Ceiling construction with exposed beams - who has experience with that?

Hello everyone,
we need your help again with our renovation project (conversion of the barn into living space). During the summer holidays, we will be working on the ceiling. Here is a brief description:

We are only renovating the ground floor. Upstairs, the ceiling should only be walkable with rough-sawn boards. We have now planned the construction as follows.

Old wooden beams remain visible from below. On top of them, plasterboard panels will be installed from above. These are screwed onto OSB boards for stability. Then KVH beams will be placed on top again. The space in between will be insulated with Isover compressed fleece. And then the rough-sawn boards will be installed on top. Our question is, what do you think about this construction? Would you include a foil? If yes, where? What else should we definitely consider? In the bathroom and guest WC, of course, use moisture-resistant plasterboard panels.

We have already obtained an offer. The scope of services is as follows:
Cover existing beam layer with 12mm plasterboard panels, 22 mm OSB boards as vapor barrier including sealing and attach plasterboard to the OSB. Install a beam layer made of KVH 6 x 20cm perpendicular to the existing beam layer and insulate with 20 cm compressed fleece 032. Deliver and install 24mm rough-sawn boards on the new beam layer.

Thank you very much in advance for your help!

Can't anyone say something about this? :- )

Gypsum board between the two layers of beams, so at least subjected to compressive load from the dead weight of whatever is on top – I can understand if that leaves someone speechless ;-)

how should it be done better? First put OSB on top and then attach drywall between the beams from below?

Specialized topics like which vapor barrier goes where are absolutely not my area of expertise, so I cannot suggest an exact structure. However, I would not subject drywall to pressure load. In that respect, you understood me correctly, remove it from the load path between the upper and lower construction. Accordingly, only into the intermediate fields, yes.

Thank you for the response.

Hmm ... that doesn’t make things any better now. The extra effort of installing the drywall from below and constantly cutting it to fit (the beams are, of course, anything but straight) is obviously enormous. I’m not saying that you are completely wrong, I can absolutely understand the reasoning, but what surprises me is that I had 2 master craftsmen on site (who have a high reputation regionally) and both offered the approach I described.

That really makes me suspicious now. Maybe an expert in this field will read this post and can share their opinion.