ᐅ Connect the vapor retarder and cover it with drywall.

Hello everyone,

We are currently installing insulation and drywall on the ground floor of our build. We may have overestimated our abilities a bit and now have a few questions.

We’re particularly concerned about how to connect the vapor retarder to the knee wall or the sole plate.
Our assembly is as follows (our part):
- 200mm (8 inches) rafters with 200mm (8 inches) cavity insulation
- Vapor retarder
- 60mm (2.5 inches) battens with 60mm (2.5 inches) insulation below rafters
- 12.5mm (0.5 inch) drywall boards

My idea was to connect the vapor retarder directly to the plastered masonry to create a clean seal. However, as hopefully visible in the picture, the sole plate and the aerated concrete block do not align flush. There is a small "projection" of 4-5cm (1.5-2 inches). On top of this is a black membrane (rubber-like, roofing membrane?). I have marked this in the other picture.

Here are my questions:
- Where exactly should I fix the vapor retarder in this case? To the sole plate or should I extend it onto the masonry? In my opinion, it should be connected to the masonry.
- How do I attach the drywall boards in this situation? In the attached image, you can see that the drywall would then meet the sole plate on the slope rather than the masonry, which would cover the sealed vapor retarder.

Thanks for any help!

Actually, the support beams at the base are usually built up with boards by the plasterer so that they are level...