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How do I get an R-20 wood wall?

Insulation method to get R-20 in a 2x4 framed wood stud wall?

Asked by Diego Gutierrez
Posted Fri, 11/30/2012 - 09:12
Edited Fri, 11/30/2012 - 10:02

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2 Answers

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1.
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Closed cell spray foam will get you there.

Answered by michael maines
Posted Fri, 11/30/2012 - 09:45

2.
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Closed cell spray might get you to R20 center cavity, but the severe thermal bridging of 3-3.5" studs brings the whole-wall performance down to R11-12, even at a full 3.5" depth, and including the gypsum & siding. By contrast a full 3.5" of cellulose or open cell foam is still in the R9.5-10 range, a difference that could be made up with half-inch rigid foam (any type) on the exterior at much lower cost.

To hit ~R20 whole-wall with 2x4 framing put 2" of rigid polyiso on the outside of the sheathing and cellulose or open cell foam in the wall cavities.

Answered by Dana Dorsett
Posted Fri, 11/30/2012 - 12:09

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