I am replacing a shower tray (1200mm x 800mm) with a new low profile
25mm high tray. The new tray recommends the floor should be 18mm marine ply. The current floor is 18mm chipboard and since some walls sit on top of this if I replace this floor with 18mm ply then the ends of the ply (200mm) will overhang the floor joists and would therefore seem to me to be more flexible than the current floor. This is a inset tray so has plasterboard walls on 3 sides so the ply will have to be exactly the same size as the shower tray. The current shower tray was raised up on 4x2 with 18mm chipboard on top for easy drainage but I have got round this drainage issue and need it as low as possible What do people think I should do as I am not sure how much difference there is in flexibility between the two materialsThanks