This is my current project, a level entry, barrier free shower. Part of a complete bathroom remodel. The original floor had three layers of plywood. The original subfloor was pieced together 1/2", which led to the decision to remove all the plywood, back to the floor joists. The original plan called for sistering to the existing floor joists, however, once the flooring was off the joists were pretty rough. Ripped them out and installed new joists (notched out 1" for level entry shower) double layer 5/8 ply, in floor heating with slc. The shower was reframed, bulkhead added, clad in CBU, Kerdi drain and mud bed. Will be waterproofed with Kerdi, then tiled.