Permitted building height (knee wall) according to the development plan?

A high knee wall (potentially also over 1.50 meters) is basically possible here in at least two ways (subject to other regulations in the development plan, which we do not know, and your personal preferences): 1) Excavating the terrain. Everything that is excavated is added to the 4.50 meters, since it is measured from the natural terrain (i.e. the figures contained in the site plan). The extent to which this is allowed would need to be checked (if I understand correctly, he suspects that such measures, if approved at all, would only be permitted to a limited or moderate extent). 2) The ground floor floor level could lie below the natural terrain on the uphill side, i.e. a ground floor slightly recessed into the slope on the uphill side.

There may be other possibilities. Therefore, it is definitely advisable not to consult only with a planner of a prefab house provider who is either rather clueless or not very motivated.

If you were to set the top edge of the floor slab at 0, the rainwater would be pressed into the house!

Presumably, it will end at least 30 cm above the level. 260 cm clear height, 15 cm floor construction and 30 cm ceiling of the upper floor result in a maximum of 85 cm knee wall. At 70 cm above ground level, you are accordingly at 45 cm.

I do not fully agree with these statements. The top edge of the ground floor floor can also be below 0 if it is designed correctly with regard to water. The basement is also below ground level on the uphill side.

1) Excavate the terrain. Everything that is excavated is added to the 4.50 meters, since calculations are made from the natural terrain (i.e., the numbers contained in the site plan). The extent to which this is permitted would need to be checked (if I understand @11ant correctly, he suspects that such permissions, if granted at all, would only be in a limited or moderate scope).

I actually meant more requests for terracing and especially embankments, to which I see little chance of success here. I do not see any building law objections to deeper excavation, ...

2) The ground floor floor could lie on the uphill side below the natural terrain, thus more or less a ground floor slightly recessed on the uphill side in the slope.

... however, I would like to question as a Pyrrhic victory the idea of designing the (in-the-)ground floor as the upper basement for the purpose of a (higher) knee wall. As proposed several times by (for weak slope situations), to recess the ground floor about a quarter meter, could be practical, but would not lead to great heights for a knee wall. Rainwater around the house must be drained regardless of the floor height.

Thank you very much for your answers so far. They have already helped me a lot.

Since the suggestion came up to dig out some terrain and build deeper: according to the plan, the sewer shaft is at 664.70. That means we should be at least at 665 with the basement slab to allow the wastewater to flow into the sewer, right?

Since there was some suggestion that we should dig out some terrain and build deeper: according to the plan, the sewer shaft is at 664.70. That means we should be at least at 665 with the basement slab to let the wastewater flow into the sewer, right?

I am not sure about the details, but I still want to praise that a questioner is considering this point. However, I would not want to push the house so far to the end of the property valley, especially since the road is located on the uphill side here.