Floor plan optimization for a semi-detached house of 150-160m² on a 360m² plot in a new development area

We are currently comparing a regional general contractor, solid construction, and 3 prefabricated house providers. KFW 55 or better, depending on the specific offers. Photovoltaics would be a nice extra. We'll see...

When the two then move upstairs, they are old enough to sleep through the night or to manage stairs alone at night

I have a 6-year-old at home.
The way he wanders through the apartment at night when he has to go to the bathroom, it will take a few more years before he could manage stairs.
It will only take 2 more years until both children are old enough to sleep upstairs, until child 1 hits puberty and chats with friends on weekdays until 11 pm and then comes up with the idea "oh, I still have to shower. And then blow-dry my hair." You’re sure to be annoyed if you want to sleep.
3 years later they come home drunk from the town wine festival and have to go down the stairs in that state when they want to go to the bathroom.
A living floor without a toilet would be a deal breaker for me.
Otherwise, I’m not a fan of "But think about the resale value!", but here please bear in mind that many 4-person families will immediately rule out your house.

Thank you for your contribution. I really enjoyed the horror scenarios you described. Your description is certainly not far from the reality of many families. I have experienced it myself that people are considerate of each other (e.g., not showering at night) and also intend to pass this on. However, if one day we dream of having a bathroom in the attic, we will at least have the corresponding pipes installed directly. And so that they end up in a sensible place, here is a floor plan of the attic with a bathroom (even though we probably won't implement it right away...).

The toilet may fit reasonably well into the floor plan, but you do realize that besides water (simple!), you will also need a wastewater pipe with a slope for it, right? Currently, it comes out in your bedroom as at least a 15x15 cm vertical wall section (nighttime business that can keep you awake...), which will neatly split your wardrobe front in half. Or you have quite a hanging (at least 30 cm down from the ceiling) in the hallway of the upper floor until you reach the pre-wall installation of the WC in the storage room. And you should definitely plan these drainage channels as well, if at all!

Alternatively, something like this would be more conceivable - you can still use it as a storage room at the moment, for example for toys. And if you haven't planned the attic yet, it would be conceivable to build this room only about 2.3 m high and to create a level on top that could be used as a sleeping loft from one of the two rooms.

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Drainage is then done below in the bathroom.

I think it’s great that you are deviating from the classic terraced/semi-detached house floor plan. What I still don’t like, however, is the living room. It’s stuck to the edge and feels uncomfortable. How did you envision the staircase that extends into that space? I also don’t find ideal that you have to walk through the opening and then maneuver around the kitchen island. Upstairs, I’m still not happy with the new bathroom layout. Everything is very cramped, just so the toilet can be hidden.

I sketched another idea for you. The staircase is shifted a bit towards the entrance side. There is space for a wardrobe in front of the stairs and additional storage under the clad staircase. I would clad the staircase extending into the living room and use it as a built-in cupboard. Preferably also with a decorative opening and lighting. Upstairs, the slightly shifted staircase would also work well. You have to imagine that yourself now.