Increase knee wall height - exceed eaves height?

The full floors refer to the front property. We want to build behind it, and the suspicious hinterland regulations apply there :-(

How does it work with burying the base plate in terms of moisture from rain or similar? Is that a common procedure?

I would always keep one step into the house, precisely to make it harder for water. Kaho, aren't you forgetting now that with underfloor heating you also have to account for about 15 cm for insulation, screed, and flooring? For my part, only 20 cm for the concrete slab itself, but that in the ground floor and upper floor, and it already becomes tight.

...We are currently in the more detailed planning phase for our construction project and are currently obtaining offers from potential construction companies. We have currently received a plan that basically suits us. However, the problem here is the knee wall in the upper floor of 75 cm after conversion with a roof pitch of 42°...

Since no one has commented on the roof types: Search for "mansard roof" There might be something possible, although rather in collaboration with architects than general contractors, construction managers, etc. etc.

Since no one has commented on the roof shapes: Search for "Mansard roof"

Yes, I did in post #17, and the building authority had suggested it (see post #16 by the OP).

Problem knee wall