Designing Kitchens and Bathrooms - Question on installing bathroom floor

I just finished gutting out my bath and am in the process of laying down 3/4" Plywood on top of 80 year-old 3/4" Plank sub floor. I wanted to install 1/4" Wonderboard on top of the plywood and then 1/4" tile on top of that. A couple questions:

1) Would I install the Tub on the Plywood or the wonderboard?

2) Is this too many layers? (Right now, the sub floor is 3/4" lower than the hard wood outside of the bathroom, with the plywood it is level. Add a 1/4" wonderboard, 1/4" Tile and whatever the thinset adds and I am looking at at least a half inch higher than the hardwood outside the bathroom)

3)Is there a thinner water resistant substitute I can lay down instead of the wonderboard?

Thanks a million!

Hi,

It doesn't matter whether the tub goes on the plywood or on the backer board.

You probably could have used a thinner plywood, but since you've started, go for it. The 1/2 in. can be accommodated by a hardwood reducer strip. It'll look just fine.

John

http://www.johnbridge.com