Ply Vs Osb

[SJPurdy]

I've mentioned tile backer boards but I think it's gonna be ply or osb

Why?
It appears to me (from your post) that you have a wood floor (probably t&g so maybe not flat enough to fix ditra directly) and you are going to fix OSB or Ply (Ply recommended by BS, OSB not as far as I am aware) to make the floor flat so you can fix Ditra to it.
I am really confused as to why you want to continue to consider the unapproved, untested OSB.
Ply is the recommended wood overlay to strengthen a floor if required. There are better tile backer board overlays in my opinion which have been tested to work and if height is an issue then as stated by others the floor could be removed and replaced with eg Hardiefloor.
Then also what is the reason for wanting to use Ditra in addition (there are some valid reasons but not required in every case in my opinion.

 

[Tile Shop]

QED.

Wasn't that a science show back in the 90's?

 

[Kyle Knowles]

No I'm just asking opinions on the subject the builder was asking me what options I can come up with so I posted on here from what I've had back from schluter it's gonna be ply goin down and the reason for ditra is the customer has stipulated the use of Ditra to the builder probably bin on the Internet and bin reading what the customer wants they get

 

[Time's Ran Out]

Ply and 100% Ditra is the way to go - imo.
We got there.