Marmox Boards Advvice

[SJPurdy]

I thought that the minimum thickness for overlaying a timber (chipboard or t&g) floor was 10mm if using the insulation type tile-backer boards (Wedi, Marmox and etc.), so I would recommend checking the manufacturer's spec to make sure before proceeding.

 

[AliGage]

The floor would need to be deflection free regardless. The thickness of insulation board only makes a difference to the insulation property value.
10mm I prefer on concrete floors but with timber 6mm is fine.

But regardless the floor needs to be deflection free.