Construction costs for a turnkey single-family house on a slope 2022

The basement apartment will be a massive loss-making venture despite subsidies and possible rental income.

Besides the loss from my point of view, also a loss of quality of life, because there is always a stranger nearby whom you have to consider and who can get on your nerves.

We would like to build a purist single-family house, where our aesthetic preferences probably come closest to the Bauhaus style (cubic, flat roof or monopitch roof, few frills, open spaces, window fronts to the south and east, possibly a roof terrace),

Does the development plan share your taste?

We prefer a turnkey solid prefabricated house, if possible with KfW40 standard, without smart home.

Does solid prefabricated house mean: wall panels made of porous bricks, expanded clay, ... ?

Thank you very much for the feedback! There is no development plan and no building envelope either. According to my research, no architectural regulations can therefore be made (especially since there are also flat roofs on the street). I would probably build with expanded clay aggregate (+ external thermal insulation system I assume for KfW40).

The granny flat is currently not for outsiders, but it will be rented out in the future. Can you explain the issue a bit for a layman like me? Why is the granny flat making a loss? Is it so much more expensive than "normal" living space?

I am very grateful for any tips!

You are building 70sqm. The cost is 2.5k/sqm + additional costs. So roughly 200k in costs. Since you don't want complete strangers that close in a single-family house, you rent out (too) cheaply to acquaintances.

With a rented granny flat, you effectively build a house without a basement again since the basement is used for the granny flat. This results in high costs (a residential basement is more expensive than a utility basement, you sometimes have to duplicate building services), additional parking spaces are required, and you always have someone on the property. On the other hand... you have to build a basement anyway on a hillside, so I am not as clearly against it as others. Without more detailed information, there is relatively little reliable information to be said.

There is no development plan and no building envelope. According to my research, no architectural regulations can therefore be made (especially since there are also flat roofs in the street)

None (building envelope) on paper. The building just has to "fit in". There are still distances to streets/boundaries/neighbors, etc., and if the building mass doesn't please "a nose" at the office, it will also be difficult. First do a budget check, then the house almost "designs" itself.