Who has to support the property?

Hello!

As soon as my property is purchased (notary contract already signed), I wanted to talk to my future neighbor because my property will soon need to be filled. I have drawn a small sketch of the property layout in Paint; I hope the drawing is understandable.

About the colors:
Black = course of the street/side street
Red = course of the neighbor's property
Brown = clarification of the slope on the neighbor's property
Orange = already built retaining wall of the neighbor (he uses the area in front of it as a parking space for his car)
Pink = my neighbor's house as well as a small "bridge" to his front door (the lower "box" here is the basement/lower ground floor, the upper box is the ground floor; above that is the upper floor and the attic).

As can be seen in the profile section, my neighbor's property has a steep slope at the property boundary to my property (red course). I want to fill my property to the level of the side street (building with a basement and a terrace on the north side, but for this I will build a retaining wall myself, the neighbor has nothing to do with it). So my property will be as high as the adjacent streets.

Who has to pay for the costs of the retaining wall? Do I have to pay because my neighbor has already built his house? Or does he have to pay the costs because he wants his property to be so low (he uses the area in the south as a terrace for his basement floor; the area in the north is his garden - but it still needs to be filled further because his door to the garden is currently "floating," meaning the garden is not high enough). I think he is waiting to fill his garden because otherwise all the soil would slide onto my property.

Thank you very much for reading and (hopefully) constructive contributions!

Regards

Since I can no longer edit my post: There is no development plan here because most buildings are older. Only my neighbor's plot and mine were recently sold. My neighbor's building is (I assume) at most 2-3 years old. All other buildings in the area are at street level; only my neighbor's and my plots have/had to be filled. The plot is located in NRW.

I completely agree

I have the same case with my neighbor at my property boundary. We have discussed it extensively, but he has never come up with the idea that I should contribute to his retaining wall. I would also find that quite absurd. What rather puzzles me is why the building authority approves such oddities.

Best regards

K1300S

The building authority seems to really approve everything at this location; the whole street is a colorful mix of houses with different facades, ridge heights, roof pitches, roof shapes, etc.

Then I need to talk to the neighbor about sharing the costs; we would both benefit from it. I could build my garage on the south side and he could mound up his garden. If an agreement is reached and you want to put it in writing that you are jointly building a wall, is it enough to sign a self-written text (e.g., We, the owners of parcels XY and YZ, agree, etc. etc.) or do you also have to go to a notary for something like that? I have never had such a case before and therefore do not want to do anything wrong.

Thanks for your contributions!

I think you can handle it like this for now - but also keep in mind that such a wall also needs to be maintained (costs) and possibly the neighbor might move out (legal succession).

Regards

K1300S