ᐅ Vapor Barrier for Timber Beam Floor Ceiling

Hello everyone,

I have a question regarding a wooden beam ceiling and a vapor barrier.
I have a new wooden beam ceiling with the following structure:
Upper floor living area
- Cement screed
- Screed membrane
- Impact sound insulation panels
- PE foil
- OSB board 25 mm (1 inch)
Then the wooden beams.

Ground floor living area
- 180 mm (7 inches) compressed mineral wool between the joists
- Fermacell boards 10 mm (0.4 inch)

Now my question is: Do I need a vapor barrier above the Fermacell boards?

I would appreciate any answers.
Thanks, Nils

Hello Susanne,
First of all, thanks for your reply. Yes, the fermacell board is the ceiling of the ground floor. But could there be an issue since the fermacell has a lower SD-value than the OSB board, or is it not relevant because both rooms are heated? That is, the children's room and study on the ground floor, and the bedroom upstairs.
Regards, Nils

Here is the structure.

Hi Nils,

Exactly, if there are heated rooms both below and above, there is no significant temperature gradient, so no moisture transfer occurs through the building component...

Regards

Susanne