JEuriech 0 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 post Share on other sites
Marc 77 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 post Share on other sites
kurt 2 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 post Share on other sites
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