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My timberframers are recommending a stress skin panel made by a company out of Fond-du-Lac Wi that uses Expanded foam(the white kind) for their panels. The tech heads I talked to there said the chief reason was because their parent company makes Expanded foam. They’re saying a nominal 12″ panel (11 1/4″) is R46, will support 64 lbs/sq ft at a nine ft span between trusses and costs $4.00 per square ft. That’s with 7/16″ OSB on both sides.
Does this like it will work and is it a good deal? I always thought Expanded was a little weaker than Extruded.
The Wood Doc
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The main concern I would have is a failure in the exterior skin.
Water penetration into the white beaded insulation would spell disaster during freeze thaw cycles.
Just a thought
Gabe
*Here's link on our topic: http://www.eren.doe.gov/consumerinfo/refbriefs/bd1.htmlThe relevant paragraphs:i EPS and XPS Panelsi The majority of SIPs are manufactured with expanded polystyrene (EPS.) This foam is commonly known as beadboard. This type of SIP has a nominal R-value of about 4 per inch (2.5 cm) of thickness. Unlike other types of foam insulation, beadboard uses pentane as the expanding agent. Extruded Polystyrene (XPS), with R values of 5 per inch (2.5 cm) of thickness is also sometimes found. It uses a hydrochlorofluorocarbon (HCFC) gas as the expanding agent.Basically, the beadboard is the cheapest of the faom boards. There's also a type where they place the panels and shoot expanding polyurethane between them (expensive and rare). The foam board ones are laminated and glued together. SIPA -- Structural Insulated Panel Assoc. -- is also a good source of info.
*The stress in any thing rigid is carried by the outermost fibers.So, I guess that the kind of foam used is not a real big factor in the overall strength of an SIP. I think that the type of foam has most to do with the R value, water resistance, the kind of equipment the mfr has invested in and stuff like that.Strength-wise, the key factors are gonna be(in this order): - thickness of the OSB layers - quality of bond between the OSB and the foam - thickness of the foam - stiffness of the foam
*correction!the biggest factor will be the DISTANCE between the two outer layers, then the strength of those layers.so the order should be:- thickness of the foam- thickness of the OSB layers - quality of bond between the OSB and the foam - stiffness of the foam
*I spoke with the tech heads today in regards to fire resistance of the panels. He said that in the last seven years he only remembers one job that installed drywall. I am planning on putting 3/4" T&G paneling on the inside which he said would increase the burn thru time compared to just 7/16" OSBI'm wondering if putting up 1/2" fire rated drywall then 3/4" T&G prior to craning(is that a word?)would be a smart idea. He said another option is having the OSB manufacturer add a 3/16 cementious coating to the inside which should give an additional 15 minutes of fire resistance. This would bumb up the cost about 75cents per sq ft. Any Thoughts?The Wood Doctor