I am starting with a 3/4" tg plywood subfloor. I will be installing 3/4" hardwood floors. For the bathrooms I want to install 3/8" travertine, with a 1/4" wonderboard underlayment. Considering the two layers of thinset, will I be close to having the top of the hardwood and travertine flush?

You'll be close. Do the wood floor first, and then tile putting enough thinset to bring it up flush.

Yes, that would leave you very close to being dead on, but...

1)stone installations require a double layer of plywood prior to the cement board being installed

2)your joist structure to support stone needs to be twice as rigid as the minimum for code compliance. More often than not, joists need to be either sistered to increase rigidity or a supporting wall/post & beam need to be installed to reduce the length of the unsupported span of the joists.

So, in order to be flush, you can either go with things as they and use any one of the many ceramics that mimic travertine, or, you can do some creative carpentry to your bath...

You would start by removing the subfloor in the bath. Then attach 2x's to either side of the joists, 3/4" below the surface of the joists. Then you install the 3/4" plywood subflooring between the joists, resting on the 2x cleats that have improved the defection of the joists. You now have 1.5" to play with. Next, you can install a second layer of plywood that crosses over everything. This layer gets fastened to the sunken subfloor only. Then you can install your cement board and stone. As another option, instead of a 1/4" backer would be to use Ditra membrane. The choice being with the 1/4" cbu, you will be up to 1/8" proud of the hardwood, with the Ditra, you would be about 1/16" shy of the hardwood, which can easily be made up with your thinset.

If you have access from below, you can install teh plywood from below and then install the 2x cleats along the sides of the joists from below. In either case, there exists the possibility of plumbing or electrical wiring getting in the way. They are an annoyance, but can be handled as needed.


Last option would be to add 1/2" plywood to the subfloor in the bathroom and then use Noble CIS membrane which is only 1/16" thick installed. Next, install a marble saddle in the doorway. You would still need to deal with the joist structure. If you are lucky, and the baths are stacked, you might have a short enough span in at least one of the baths.

What's the joist size, spacing and span?

The joists are 2x12, 16"oc and the span is 11'6". It does go over a 1/2 bath below. Since it is a second bath I may go with the tile suggestion. The master bath will be an addition to the second floor so I can start from scratch on the floor joists for that one.

Thanks for your help.