Single-family house approx. 150 sqm floor plan - How to plan the staircase?

... and wouldn’t have to continue gathering the things he forgot in the evening with the phone flashlight to lay them out ).

Well, he really is a very sweet man, isn’t he? Cute!

Is he [emoji846]

I would raise the knee wall, make the roof pitch flatter, accordingly convey that the single-story nature is still guaranteed despite the captain's dormer. That gives more space on the upper floor. Then I would slightly normalize the size of the children's rooms on the upper floor. If I see that correctly, the dormer is in the NW? Then put the bathroom completely in it so that every family member benefits from the beautiful dormer. A slightly larger storage room on the upper floor can become the utility room, but only if it fits. If necessary, you can then combine storage and pantry downstairs and make them properly accessible via the hallway—the passage through the kitchen ruins the whole dormer feeling as well as the kitchen unit. There should also be a bit more space left for an office.

, I’m not quite sure what you mean down there. Can you make a sketch? Putting the bathroom in the middle at the top and shrinking the kids' rooms might possibly create a huge walk-in closet. I think that’s a bit of a waste. Or what did you mean?

What roof pitch and knee wall height could one approximately aim for without creating another full story? Although it shouldn't be too high either, as I don't find that very appealing in the exterior view... The children's rooms being a bit smaller is ok, but with the bathroom in the middle, they would actually be too small for me; we don't need that much dressing/parent sleeping area, and the children will "live" much more in their rooms later on...

, I’m not quite sure what you mean down below. Can you make a sketch? Putting the bathroom in the middle at the top and making the kids’ rooms smaller might possibly create a huge walk-in closet. I find that a bit wasteful. Or what did you mean?

Unfortunately, I don’t have time to sketch. I think there is still a lot of potential that could lead to a good result if you move the rooms around for a few days. While I was looking at the upper floor again, I realized that it is only 3 meters wide. So you can’t even place the bed under the slant. Therefore, the area under the sloping roof is wasted here. It therefore makes sense to rethink the stair position… possibly just mirroring it in the hallway is enough. In your example, kaho, you could make the walk-in closet into the bedroom with access from the walk-in closet. Behind the walk-in closet, under the slant, a storage room...

Dear OP @manyyou
Space for children, nice and good.
But 3-year-olds don’t need that much yet. The older they get, the more time they spend outside the house: send them outside into the garden or to the sports field. Later they hang out with friends, which can also happen at home on the bed or in front of the PC, but nearly 20 sqm isn’t necessary. Not even some living rooms have that. With 15 sqm, you can already call it “plenty” or “adequate.” Of course, next to a 1.40m bed you won’t have a 3-, 2-, or 1-seat sofa set, but at least a comfortable armchair. In this respect, the rooms can definitely be made a bit smaller. (Also, with a higher ceiling, you have more standing area.) Maybe not today or tomorrow, but soon. Tip: pencil and a quick fiddle make it faster! [emoji4]