Replacing particle board underlayment and building up floor height to lay tile
Plywood would be a very good choice. You should consult the ditra literature for your particular joist spacing, however, generally the bare minimum thickness for plywood/T&amp;G subfloor under ditra is 5/8". Plywood in general adds more strength to a subfloor than cement board, and given that you are going over it with ditra, it makes more sense to add plywood than it does to add cement board. If you are looking to come up around 1" you could use 1/2" or 5/8" ply + 1/8" ditra + 1/4" tile would get you pretty close to 1". In the context of tile, you want as stiff of a subfloor as you can get. Ditra is a great product and I have used it over major structural joints with no cracking of grout or loosening of tiles.