My answer has become somewhat futuristic
Width of the version 6.50 meters.
I haven't calculated the total area anymore.
I assume that the BU proposal will be built anyway. So it should simply be seen as an enrichment for the forum






Why like this? I think the original poster has dealt with an integrated staircase and simply wants a large open space.
In the attic, there is a gallery for hobbies and playing. Later it can be used as an office, parents can move upstairs.
Edit: Shaft in the NE bathroom and upwards. I deleted it in between and due to lack of time the doors are naturally also missing – but it's only to be seen as a sketch anyway.