Floor plan after the first planning meeting, 140m², 1.5 stories

The upstairs hallway is a dark hole without sun...

I’m coming back with harsh words, in my eyes it’s planning failure through and through.
(Orientation of the house on the plot not taken into account.)

- 27 sqm bedroom that are not really usable - not even 3 m wall for a wardrobe
- then mini kids’ room + slant (even if you first have to "work" for it :D)
- bathroom: hallway to the toilet becomes a torment
- upstairs hallway (already mentioned)
- washing machine next to the couch (soundproof wall or not...) .. technology in general
- to me it’s all too open: hallway/stairs/cooking/toilet/eating... --> you don’t even have peace in the living area. Front door --> stairs (you hear everything...)
- ???

What is actually the challenge that prevents you (or the woman) from creating a sensible floor plan with normal dimensions?

Why 45 cm walls? Use wooden studs, you get about 4 sqm downstairs, 2 sqm more upstairs, with identical dimensions and equivalent building envelope

We are still considering windows in the upper hallway above the stairs.

Dark room without daylight vs. some daylight through a window. I understand, that's a tough question, and the answer needs to be well considered... I don't understand why you are struggling so much. Regarding the comments here, you offer no arguments, just "Yes, hmm, you can see it one way or another, it's a matter of opinion and we like it...". You would also have liked the first floor plan, but only until you moved in. Just believe people who have already built / live in a house... Addendum: If 200 wrong-way drivers come at you, you should probably ask yourself whether you're driving the wrong way yourself!

And I grew up in a house with exactly such a hallway on the upper floor. And I always found it nice, I don't know it any other way.