I thought I needed an airspace in the hearth, like against the combustible wall, but if they say the "open faced sandwich" of plywood, cement board, mortar, and tile is sufficient, then I believe that.
Very nice! One thing puzzles me though. If backer board and tiles are sufficient protection for the framing of the raised hearth, why not just remove the floorboards in the area and replace with backer board and tiles?
Did you ever grow anything in the garden of your mind? - Fred Rogers. Tiny ad: