OSB panels in the pitched roof

But we plan to insulate the rafters under the roof tiles. But not the attic as living space.

Is that a problem?

No, that is not a problem but actually the better solution, overall!

Why the better solution?

I thought the best solution regarding energy efficiency is to insulate both the roof and the attic?

Hello "Marchonisch",
the answer to your last comment here as a metaphor:
If you are anxious, you can wear suspenders over a belt as well. Then the pants certainly won’t slip!
Normally, at least according to experience, a belt alone is sufficient.
More efficient in terms of lower heating costs is certainly the thermal insulation under the top floor ceiling. Because otherwise you are heating the attic unnecessarily.
But ultimately that is up to you, both insulation approaches are permissible, both variants are used in practice!!

And the OSB boards can be installed regardless of whether the roof or attic is insulated. Or of course, if I insulate both?

Otherwise, there is no reasonable reason why wood-based panels should not be installed in a dry room (meaning: it does not rain in here and there is no condensation on the wood-based panel surface).

This question has already been answered. Under non-climatized conditions, wood-based panels can warp slightly, but if they are nailed to wooden battens or glued tongue and groove and used only as a subfloor in a rarely used attic (thus not a living space), this is insignificant.

KlaRa I am an amateur. Only my professional colleague, who is a carpenter by trade, said that on our cold attic - the ceiling floor is insulated, not the roof - for the covering he would not want OSB but rather spruce tongue and groove boards nailed board to board, so that the mineral wool underneath is not sealed so hermetically. It’s not more expensive either. Karsten