I'm prepping to put in a pellet insert and the manufacturer specs R of at least 3 for the hearth, which is pretty darn high. Right now there is some bluestone over some type of unknown sheet material, this certainly will not meet it, so i am going to gut it and fab my own. My question is does the hearth through and through have to be made of non combustible material? If so, this will be difficult, in fact I'm not even sure how to do it other then making it very thick (6" on wonder board) or searching out some hard to get material (microcore 160). I would prefer instead to meet the R value with traditional lumber with insulation and tile/stone top over say 1/2" of wonderboard, I would probably end up with a finished height of <3", but this would use combustible material, is that OK?
Oh and I see a lot of posts with folks using steel studs, noncombustible yes, but LOW R value!
Oh and I see a lot of posts with folks using steel studs, noncombustible yes, but LOW R value!