I'll be putting down ceramic tile in the kitchen/breakfast area first and following that in a couple months with hardwood flooring in the living, dining and entry. Initially I was going to lay everything over the OSB subfloor but now I'm leaning toward adding cement backerboard under the tile. If I lay the hardwood on top of the OSB, how do I handle the 3/8" height variation between the two types of floors? I'm new to hardwood flooring and don't know if there are trim pieces that will make this transition smoothly.

You could either use a thicker wood floor (that is costly) or just get an overlap reducer.

You could lay plywood of the desired thickness over the OSB to give any finished height you want.
If you don't care if there is a small difference in height, you can buy/make a transition strip at the interface edges to go from the wood height to the tile height.

I personally like floors that have the appearance of being all at the same level; but small changes are not uncommon and are perfectly acceptable; sometimes almost unavoidable in remodelling situations.

I realize this is a Wood Flooring message board but would someone weigh in on the need for backerboard under ceramic tile? What I can find on the subject is that it is recommended but not necessarily an absolute must. Laying the ceramic directly on the subfloor takes care of my height variation issues but will I suffer from a poor tile installation?

There is a very good tile message board (link attached) http://www.johnbridge.com/
Look through all the messages there for a good understanding of tile and tiling. These forks will help you do it "the right way"...

You will find that you need either the cement board or a product called Ditra. Cement board comes in 2 thicknesses - 1/2 or 1/4. Ditra is only 1/8 thick. It is easy to work with and may be your answer. I used it in 3 rooms I did and it worked great. The difference between wood and tile was about an eighth of an inch. Just add "T" moulding for the transition between the two.

Good luck,
Ken

Ditra is the way to go. It is foolish not to use the proper underlayment. Either Ditra or 1/4" backer board because the cost of replacing is much more than doing it right the first time.

Check out the John Bridge forum and buy his book. You need to make sure your subfloor is appropriate also.

Norm, installing tile directly over OSB is unacceptable, just forget that notion. If you want to keep the same heights use either a 1/4" cement backer board or what I prefer is 5/16" Durock brand CBU. Make sure to install the backerboard in a troweled bed of thinset and use Durock mesh tape over the CBU joints before tiling. How thick is the OSB and describe the joisting? 2x? , ? OC spacing, how far do they clear span? You have to be very careful installing tile correctly.

Thanks for all the input. The decision has been made not to cut corners but to use the backerboard under the ceramic tile. I'll tackle the floor height variations when I get to laying the hardwood.