Building height of 8.5 m with basement and 2 full floors

Can you explain that in more detail?

Just read the two sentences separated by paragraphs as what they are. Two separate paragraphs.

You were explicitly excluded from the statement "layman".

Two separate paragraphs.

That’s how I read it too: as a confirmation of Escrodas’s statement, and with an empty line afterwards indicating that lay speculation can shed little light.

Now there are different statements, also here in the thread.

You just have to read the plan correctly, both image and text. You don’t need to mind the awkward wording; the council members probably wanted to achieve clarity. Many builders today build without a basement, simply with a "slab-on-grade." Its upper edge is that of the concrete slab—otherwise, with an unfinished floor, some laypeople might wonder whether it means the screed upper edge beneath the tile adhesive. That houses with basements should then be one floor lower is certainly not the intention of the development plan. You will also encounter other terminological confusions, e.g., "wall height" being used to translate the eaves height on flat roof constructions, and similar things.

"For the Müller family we approve

You don’t need to worry about that; there is the principle of discretion binding = the same decision with the same facts.

I summarize:
You may build the upper floor regardless of "with or without basement."
Because of the different reference heights for eaves and building height (for pitched roofs: practically "ridge height") it can be a bit tricky to calculate the knee wall height and roof pitch optimally.
Your municipality is not the first and not the last whose development plans have to be read three times.
In Ecroda’s posts you already find good guidance, with professional experience and clearly separated what is knowledge and what is speculation.

You were explicitly excluded from the statement as a layperson.

Even so-called experts occasionally write nonsense, which is why I wanted to prevent misunderstandings with my inquiry.

Now there are different statements, also here in the thread.

Here in the thread, only you are assuming the basement slab. Who else shares your opinion?

Since I am still in the preliminary planning stage and accordingly have no planner yet,

If the planner has not already submitted applications in this development plan area, he will not be able to give you any binding information either.

I mean somewhere the municipality is also obliged to provide clarity

Yes, see §18 Land Use Ordinance. There should be a current justification for the development plan, in which every stipulation is explained again. Maybe there is a more understandable formulation here. If you have time and inclination, you can go to the town hall and read the current justification and, if necessary, ask an employee for an explanation. You don't have to identify yourself or indicate which property it concerns, even though I do not share your concerns about waking sleeping dogs. Not entirely serious but possible: If you have strong nerves, you can also simply submit the building application and, in case of rejection, question the legal validity of the development plan. It is said that development plans have been declared invalid by courts due to indefinite stipulations.

Even so-called experts occasionally write nonsense, which is why I wanted to prevent misunderstandings with my inquiry.

Of course, that only referred to your post in this thread. I don't know if you write nonsense elsewhere. :-p

So, enough off-topic now.

Hello everyone and first of all, thank you very much for your helpful answers. I have talked to the city planning department.

It is like this:

[*]8.5 m "building height" from the top edge of the basement floor slab.
[*]Buildings with a basement + 2 full floors are thus "forced" to have a flat roof.

Now my question: How do you evaluate this regulation of the municipality? Unfortunately, I lack experience in this and would of course comply with the rules

Also: Are the 8.5 m even sufficient, and are the floor heights/calculated dimensions realistic? Underfloor heating and proper insulation on the roof would be nice..

Basement: 2.60 m
Ground floor: 2.80 m
Upper floor: 2.80 m
Roof: 0.3 m <=== ???

And I have another question: For our building plot, the eaves height of 6 meters was specified. We leveled the plot privately. First of all, here is the excerpt from the development plan:

"The specified maximum eaves height refers to the height of the street surface adjacent to the building plot, measured at the street center of the plot center."

We measured these two points. The street surface at the plot center is about 1 meter higher. Do I understand correctly that my eaves may then be 7 meters above the ground? Or to put it differently, when I stand in front of my building, I see 2 full floors (~6 meters) standing on a basement that protrudes about 1 meter above the ground?!