ᐅ Vapor retarder on wood beam ceiling before plaster and screed?

Hello forum,

Our windows will arrive soon, and the interior work is about to begin.

My question is whether I should install the insulation of the wooden beam ceiling before or after the plaster and screed?

Structure from top to bottom:
Cold attic
OSB boards
240mm (9.5 inches) collar beam
240mm (9.5 inches) insulation batt
Vapor retarder
Battens
Drywall/Fermacell

Thank you

What does the site manager say about this? If the vapor barrier is not yet installed, all the moisture from the plaster and screed will move into the attic and can cause mold there if the moisture is not removed. It also depends on how the attic is ventilated. Are vapor barriers often covered with plaster and therefore necessarily installed before plastering?

Somehow, I ended up in the wrong forum; this should actually be in the insulation section.

The site manager says it goes on before the plaster, and then it will be embedded in the plaster.

I have only read a little about this topic so far, which has made me uncertain. You read that there is too much moisture for the vapor retarder to handle, etc.

We have an "urban villa," and the external thermal insulation composite system (ETICS) is still missing. It is supposed to be installed in the upper third of the house due to the cold temperatures.

In other words, there is a gap between the masonry and the roof structure.

We installed it before the plastering, precisely for the reason that the membrane is then embedded in the plaster at the edges.

Vapor Barrier Before Plaster and Screed
Vapor Retarder After Plaster and Screed