OSB 3 instead of Ply

[BB78]

I've insulated under my ground floor suspended timber floor & now need to board over mostly to raise the floor back to the level it was at before, the boards will be laid on top of the 22mm P5 T&G floor and under Tarkett sheet vinyl which I'm re-laying. It is an open plan kitchen/living room but most of the kitchen area has already been covered in 2 layers of 5.5mm ply (re-using what I already had.)
Everything I've read says to use exterior/marine ply but at £30 a sheet it's expensive for what I want it for, can I use 11mm OSB 3 Sterling Board instead? It says it's "for structural use in load bearing humid conditions" (not that it should get wet being under the vinyl) & is suitable for flooring plus it's half the price of 12mm ply.

 

[ree]

Any chance of you doing a simple scanned sketch showing:

Section views of what is existing and what you propose in the kitchen and the adjacent room?

Is the sheet vinyl going to flow thro in one piece into both rooms? It comes in 3m, 4, & 5m widths. Best laid without any kit units in place.

How do you propose to transition from the living room into the kitchen - the line where the "different" floors meet?

 

[BB78]

Very quick sketch:
The shaded area is where I've already laid 2 layers of 5.5mm ply.
The dotted line is where the 2 pieces of vinyl meet, not joined just butted up to each other.

Transition from living room area to kitchen area - there isn't one.
'The line where the different floors meet' - if you mean where the 2 layers of ply will meet the osb I was just going to lay them next to each other.
The vinyl is already cut and been laid for a few years, it's only been taken up so I could insulate under the floor & the osb or ply is going under the vinyl as a final draft proofing measure, to level out the odd 1 or 2mm difference between board joints but mainly just to raise the floor back up to where it was before otherwise the door & plinths will have (too) big gaps under them.

 

[BB78]

Problem solved. Unearthed a builders merchant I never knew existed that can do 8x4 12mm WBP ply for £19 a sheet including the VAT & they deliver locally for free. Jobs a goodun, order placed.