I have an upstairs bathroom that needs to be retiled. Unfortunately the original install was just tile over plywood, which was level with the rest of the flooring upstairs -- 3/8" engineered hardwood. The mortar on the old floor crumbled for obvious reasons and when I went to remove it the tiles just lifted up off the plywood. And they were 6" tiles; I want to redo it with 6x24 faux wood ceramic tiles.

So I am looking at ditra (or ditra-heat) underlayments. They have a certain thickness, and there's a mortar under and above the ditra. I see the trowel sizes in the instructions, but nowhere does it say exactly how much height the ditra (or ditra heat) adds. This might be obvious but I'm not experienced at tiling.

I want to minimize the added height to the new floor to keep it as close to level with the 3/8" engineered wood in the rest of the house. I'd like to add heat too if possible -- I realize that's contradictory but before I rule it out I want to know how much height it adds.

So can somebody tell me how much height, in practice, is added by ditra and ditra heat underlayments? Thanks in advance!