ᐅ Drywall before the screed?!

Hello everyone,

In my new build, I have a wooden beam ceiling that I have already insulated (since the attic is not used as living space) and installed a vapor retarder.
Should I now screw the drywall sheets to the ceiling before plastering? And after that, install the underfloor heating and then the screed?

I am concerned about moisture affecting the drywall sheets and would prefer to do this after the screed has dried.
However, the plasterer would obviously prefer to be able to plaster directly onto the boards.

Thank you very much for your opinions.

How is the vapor barrier connected to the masonry? In my opinion, plastering needs to be done first, then the screed, and finally (preferably after drying) the ceiling inside is covered (gypsum board).

The vapor barrier is attached to the masonry with sealing adhesive. So, everything is really sealed tight to the top.
Yes, that’s exactly the sequence I had in mind as well.

It is often done differently to achieve a clean finish with the plaster... which then just tends to mold.
I would also plaster first, then pour the screed, and finally apply the plasterboard.

The correct sequence has already been mentioned. Before the plasterers come in, you should carefully trim the protruding vapor barrier just beneath the sealing adhesive so that the area where the plaster will be applied to the membrane is as small as possible. Otherwise, the plaster in that area may detach again after drying.