Building with or without a basement in Southern Germany - experiences?

ypg, I think he assumes that in such a HAR all the junk should find a place, besides the connections, heaters, and washing machine.

Probably But I was talking about three things: technology 5sqm, laundry 5sqm, storage 5sqm. I don't deny that one would still want a bigger closet for clothes, hobby items, or similar things like all the decorations or tools, but with good planning and many partition walls quite a lot is possible Above all, you have to want it that way! And the OP wants it. In that respect, I don't have to deny her that it can work if I were differently minded

But you are talking about net areas. Paths, windows, and supply lines are needed. Then the 15 m2 quickly become 25 m2. Our technical room is 16 m2. It only contains the building services and there is still space left for the drying rack. No space for storage or washing machine and dryer...