Originally Posted by
Hondaman
Chances are you have a subfloor with an underlayment on top of it. You will remove the current flooring (carpet, vinyl, etc) and then remove the underlayment. The underlayment is usually a chip/particle board. Beneath it, there should be a plywood subfloor. You would put your cement board on that and fasten it accordingly, then tape and mud the cement board, then put your tile on top of that. As for the transition, you will need a piece of threshold trim. It is routered on half about 1/2 tall and will sit flush on the other side. It will make a nice transition.
Kind of looks like this.
Werd... Only problem is making sure the reducing strip matches the existing wood.... That is if the other room is wood. If not a piece of mable could work but it's usually used in bathrooms and some peep find marble to be tacky.