T&G floor prep for wet area with ufh

[ADAM T]

I've got a bathroom floor to tile, the area is appx 6 msq , will be fitting a wedi shower base former on raised section at one end of the room with a glass screen . Subfloor is t&g and will be fitting ufh , tiles are sheet mosaic on wedi and600x300 porcelain over remaining floor area.
If using waterproof boards (eg hardie backer etc) do i need to ply over the t&g first & if so what thickness of ply ?
Looking for opinions on the best way to prep the remaining floor area and recommended materials.

Any advice would be greatly appreciated , cheers

 

[tfs]

If it was me and I had the budget I would sheet over with cement board and then use decoupling mebrane to tile onto.

 

[tfs]

some peeps may not use them both, but I always think of the possibilty of the backer board moving with the substrate. solid T&G floor boards are the worst for expaning etc as timber expands most across the grain and expansion can be high due to number of planks spanning across the room.

With that in mind you may get away with using a mat straight over the floor boards if they are srewed solid down to floor, ensure gaps between each plank is no more than a few mm or you will need to sheet over first.