New extention with chipboard flooring, bathroom q's

[tfish]

The bathroom is currently bare stud walls and chipboard flooring. I plan to put 12mm Hardi BB on the studs... i want the floor sorted before i put the boards up as ill get a tighter fit with boards sitting on the floor rather than cutting the floor to fit around the boards...

What do i put on the floor to cover the chipboard? I was thinking plywood but do i need a special kind and what thickness?

Fix every 200mm? but with screws or tacks?

It going to be a normal batroom with tiled walls and floors no wet room

 

[tictic]

what size of area(m2) is it..?
joist spans..?
how much traffic will be going over the floor area..?

i ask as you could overboard with 6mm backerboaord or Xmm wbp ply or just lift and replace with Xmm wbp ply.

and what type/size of tiles are planning on fixing.?

 

[jctilingservices]

i was gonna ask the same questions as TicTic has just added, so now io wont bother

i will just add, i never tack boards, they are always screwed.