Neighbor is building a retaining wall on my property. What should I do?

Since no formal approval is required

Why not? The wall itself is exempt from procedures, that is correct. However, it contradicts the provisions of the development plan. Therefore, at least a separate application for exemption from the provisions of the development plan is required. § 56 para. 6 State Building Code. But here construction is taking place in connection with a project requiring approval. That is why he needs a new building permit for everything.

But here, construction is taking place in connection with a project requiring approval.

We know too little about the exact circumstances and procedures that applied to the neighbor.

I consider it unlikely that the authority will intervene in the neighborhood dispute.

Aside from that: If I had a permit for a 1.20 m wall and then "tried" 1.50 m, if this were discovered, I would probably cut off the top 30 cm rather than demolish the entire wall and rebuild it. Conclusion: The wall is still on the wrong property, but the building authority will definitely no longer bother.

Therefore: Make clear statements and do not try to achieve an uncertain result through a long causal chain behind the scenes. The neighbor simply has to be put in his place, and that only works if he understands that the dismantling must be complete and not just a correction of an excessive height.

Can someone quickly tell me which federal state we are in?? Because of the state building code??

Administrative law is also largely a matter for the federal states. But apart from the fact that the Building Code (use of the neighboring property) is federal law, the states should basically agree not to let authorities be used for civil law clarifications. I see aspects of the state building code in this thread at most as "tangentially" touched.

I also see a problem in that the wall belongs to the person on whose property it stands. No matter who built it. Just because of that, I wouldn't be interested. If something happens with the [Beast], I also have to repair it.

I see land building regulation aspects in this thread at most as "tangential".

I only asked because in BaWü, in individual cases, even pure formal illegality is enough for an order from the building authority. This is not the case in other federal states. Of course, this is only a crutch. Because mainly private law is involved. We all agree on that. However, I try to point out the "cheapest" possibility. The neighbor will not respond to a self-written letter/email and what an hour at the lawyer costs....... It is better, even if only with crutches, to send the building authority out for free.