Building a hearth...does this seem reasonable?

The burner has been installed & it's time to start the finish work.

The stove is a zero-clearance insert-type Bis Tradition CE. The top, bottom, both sides, & back of the unit are not an issue. The only non-combustible finishing I need to do is the hearth and facing around the unit. This will be done with Durock. The pic attached is a rough mockup and what I'll be building. The yellowish? area on top is the ceiling. Basic dimensions are 6 feet wide, about 11.5 feet on the left & 14.5 feet on the right. Vertical surfaces will be dry-stacked slate, horizontal of the hearth will be slate tile.




The hearth will be 6 feet wide & about 10 inches high. The hearth assembly I'm considering is below. It'll run around 220 pounds. It'll give me an R value of 1.56 (all the Durock, not counting the slate tile). The Durock layers will be screwed together with 1.25 inch Durock screws & Flexbond thinset. The stove manual only states the hearth must be a non-combustible surface....no R or K values given. The stove puts out a max of 55K Btu with a contiuous output in the 30-35K Btu range. What do you think...is this a sound approach?

Stove front
slate tile (0.375 inch)
0.5 inch Durock
0.5 inch Durock
0.5 inch Durock
0.5 inch Durock
0.5 inch Durock
24 ga galvanized flashing under stove & fully covering hearth area
0.5 inch Durock
6.75 inches dimensional lumber 2-by
subfloor

thoughts anyone?

I'll be making the rounds and picking up all the various materials in a few hours.

thanks,

Thanks to all for your suggestions.

One of the driving forces to have the excessive number of durock layers is that I want to have a roof-flashing ember strip installed...as well as using the flashing over the entire hearth to dissipate heat. If I install the flashing at the bottom of the stove (lift the stove & insert the flashing between the stove bottom & the 2 x 8's it's sitting on) then I have 3.5 inches of filler-space to build up to the hearth surface itself. I suppose another option would be to use larger 2x material as you suggest and make a Z ember strip to insert under the stove, go up a couple inches, and then insert between a couple layers of Durcock. Naturally I don't have a sheet metal break though I could rig something up...maybe start with a piece of heating duct and cut it up. Using larger 2x would certainly be easier than cutting & wrestling durock.

The layers were also building up the R value as a "just in case"..I find it surprising the manual says only "non-combustible" without any reference to insulating from, or dissipating heat.

The mantle will be wood & probably won't look like the pic here, but it will be at the regulation height above the stove front.

This is what it looks like so far: