[Greenbuilding] Veneer Foam Panels

[John Straube]

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.
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.
I dont know what “drafting air” through the studs means but it does not sound like a good idea :)

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.

John

On Jun 23, 2014, at 7:34 PM, <conservationarchitect at rockbridge.net> <conservationarchitect at rockbridge.net> wrote:

> 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.
>  
> 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.
>  
> 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. 
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John Straube
www.JohnStraube.com