JEuriech Posted January 29, 2012 Report Share Posted January 29, 2012 How do you go about determining the "R" rating on a sprayed foam attic ceiling? The minimum rating here for an attic is R-30. Does 4-5" equal an R-30 rating? I could not find an insulation certificate to use. Thanks, Jeff Euriech Peoria Arizona Download Attachment: 1A SF 11.JPG 439.28 KB Download Attachment: 1A SF 13.JPG 416.02 KB Quote Link to comment Share on other sites More sharing options...
Marc Posted January 29, 2012 Report Share Posted January 29, 2012 According to Mason Knowles in a September 2010 JLC article, the R-value of SPF depends on the density of the foam and the blowing agent used. Low density foam in the 0.4 to 0.6 lb/cubic foot range typically has an R-value of 3.5 to 3.8 per inch. Densities of 1.5 to 2.0 lb/cubic foot yields R-values of 5.8 to 6.8. So folk, git dat density and dat thickness and figure dem out. Marc PS: second paragraph ain't by Knowles, none. Quote Link to comment Share on other sites More sharing options...
kurt Posted January 29, 2012 Report Share Posted January 29, 2012 Closed cell foam is hard, almost a shiny film on top. Very hard to tear off a chunk. It's Great Stuff without the can. Open cell is kinda......open.....fluffy....you can dig at it with your fingernail and it'll come off in a chunk. Open cell is about R3 or 4. Closed cell is about R6-ish to 7-ish. Some of the pics look like closed, some look like open. The underside of the roof shot looks like closed cell. But, don't go by my guessing @ a pic. Quote Link to comment Share on other sites More sharing options...
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