood frame enclosure (see
building science.com). Why not do that? It is easy to add EPS to the
exterior of the framing, no gluing needed. This protects the framing from
temperature and humidity swings. It allows the air -water barrier to be placed
over the framing, and yet protects the air-water barrier from the worse
temperature extremes, thereby adding longevity and reducing the risk of cold
weather condensation. All that is needed is to add furring strips screwed
through the exterior insulation, otherwise almost everything is the same as
normal construction. And exterior insulation improves the durability and
performance all round.</DIV>
<DIV> </DIV>
<DIV>John</DIV>
<DIV> </DIV>
<DIV>On Jun 23, 2014, at 7:34 PM, <conservationarchitect@rockbridge.net>
<conservationarchitect@rockbridge.net> wrote:</DIV>
<DIV> </DIV>
<DIV>> I am interested in bonding a veneer grade plywood to a 4 to 6 inch
thick panel of EPS foam that could be set to the interior of building framing to
achieve a continuous thermal barrier. I am wanting the beauty of the wood
to replace the need for conventional sheetrock so this can be the finished
surface. I think that the thickness of the foam bonded to the plywood
makes both more rigid and able to take some loading. Although, unlike SIPs
I want the main structure to be separate from the insulation (thermal
barrier). I am wondering if using low investment methods such as spreading
foam appropriate panel adhesive over eps foam laid flat would achieve adequate
bonding. I am also wondering if humidity is a factor in bonding and or
dimensional stability. I would seal the seams. The seams would be covered
with a finish grade wood strip.</DIV>
<DIV>> </DIV>
<DIV>> If I had the structural sheathing (osb or plywood) to the interior
side of conventional wood framing, siding could be mounted directly onto the
framing to allow for drafting in the cavity which can serve as the drain dry
plain that is needed if we are not drafting heated air through the wall.</DIV>
<DIV>> </DIV>
<DIV>> The intention is to set these panels on the floor framing to be
primarily self supporting avoiding the need for the long fasteners that drive up
cost and likely reduce thermal performance. In some cases, I would use the
flat ceiling for the top of the thermal barrier. I was interested in
installing some exposed ceiling rafters that would be supported by a ledger
mounted to the wall foam-plywood panels. I would set veneer plywood above
and support thick layer of foam. The loads would be only the rafters, foam
and the plywood. Live load and dead loads from the main roof are carried
by conventional wood trusses. These ceiling rafters wedge the wall
paneling in place. This ceiling assembly can be set in place without
bonding. This also avoids the long fasteners. I would top off the
ceiling foam from the attic side with fire retarded cellulose to serve as the 15
minute fire barrier required by code. </DIV>
<DIV>> _______________________________________________</DIV>
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<DIV> </DIV>
<DIV>John Straube</DIV>
<DIV>www.JohnStraube.com</DIV>
<DIV> </DIV>
<DIV> </DIV>
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