OSB panels in the pitched roof

Yes, that is also correct, Karsten. If faults occur in the vapor barrier, penetrating moisture can escape upwards through the gaps of the spruce boards. OSB is too dense for that.

We have installed ESB boards. These are, unlike OSB boards, vapor-permeable. Just like tongue and groove boards, but easier and faster to install. Looks great too.

Hello,

what is it actually like with an insulated reinforced concrete ceiling?
Can I lay the OSB boards here seamlessly, or can there also be mold problems?

Is the ceiling fresh? Reinforced concrete is rather not vapor permeable. That means basically it works. However, if the attic is not heated, you desperately need insulation!

Hello,

the attic is a cold roof, therefore it will not be heated. As can be seen at the passage of the roof hatch, there is about 25cm of insulation on the concrete ceiling. Did you mean this insulation?

Yes, exactly. So in my opinion, there is nothing against it. The concrete ceiling already serves as a vapor barrier.