Hello,

I'm hoping some of you with experience with remodeling bathrooms can help me plan how to build my floor system to include a heated floor, ceramic tile, and doorless zero threshold shower with trench drain.

I am remodeling a small master bathroom. I removed all the floor and subfloor down to the joists in order to update plumbing and electric. Now its time to put in the new subfloor and floor. I removed two layers of what looked to be 5/8" plywood under carpet (nasty and lots of rot underneath), so I have roughly 1.25" available to be flush with the adjacent hardwood floor. There is a small shower that is about 36" square that I want to drain towards the bathroom into a trench style drain, zero threshold, such as the Proline Drain from QuickdrainUSA.com. Anyone have experience with these? I also want to include a heated floor such as Suntouch. Anyone have experience with these?

So my root question then is what to put under all of this...I will finish with large ceramic tiles, say 12" square. I have heard two schools of thought on this from various people I have asked and DIY books from the library:
1. One layer of 3/4" plywood, then cement board tile backer 1/4", then heated floor, then tile, and done - this should come close to flush with the hardwood floor adjacent
2. One layer of 1/2" plywood attached to joists, another layer of 1/2" plywood attached to first layer but not to joists, then cement board tile backer 1/4", then heated floor, then tile, and done - this will put me above the hardwood floor adjacent

Within the shower I would follow the manuf. instructions for the trench drain.

One more question - some of the existing 2x10 joists have damage from demolition - should I sister them at the top edge with a 2x6 to bridge the damaged areas, and glue/screw the new 2x6 to existing 2x10? Or is the plywood good enough to bridge these areas?

Your advice is appreciated! And don't assume I know anything, tell me everything I need to know...

Thanks!
DIY SG