I reviewed some prior threads and spent some time on-line, and could not come up with R values for bluestone. The Forum has some estimates of 0.08 to 0.15 per 1 inch thickness, but nothing I could use as "official" in case my insurance carrier would like to know. The reason I am asking is that the Hearthstone Heritage, prior to the more recent models of putting it up on taller legs, requires an R of 1.2. My hearth plan is: MATERIAL R VALUE Frame and plywood frame top Nothing 3 layers of 1/2" Durock: 0.39 each 1.17 3 layers of ~ 1/8" Thin set 0.05 each (0.40 per inch) 0.15 Total: 1.32 Then I will have a layer of 1.25" bluestone on top. Knowing the bluestone value would be helpful if using the thinset values raises eyebrows. So if anyone knows, it would be appreciated. Thanks.