Long time lurker. Been trying to absorb as much information as I can. However, the time has come to come out of the bushes and make myself known. My primary questions revolve around building the hearth pad. I am installing an Englander 30NCH wood burning stove. The required R Value is 1.5. My install location will be on the main level of the home that has a wood sub-floor (plywood on floor joists 16” on center). I see that a lot of people have used Micore in their pads. I am finding this very difficult to source. Yes, I can find it online, but I do not need 4 sheets of the stuff. So here are my plans/questions. I am going to raise the hearth on some 2X4s. Should I use wood or metal studs? I have zero experience with metal studs. Does the “air space” created by metal studs count in the final R-Value calculation? I was then going to layer Durock on top of the 2X4s. The number of layers will depend of if the air space can or cannot be included in the R-value calculation. If not I think I need four ½” layers. The plan is to then tile the surface. What would be the maximum on center spacing needed to give adequate support for the Durock? Thanks in advance for any advice and/or direction.