Flooring Tile - Subfloor for marble and ceramic - desperatly needing help

Hi folks,

It's my first time posting here although I have been reading the forum for a while. I desperately need help with issues described below. I will greatly appreciate any piece of advice.
I plan to put A) marble tiles in the bathroom (~50 sq.ft, rectangular shape) and B) porcelain tiles in the kitchen (~100 sq.ft., square shape).
First of all the status quo:
Relatively new house - 7 y.o., joists are 8x2 about 14-15'' apart supported at 11-12 feet, the floor is particle/chip board either 5/8 or 3/4 (not sure).
It is covered with 3/16 plywood (definitely not 1/4 - I measured it) and vinyl.
Elsewhere in the house I have 3/4 hardwood installed directly on the particle board and I would like the new flooring to be at the same level.
For the forementioned projects A) and B) I have already purchased some 1/4 RhinoBoards from Home Depot:
http://www.custombuildingproducts.com/ProductCatalog/SurfacePrep/Backerboards/OneQuarterInch_RhinoBoard.aspx?user=diy&lang=en
I was told that they are equivalent to 1/2 - 5/8 plywood and that I should be fine.
I plan to rip off the vinyl and then the 3/16 plywood that appears to be only stapled anyway. On the particle board I want to lay thin-set mortar and put 1/4 RhinoBoard, on top of that I will put thin-set mortar again and then poreclain or marble tiles respectively. This should allow me to ideally "meet the hardwood level (1/8 thin-set + 1/4 Rhino + 1/8 thin-set + 1/4 tile = 3/4 H/W)
Now the problem that I have is whether IT IS ENOUGH?
I am especially hesitant about the marble which is after all quite heavy but also soft and cracks easily.
What are the correct subfloor solutions for my projects A) and B)?
If I have to live with a reducer I will because the last thing that I want is cracked tiles. I am new to this kind of project therefore any help will be greatly appreciated.

Thanks
Adam

First off, that floor doesn't meet specs for marble, second, are you sure that you have particle board and not OSB, I doubt you have particle board as the original subfloor.:)

Yes, remove the vinyl and it's underlayment, 1/4" backerboard is fine, don't know what they meant by equal, it doesn't add any strength to a subfloor, it's just there for a backer for tile, set it with unmodified thinset with a 1/4" trowel.:)

Let's first see what you have for a subfloor, OSB looks like alot of small pieces of wood glued together.:)

Thanks Tileman
Regarding the subfloor you right on - it's an OSB - I should get the terminology straight first.
The support for joists is actually at 11 ft.
Also in the basement there is a 4 ft hallway going underneeth a half of the bathroom. That, I guess gives some support with 2x4s to the joists under the bath above at 7 ft., the remaining half is 11 ft.

Can you please elaborate a bit on the Rino board? What is it good for then? So Should I return it and get regular plywood instead and put tiles directly on plywood?

I wouldn't tile directly on plywood, the CBU is there for a backer for the tile, that's it, it doesn't add strength to the floor, if strength is needed, that's what the plywood is for.:)

Plywood strengthens a floor between the joist spacing, joists determine the overall flex in a floor.:)

Yes, but will 5/8 OSB and 1/4 Rino be sturdy enough for marble or should I add plywood between OSB and Rhino??

Thanks

I would add 1/2" plywood over the OSB, then the backerboard, also, that 11' span, is that getting the marble?:)

Yes - marble goes there.
Well, you're not making me happy with this 1/2 inch plywood...
I hoped to make it flush with hardwood

I wouldn't tile that floor with stone , 2x8s at 11ft. unsupported not strong enough, guess you really hate me now. :D

I guess I do..... grrrrr
Honestly, even if it is supported half way at 7ft?

If the span unsupported is 7' that is getting the stone, your fine.:)

You can not go more than 8' unsupported with 2x8s for stone.:)