Prepping floor for tiling - options?

[NickyBoy15]

I’m looking for some advice for preparing the floor for tiling in an upstairs ensuite. Currently, the flooring is pine floorboards which are partly taken up at the moment for cabling and piping. The righthand stud wall is on the current floorboards between the joists.

I’ve got some Schlüter-DITRA-HEAT-DUO-PS peel and stick uncoupling membrane I’m running the underfloor heating cables in before tiling. In case it matters, tiles are going to be 1000x1000mm.

I’m thinking the options are -

Option 1 - Take up the existing floorboards (leaving the 150mm on the right the wall is built on), replace with marine ply and try to match the height of the remaining boards, lay the uncoupling membrane, seal and tile.

Option 2 - Tighten the exiting floorboards as best as I can filling the gaps *some how*, lay the uncoupling membrane, seal and tile.

Option 3 - Same as above but with 6mm backer boards over existing floorboards.

I’d appreciate any advice you can give. I want to do the job properly without making extra work for myself.

 

[Wayners]

Not my area but.
I used moisture-resistant chipboard and glued joints.
Tiled on that with correct adhesive.
Been down 19 years.
It's the same width as floorboards

 

[simplesteve]

My choice would be option 3. You can’t go wrong with 6mm H.B. on the floor.
( I know it’s highly personal, but 1M sq tiles on that floor are way too big )