According to the floor area ratio, only 138 m² is possible - 2 floors - Help :)

.. we are currently planning this with the architect

Then I am either now wondering about this thread or about this answer.

Three houses come to mind spontaneously that stand on old cellars. Only for one of them does the cellar fit the house.

It works. The question is what it costs

It’s not a must - just seemed to make sense at first glance ;)

Then I am now either wondering about this thread or about this answer.

... I am looking for inspirations and experiences - because I don't want to be completely unprepared - the appointment is not until 14 days from now

The 139 m² floor area ratio is of course really tight. Currently, 80 sqm are already used by the single-story building. The attic floor should therefore only have 59 sqm .. external walls. It is therefore necessary to determine what is stipulated for you: The development plan can stipulate that the areas of living rooms on other floors, including the stairwells belonging to them and including their enclosing walls, are to be counted wholly or partially or, exceptionally, not counted at all.

... I am looking for inspirations and experiences - because I don’t want to be completely unprepared - the appointment is only in 14 days

But that only works with definite information. If you can’t provide that.. it can only be a little chit-chat session here. That’s all it is here at the moment anyway.

.. then go ahead and provide the site plan ... as already suggested.