Requires approval? Connecting 2 apartments into a maisonette

Hello everyone!

We have been offered a nice three-window house. To make it interesting for us, we would have to connect the ground floor and first floor with an additional staircase to create a maisonette. My concern: In the attic there is a small rented apartment which, in my opinion, only has one escape route via the main staircase. I hope that the existing building protection applies here, but I might jeopardize it with the planned conversion. Since we are currently still in the phase of "is it even worth taking a look at the whole thing/getting a building survey/an architect involved," it would be great if someone could help me out. Many thanks in advance!

What do you want? Keep the apartment and expand the ground floor with half of the upper floor? A house plan would be necessary to be able to say anything at all.

If not even monument or ensemble protection stands in the way, I see at least one elaborate intervention in the statics.

If not even monument or ensemble protection stands in the way, I see at least one elaborate intervention in the statics.

To claim something like that, one should at least know one - just one - detail - as said, it is simply just throwing out rare eventualities. Completely out of the question.

To claim something like that, one should at least know one - just one - detail

We know two, those are at least one ;-) 1. the creation of a ceiling opening the size of a stairwell is planned => structural intervention, not trivial, certainly; 2. the term "Dreifensterhaus" was mentioned (that is a house type usually assigned architectural-historical significance and commonly found in closed development) => at least the initial suspicion of possible ensemble protection should be examined before assuming how to proceed with an ordinary used house.