We took up the concrete bed in the front entry and now want to lay new 16x16 travertine. We need to build the floor up and someone has suggested to use a sleeper floor.
1. When I look online to research most projects using the sleeper floor involve concrete slabs and trying to avoid moisture problems that occur if you try to combine wood and cement. Why would I use this option rather that just layering more wood on top of my old sub floor?
I have to assume that this is sitting on the main deck of the house and that the front entry was "carved out" of the surface of the main deck. How much are you trying to build up? How thick is your prep work (i.e. self-leveling concrete base for the new tile)
1. how deep and long are the floor joists under the front entryway?
2. are there cross-braces between the joists?
3. what are the centres for the joists?
4. how thick is the sub-floor?
5. take your 400lb line backer teen-aged son out to the front entry with you. Stand there and have him jump up and down. If you can feel him jump, your floor isn't strong enough to support Aunt Martha on your new tile floor. Time to beef it up. Alternatively, I had a little 15lb. Shih-tsu-Poddle mixed race dog that just walked at a pace that set up complimentary vibrations and when he walked you could feel him all over the house.
It is quite possible that you will need to return to the concrete bed that you so painstakingly took up. You have several issues: moisture that will come on snowy and rainy days; adequate support for your tiles even during dry periods where your structural wood is going to shrink slightly; The structure will have to be protected from that. The floor was that was there, how badly was it cracked? That will tell all. How thick was the concrete? If there was no cracks, the original builder knew what he was doing and you want to replicate what he did.
2. If I do use this method, how important is it to get the strips directly over the floor joist? Would I be redistributing weight to an unsupported part of the floor if my strips of wood don't sit on top of the floor joists?
Depending on how the floor is built, very important. see above.
3. Do I use adhesive to attach these strips or do I nail them into the floor joist below?
I would use adhesive and galvanized/stainless screws not nails.
4. Since my floor won't be solid...there will be an empty space between my old subfloor and the new sheets I use to build up the floor....won't my floor have some bounce to it? It doesn't seem like it will be stiff enough to support my tiles...won't they crack?
Yup! Your supporting structure must be designed to support the new tile floor. It may be worth your while to sister in supplemental joists between existing ones if there's too much bounce. My thinking is this: if there is any bounce put in cross braces. If there's still bounce, go back and either sister in new joists or space new ones between the old ones.
Let me explain. I had a house with a crawl space. The joists were 24" on centre and were 2 x 8s 12' long with a 1 1/2" notch taken out of each end. I ended up sistering in several joists to support ones that had split and supporting them with joist hangers. I then went back and put in bracing between each pair of joists and my floor went from a trampoline to strong and solid in a week's work.
Pictures would help too. Got sketchup? try giving us a drawing so we have a good idea of what you're trying to accomplish.