Diffusion-open underlayment, yes or no???

Hello,

...We just bought a house and want to fully convert the attic.

Is it supposed to be heated?

...When I stand in my attic now I look at the bare clay tiles do I now have to install a vapor-permeable underlay membrane then insulation + vapor barrier?

There is already a certain problem here. How is the vapor-permeable underlay membrane properly installed without integration of the roofing?

... Or can I also leave out the underlay membrane?

Hardly!

... If yes, does my insulation need air to the tile or press tightly against it?

Ventilation above the insulation is always an advantage, never a disadvantage!

...There are always very different opinions!

That’s true!

... Afterwards, drywall is to be installed because the room is to be inhabited.

A vapor barrier behind the drywall!

Best regards

Hello everyone!

I am facing the same problem, but part of my attic is finished and part is not. The builder of the house finished one part as follows. From outside to inside: roof tiles, battens (no counter battens) battens screwed inside onto the rafters, wooden boards for ventilation of the tiles, 10 cm of cellulose wool, wooden boards, 2 cm of Herathan (rigid foam board), 4 cm of Heraklith. Since I retrofitted a roof window in this area, I was able to inspect the construction and I was surprised that the entire insulation is dry, and it is also relatively cool in the finished area at 30 degrees outside temperature. Now my question: I would like to also attach battens on the rafters on the outside, then an OSB board for ventilating the tiles, and after that 18 cm of compressed insulation and a vapor barrier. Is that possible with OSB boards or are boards better because the joints are not 100% sealed for the circulation of the insulation?