Hey, I am building my tiny 12'x12' cabin with lofted space. The ceiling is 13ft. I wish to buy the Englander 17-VL. I will make a ventilated air space to cut on my clearance. The stove will be in a corner. From reading the englander manual and some guides on clearance from combustibles - My hearth should be 36" x 36". I want to use a one piece bluestone. How thick it needs to be?