Subfloor

[Scudders]

Hi all,
I am tiling the bathroom floor and need some advice on sub floors.
the original floorboards are in very poor condition due to a hundred years of them being taken up to upgrade plumbing, electrics etc so I am starting with new from the joists.
I am installing underfloor heating with tiles over the top. I have 10mm backing boards already so my question is which subfloor shall I lay to put the backer boards over?
I thought about 22mm t&g then 9mm ply but this seems overkill with the 10mm backer boards.
any advice would be appreciated .
cheers, ian

 

[Gazzer]

Strengthen your joist with extra noggins then screw 18mm ply...22mm if you have the room to the joists at 200mm centres , use could quality screws to really pull it all together .
Over lay with the backer boards, install UFH and self level over , then you can tile.

 

[Rich Midge]

Spot on advice Sir Ramic!