Bathroom flooring OSB, Fermacell shower waterproofing

Hi, I bought a house from 1907.
Regarding the bathroom, I am not sure: we leveled the wooden beams on the floor (1st floor) and directly on top of that will be the OSB boards and then possibly Fermacell. Up to this point without foil or similar, and then I don't know if a shower sealing (Elefantenhaut) is enough to make everything 100% watertight. Thanks for helpful tips

Hello,

are you sure about it? Bathroom on a wooden beam ceiling, especially the floor construction, requires thorough planning and precise execution.
I would have the waterproofing done by a professional, for us a tiler. In our case, a decoupling mat from Schlüter was glued onto the dry screed, which absorbs the vibrations of the wooden beam ceiling and also functions as waterproofing.
The remaining waterproofing then with a sealing set from Ottoflex - sealing tape along the wall connections and shower tray including internal and external corners, sealing membrane in the shower and wash area, liquid waterproofing under the shower tray.

Good luck!