Insulation of pitched roof if upper surface insulation already exists

Hello everyone. I have the following question. A few years ago we bought a prefabricated house. It has a ground floor and an attic as living space. Above that is the pitched roof at about standing height. The insulation is currently installed on the ceiling of the attic. The attic space is not insulated, it only has a foil under the tiles (presumably a dust protection). I now want to lay OSB panels on the attic floor. For this, I plan to install battens to allow air circulation under the panels for the insulation. When checking the structure of the insulation, I came across the following. The ceiling of the attic is plasterboard, above that follows a vapor barrier (I assume, as it is metallic-coated paper) and on top lies the insulation wool. Now I am wondering whether I can insulate the attic and, if so, what the structure would be and how to connect to the vapor barrier? Do I have to open and fold up the roof insulation and barrier for this? I hope my explanations are understandable. Thank you in advance for your answers.

The fact that you want to lay the OSB boards with a gap to the insulation is already sensible. Nevertheless, I would leave a few larger gaps at the boards so that the air can really circulate.

I consider your plan to be critical. The attic would then be insulated but still unheated. Sealed all around with foil, so no air circulation. Logically, the air will stagnate there and very likely become a problem at some point. You would have to design it open to the upper floor, but I would think carefully about opening an existing insulation layer. From the way it sounds, it is still very easy to possibly renew or reinforce the insulation. Something I would keep open.

Is it about the additional storage space?

Hello Garfunkel.

Yes, that's right. Additional storage space is to be created. Currently, the floor is hot in summer but not frost-free in winter. So everything placed there becomes damp and moist.

I may need to add that there are 3 ventilation holes on each gable wall for the attic ventilation. If the attic is insulated, I would definitely have to close these as well.