Front wall at toilet and washbasin

... the supply and return lines could then also be installed there in the screed.

... the supply and drain pipes could then also be laid there in the screed.

Yes, but they definitely have to go a bit into the wall, to the fitting and to the drain.

Why is that an advantage? (Seriously asking) As a blind fish, I don't find it very practical that currently (rental apartment) the mirror is "further away." But maybe I'm overlooking something (pun intended)

Good question. My wife likes it that way.

There are no pipes running in exterior walls.

This is only a recommendation in the relevant DIN. I just checked because in our house the sink in the utility room is also directly on the exterior wall.

It serves the "Convenience" planning and construction process. Planning, heat demand calculation, and construction produce the enclosed space more efficiently with less labor intensity when the shell core is constructed more simply and not made under partial re-machining. In the case of a "finished" house, it simplifies the installation, which in this case also streamlines the weather-sensitive part of the work. Regardless of the construction method, the rule "time is money" applies.

Oh, I really like the tiles... Do you still remember what they are called exactly? That would be great! :)

Thank you, that makes me especially happy since the tiles were also "properly" ;-) criticized here in the forum. They are from the company Steuler and are called Brush. When we bought them, they were available in yellow, blue, May green, and olive green. We chose May green. In the brochures, May green, May green Brush (with Brush, the colors run, similar to watercolor paintings), and white are often combined. I find that very beautiful and impressive in the photos, but for that, the bathrooms would presumably have to be significantly larger than ours. So we only chose "May green," without "Brush" and without "white."

We wanted colored tiles in the bathrooms because we need a little pick-me-up in the mornings. ;-)

Thank you, that makes me particularly happy, since the tiles were also "properly" ;-) criticized here in the forum

Oh, I must have overlooked that in your thread :D Since we are building a log cabin, I have been searching for nice touches of color that still have a harmonious effect. Many thanks for the manufacturer in any case, the tile definitely makes it into the shortlist!