That would be a Schildbürger (master) prank of the highest quality and a perfect setup to overturn the development plan.
But I rather believe an apprentice was on the phone. Development plans are meant to standardize the appearance of an area, not to create a restless skyline by capping the height of basement houses.
In my opinion, the office has 3-4 employees. On the phone, I spoke to a colleague of the lady who created the development plan (she was on sick leave). He was familiar with the situation, as builders before me who have built in the area had this problem.
His summarized statement in roughly quoted wording: "We are aware of the problem. Unfortunately, we can only offer you the option to go through an exemption application. However, it would have a good chance of being approved. Just make sure you don’t exceed 8.5 m too much." When I asked what "too much" means, he said up to 9 would still be okay. Our dream house plans a value between 10 and 11.
What do the textual regulations say about the height references to unchanged terrain and the boundaries of such terrain modeling?
I found nothing on that. As before Escroda, I will send you the plan once via PM.
The question for you now is whether you want to pursue legal action if your dream house building application is rejected. Are there no houses yet in the building area? Do you know other builders there? Have you already spoken with an architect?
The building area is about 75% built up to this day. I don’t know any builders and unfortunately live 300 km away. But I know from the city planning office itself that especially builders "in the hollow," meaning all building plots downslope (northeast), had to deal with this problem. Our neighbor has now built a huge house without a basement (hardly any garden left). Across the street, there is a small house with a basement (in my opinion, too small). Both have families. I would NEVER have built like that!! Whether that is related—quite possible?!
We are currently researching architects. I have been in contact with one since today.
(I then come to point 258.81). From there you take the shortest path to the middle of the street (I then come to point 258.81). The eaves of your house may be no higher than 6 m above this point (thus a maximum of 264.81 above NHN), completely independent of the terrain heights on your property.
So just to make sure I understood correctly: the eaves may NEVER be above 264.81 above NHN? Since the terrain slopes down about 1 meter from the planned house footprint, this would mean that my basement may protrude up to 1 meter out of the ground on the downhill side. But the uphill side of the building must be underground. And since the basement cannot count as a full story, about 3/4 of the basement would be underground, and from the last quarter there would be a slope exposing the basement up to 1 meter (where the office and guest room are located, with normal windows facing the garden).