Unplanned retaining wall

You can also build a wall from formwork stones or planting stones. That is cheaper than a classic wall.

But with that height, it is strongly advised against. Otherwise, you'll have to deal with it again after 10 years because they bend away.
You won't get around using wall panels/ L-stones.

Do I understand correctly that you are building with a slab foundation on a slope? If something goes wrong with the new wall, will your house not be stable again? Would it be an alternative to build with a basement? But it is probably too late for the change?

Do I understand correctly that you are building with a slab foundation on a slope? If something goes wrong with the new wall, will your house not be stable again? Would it be an alternative to build with a basement? But it is probably too late for a change?

Yes, slab foundation on a slope. I have drawn it with all my skill (see attachment).

1) Sidewalk
2) Street
3) House
4) Wall

There are about 3m between the house and the wall. The drawing is of course not to scale. The steps behind the wall are wider and also not all that high. And I don’t think there are that many.

The L-beams are supposed to have an L-beam dimension (do I understand correctly that this is not the height, but the footing is included?) of 2.8-3.1m.

I will mention the basement, but I suspect it is too late for that (everything already planned and approved) and it would probably be more expensive than 22k€, right? Of course, you would then have to subtract the money for the thermal slab foundation partially, but I still think the basement would be more expensive, right?

Clearly, a basement is even more expensive. But then you also have a basement. What about the walls of the other levels? That is quite an extraordinary location.

I just looked at some pictures, the next steps are together maybe about one meter high. I estimate a maximum of 2m slope over roughly 20m. So around 10%

Ok, that’s then clear. But your sketching skills can still be improved just a little bit ;-)