Load-bearing capacity of L-stone and water drainage at 45° slope

I will definitely do that, I just assumed that a company must also stand behind what they build and backfill, especially a several-ton heavy wall with backfill that has to hold a lot.

From how many degrees does the slope stop being problematic? Or let's say at what degree of inclination do you no longer have problems with the plants?

Can you provide information on how far I have to set back from the property boundary to be allowed to build further upwards (in BW)? Possibly a second row made of stones, for example, would make sense at the critical point.

Only the landscape gardener can really answer that for you. Too many factors come into play. Soil quality, climate zone, substructure, drainage, etc. In some regions, for example, a "rock slope" would be conceivable instead of a embankment, but that quickly becomes expensive.

I never would have thought that plants would pose such a problem, let alone that there would be maintenance involved. What kind of plants are those on the flat roofs? They are rather very flat and wide (so little surface area), only get rainwater, grill in the sun all day, and receive no love at all…

If you plant something, there is maintenance involved. You also have to go up on the roofs every 1-2 years and check that no small trees are growing. I also don’t know of any roof on which something actually grows that is attractive; they all seem to be botched. Otherwise, with such a steep slope above a ledge, the topic of planting is already problematic; I assume the BG will not allow unsecured work there. For the plants, you should look for something that really requires no maintenance. No weeding, no mowing grass, no pruning of trees or shrubs. Also, on a slope without terracing, rainwater mainly runs off on the surface, so you need species that can cope with drought. Furthermore, no leaf drop, since you certainly won’t want to rake leaves up there. Another point that comes to mind spontaneously is the snow. At 45 degrees, something will surely slide off more often, especially when snow falls from the branches. What is planned below the wall/slope? I would definitely prefer terracing if it is financially feasible; possibly you could also gain usable land that way, e.g., for a kitchen garden?

From my point of view, a structural engineer is needed here first, who can make a reliable statement based on a soil survey.

How is the house supposed to be founded now?
There is only 3.5m distance to the house wall.
If the soil structure or its support is not stable (storms, erosion over decades), there can be a soil failure or a landslide.

The slope does not end at the top edge of the L stones, but continues there undiminished with 100% gradient.
A landslide can also occur in this upper area (on which your house partially rests).

If you want something artificial like this and don’t have the time to let the soil secure itself with trees and shrubs, more will probably be needed than a "small" retaining wall made of L stones.

I am thinking of earth anchors with shotcrete or metal mesh.

Planting should be considered in the second step. First of all, the slope must remain stable.

The issue of drainage will also be very crucial. Where could a ditch (for the hillside water) and the drainage be connected underground?

The water has to go somewhere. Is there a sewer connection or would the lower neighbor allow it to be discharged through their property?

Or does the development plan require the precipitation to infiltrate on your property?

All of this must be included in an overall concept. Because even if the 2m wall in BW is exempt from approval, you as the owner are responsible. If something does happen, the natural hazard insurance will certainly want some proof of stability.

Please excuse the negative perspective.

I do not see L-shaped stones here as the appropriate solution either. I would also resort to solid and reinforced concrete walls. The water must remain on your property. Build a large cistern behind the wall. Install a gutter at the edge of the wall and direct the water into the cistern. You definitely need to seal the wall, otherwise water will penetrate through. Talk to the neighbor to find out what his problem is. Is it really the structural stability or does he just not want a wall.... Maybe he can also give you valuable tips or even help.