Semi-detached house in building area 8.5m x 15m (WxD)

How is the base height defined on a slope? In other contexts, the height is usually the average height of the slope. But that makes little sense for the base, because then the base at the upper end of the slope would disappear into the ground.

The reference is usually the street. You should know that, isn't it written somewhere in the development plan? Or ask?

What is allowed at SD 35-45°?

Everything that corresponds to that or is not excluded in the development plan.

Wait, I was talking about the floor area of the entire house

That is still wrong. has already roughly calculated it quite well.

140 m2 of living space per semi-detached house with 2 floors plus attic is quite a lot at today's prices. Especially on a slope. We are talking about 1,000k here.

How is the base height defined on a slope?

The reference height for the base foot is usually the average height of the boundary line between the building envelope and the access road, and not infrequently such a base is only granted to properties located upslope of the road.

Very interesting idea! What is allowed for SD 35-45°? Different roof pitches on both sides? Offset monopitch roof? Same pitch, but ridge not centered?

I was indeed thinking of "same pitch, but ridge not centered" (e.g. above the middle of the higher semi-detached house), but the combination with asymmetrical roof pitch would additionally be a permissible trick.

140 m2 living space per semi-detached house with 2 floors plus attic is quite a lot at today's prices. On a hillside especially. We're talking about 1,000k here.

I see it that way too. And thus no longer any contradiction between my ideas and the statements of .
For me, the living space is less decisive anyway than the room layout. My current home office measures 7m². And that is worth its weight in gold compared to the work corner in the living room in the last apartment a few years ago. And definitely more than 7 additional square meters in the living room. And yes: Everything I need for my work fits in there.

I think one could manage a floor plan reasonably well. Much more important are first of all all the boundary conditions of your property and whether the development with a semi-detached house can at all lead to a sensible use of the property.

Accesses, terrace locations (outside the building windows), etc.