ᐅ Properly Installing the Airtightness Layer

Good morning,

I am trying to figure out where I can connect my airtight vapor control membrane on the floor. In the first photo, you can see a cross beam between the rafters. Unfortunately, it does not seem to rest on the masonry. Since I can reach underneath there, that’s where my problem lies. How can I create an airtight layer there after insulation? In the second photo, you can see the current situation. The insulation can of course be removed again.

I hope you can help me.

Best regards,
Jens Kaufmann

In the first photo, you can see pieces of fiberglass insulation, with a ventilation grille behind them. You can basically look outside through it.