Plywood arrangement for bathroom subfloor

[jacoscar]

I have a bathroom under renovation; I’ll removing all existing floorboards and replace with 18mm plywood, which will then be over boarded with something like cement boards or similar before tanking and tiling.
I need 2 plywood sheets to cover the entire floor, which arrangement is better, A or B?
With A there are no unsupported sections so it seems better to me, although I might have to put screws close to the border of the sheets where they meet on the same joist

 

[Deluks]

B seems better for some reason, but use t&g plywood. Or you could add extra timber under where the joints are. Your diagram doesn't show struts or noggins.
An alternative would be to have a full board in the middle and a half board either side.

 

[jacoscar]

B seems better for some reason, but use t&g plywood. Or you could add extra timber under where the joints are. Your diagram doesn't show struts or noggins.
An alternative would be to have a full board in the middle and a half board either side.

I already have the two structural plywood boards. There are no noggins at the moment, in this house they were only in the bigger rooms (floorboard offcuts). Not really feasible to add them now as there are pipes. But could still add some timber at the top and bottom of each pair of joists, then screw the plywood to it

 

[Deluks]

Even a 4x2 on it's side, is better than nothing, just to support the joints.

 

[Deluks]

Just ensure no bounce at all in the floor if you're tiling. Screw every 200mm.

 

[stevie888]

B will provide easier cutting and handling of the boards. I'd just cut some strips of ply and screw and glue them to the free edge to support the second sheet.