How much setback from the boundary for a house on a slope? (BW)

Your balcony extends 1.6 m beyond the building area. In my opinion, the exception rule only applies to terraces.

Unfortunately, we did not have the decision. South of our property, there is still a rather large steep slope plot that can only be accessed from above. That is probably why the city demanded this part in order to possibly build a small path/road to the property later. For this reason, there is also this small corner at the bottom.

You mean something like this? Would the drainage points be roughly as marked (in red)?

No, I meant either a diagonally sloping shed roof or a multidimensionally ("gable" of different heights) pitched gable roof to align the roof pitch with the terrain (albeit more gently slanted in comparison). Simply because it mitigates the height restriction issue. Side effect: extravagance for little effort. Red = low points / drainage, +/++/+++ = relatively higher points. +++ is about 1.2m higher than the drainage, but the parapet runs parallel: (top = street)

No, I meant either a diagonally rising shed roof or a multidimensionally ("gable" at different heights) pitched gable roof to align the roof pitch with the terrain (even if more gently slanted in comparison). Simply because it eases the height restriction issue. Side effect: extravagance for little effort. Red = low points / drainage, +/++/+++ = relatively higher points. +++ is about 1.2m higher than the drainage, but the parapet runs parallel: (top = street)

I actually had a phone call earlier with a carpentry company and they also had a very flat gable roof as suggested in your drawing and then covered the roof with sandwich panels. This would have the advantage that it would add the least height and if it were built without a parapet (if possible and not too ugly visually), you would of course also gain some space regarding the setback distance. Regarding the balcony, I would inquire at the city. If it is a subordinate part, it would probably protrude 1.5m beyond the building envelope.

Actually, I had a phone call earlier with a carpentry company and they also had a very shallow gable roof as suggested in your drawing and then covered the roof with sandwich panels. The advantage of this would be that it would have the least protrusion, and if it were executed without an attic parapet (if possible and not too ugly visually), one would of course also gain a bit on the boundary distance.

By referring to it as a "gable roof," I did not mean to imply a traditional carpenter's roof, but merely to suggest executing the flat roof with a kind of central ridge. I am thinking of a green roof without an overhang. The roof pitch here does not need to fully exploit the 5°, and a three-dimensional slope also allows sufficient drainage speeds even at a shallower pitch. The greenery additionally has a relaxing effect on drainage. One should not imagine an attic parapet as a standing collar / trough; it is actually just about an edge that does not need to enclose more than the structure of the roof covering.

By calling it a "gable roof," I did not intend to imply a carpenter's roof, but merely to suggest executing the flat roof with a kind of central ridge. I am thinking of a green roof without overhang. The roof pitch does not have to fully utilize the 5° here, and a three-dimensional slope also allows sufficient drainage speeds even with a shallower pitch. The vegetation additionally has a relaxing effect on the drainage. You don't have to imagine the parapet as a standing collar / tray; it is really only about an edge that does not need to enclose more than the roofing structure.

Ah, thanks for your explanation. Maybe the carpenter meant the same. And he wouldn’t be responsible just for the roof, but for the whole house with solid wood walls (if financially feasible). And in that case, would you make the parapet, say, 10cm high and let it run down along the slope? How would you handle the gable ends? Extend the parapet up to the highest point? Does one have to drain a flat roof "internally," meaning on the roof surface itself, or could one also work with a gutter here?