I'm reflooring both my kitchen and the adjoining rooms. The kitchen will be tile and the Living Room/Dining Room will be engineered hardwood. I'm going down to the joists in the kitchen because the existing subfloor is damaged (and I may need to reinforce the supports to put floor tile and granite countertops), but I'm assuming I'll need a 5/8" plywood subfloor laid over the joists. I assume the kitchen will then have 1/2" wonderboard, 1/4" of radiant heat, and 1/2" of tile totalling about a 1 1/4" height off the subfloor for the kitchen. The DR/LR will have 1/16" of radiant heat plus 1/2" of engineered hardwood. So that's at least a 11/16" difference in floor height.
I know that there are transitions available to go from one floor height to another, but that seems like a lot of height difference (and I'm a klutz) so here's the question: Can I lay down another 3/4" layer of plywood over my existing LR/DR subfloor before putting in the radiant heat/engineered hardwood and thus minimize the floor height differences? Is there something I'm missing or some better solution?