You want to build an extension opposite the old annex (to the living room, on the left side of the plan). The bedroom will be located in the old hallway and the old staircase, with a load-bearing wall being demolished in the process. The staircase will be placed in the old corridor, and the stairs will make a bend approximately at the chimney, which is no longer shown. A genuine amateur drawing with a set square on paper would be more useful for the understanding of all parties involved than you struggling awkwardly with a drawing program.
I correct: of course you don’t have to renovate the entire house. But an extension must comply with the new energy standards. And it’s worth checking everything.
No, everything must be subjected to the current standards, since the scope of the measures alone will legally create a new construction year. Demolition of an entire corner of the original building, insertion of a new ceiling in the current staircase, demolition of the ceiling in the corridor for a new staircase. We are clearly talking about a new chassis number here, even if large parts of the walls remain, and economically a lot of money. Where in NW are you located? ( is in Bad Münstereifel and might have a rough estimate of how far 200k would be missed just for the shell here?). Roughly, I would say you would build more cheaply new. The existing building will, to put it nicely, “not gain in market value” through the proposed measures.