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Can I put exterior sheathing over 1 1/2" rigid insulation on an exterior wall w/o hurting the structural integrity of the house?

I want to put 1 1/2" rigid insulation on the exterior walls of a new home I will be building soon to help with the thermal transfer. I have used it before but have always put the rigid over the sheathing then strapping over the rigid. I would like to eliminate the strapping and put the rigid on the studs then the aspenite over the rigid. I would screw the aspenite to the studs but am concerned that the walls might loose some ridigity and strength. I am using vinyl siding so my other option is to use a longer siding nail and put the rigid over the aspenite. Any thoughts or concerns with this would be helpful.

Asked by Mark Audette
Posted Jan 16, 2013 8:59 PM ET
Edited Jan 17, 2013 5:10 AM ET

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2 Answers

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1.

Not without an engineer's report and structural bracing. The APA is currently doing a study for 1" rigid foam between wood sheathing and framing members, but the study is not finished yet (I believe). All they have approved in the past is 1" rigid foam between wood panel siding and framing members. You can download all that info at the www.apa.org, after you register.
Even when it gets approved, I believe to be the wrong application, as the rigid foam should be installed to the outside of the wood sheathing to avoid thermal bridging and possible condensation.

Answered by Armando Cobo
Posted Jan 17, 2013 12:40 AM ET

2.

Mark,
Armando is right. The basic problem with your plan is that you usually need the OSB to be fastened directly to the studs to provide bracing.

If you install the OSB first, and they you install the rigid foam, you can install vinyl siding on top of the 1 1/2-inch-thick foam without any furring strips.

Answered by Martin Holladay, GBA Advisor
Posted Jan 17, 2013 5:06 AM ET

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