Floor plan design for a two-family house on a slope

I used the wrong term there. It is not a skylight. It should be a fixed window that starts at about 2.2m room height and goes up to just below the ceiling (2.7m).

I used the wrong term there. It is not a transom window. It is supposed to be a fixed window that starts at about 2.2m room height and goes up to just below the ceiling (2.7m).

That is also called a transom window [emoji2]
A transom window/light strip is not necessarily intended for exterior walls.

even if we didn't accept everything.

you said that nicely

One can only hope that the matter is somewhat mitigated by the shift backward.

Yes and no. Basically yes - but: as soon as you look at it at a steep enough angle to perceive the depth offset, you also see the interplay with one of the diametrically colorfully mixed sides :-(

Roughly speaking, then 42 degrees on 13m is just under 12m of slope. Is that correct??

Ninety percent or eleven meters seventy. Let's hope that 42° is meant, that would be just under 23% or three meters ...

Ninety percent or eleven meters seventy. Let's hope 42° is meant, that would be just under 23% or three meters ...

Huh? I might be mistaken, but if I tilt something 45° from the horizontal towards the vertical, the resulting plane rises/falls exactly 1m for every 1m of horizontal gain. That makes 100% to me. 42° are therefore over 90%, and I certainly hope the property doesn't look like that?

A 23% slope would be about 10.5°. At least with 3m, I can come up with that.

Where is my mistake in thinking?

I used the wrong term there. It's not a transom window. It should be a fixed window starting at about 2.2m room height and going up to just below the ceiling (2.7m).

No, my mistake. I would simply extend this transom window all the way down. That gives the shower much more light and also adds interest. Especially when guests come over.

Where is my flaw in reasoning?

Not yours, mine
oh crap ... the phone rang while I was typing on the calculator. Multitasking mess.

Let's hope that 42° is meant, that would be just under 23% or three meters ...

should have said:
Let's hope that 42% is meant, that would be just under 23° or five and a half meters.