OSB or tongue and groove boards for flooring in an expandable attic?

Hello everyone, I have now covered the first half of the attic with tongue and groove boarding. I now want to additionally install insulation between the rafters at the top so that it doesn't get too cold/hot. But I'm still having trouble with the vapor barrier. I have attached one, but I haven't strictly ensured that it is 100% sealed to all other components. For me, it is only meant to prevent the insulation from being exposed. Is that okay? Or does the vapor barrier still have to be perfect even in an attic that isn't completely airtight? Thanks and regards

Better try to glue the corners as well. So that it is sealed. I'm not a carpenter/joiner, but I did it with someone from the family. He said it has to be sealed. He also said it has to be a brake, not a lock.

If you have a vapor barrier in the ceiling between floors, that would not be a problem. Without an additional vapor barrier, your insulation could become damp. To answer this, one should consider the purpose of a vapor barrier or vapor retarder.

The goal is to protect the insulation from moisture in the indoor air. Dust protection or the structural separation from the room side is a secondary effect.

So
- Do you already have a vapor retarder in the ceiling between floors? Common in bungalows with cold roofs.
- Does the roof have a diffusion-open underlay beneath the roof covering? This prevents rain but allows water vapor to pass outside.

Hello and thank you for the feedback. I can answer both questions here with yes. There is a vapor barrier at the upper floor ceiling (gable roof with a cold attic). And there is a diffusion-open underlay beneath the roofing.

Hi!
So, how did you solve the issue now?

Hi, haven't done anything yet. I'm still not sure exactly what I should do now :)