Retaining walls at property boundaries. Who is allowed what?

3 m height difference: off to the (structural) engineer. No ordinary shuttering blocks can handle that. Find a joint solution with the neighbor. This way your wall will later receive additional load from the angle supports.

The neighbor has an easy time, your wall falls down

Please do not take the proportions in the graphic seriously. It is only meant for clarification.

Well, I wouldn't want to stand next to the wall there. Your wall receives the lateral force from the foundation of the L-blocks. Even without the L-blocks, there is already a massive earth pressure acting on the formwork blocks.

For me, it is still questionable whether such a structure is even allowed to be built.

In unserem Bauantrag

So you applied for the simplified procedure according to §66?

Sieht man schön in der Profilansicht.

I see nothing, no site plan, no elevation, no development plan. If you withhold information from us, you cannot expect any help.

Dort ist auch der Höhenunterschied, Grundstück Anfang bis Ende angegeben.

Also how this height difference is to be overcome (wall, embankment, ...)?

Wird bei der Baugenehmigung auf sowas geachtet, also ob es zu solchen kostenlationen kommen kann?

I hope so, but the procedures in RP and NRW differ considerably. Maybe you should ask your designer about this.

Ich meine, der eine weiß ja nicht was der andere vor hat.

That’s sad. Neighbors have to coordinate if they make changes near the boundary. If they don’t, they have to fix the mess at the end. Since everyone feels justified, they waste urgently needed money on lawyers.

The template in the picture looks somewhat adventurous. Property boundaries are often very emotionally charged. If you can agree that your boundary has a certain width, e.g., 2m (1m from each property), on which a significant height difference is secured, you can approach and finance the entire construction as a joint project. A slight embankment against the slope helps to make the whole thing more feasible in terms of price-stability ratio. For the conversation, I would set exactly this goal in your place: to reach an agreement on finding a joint homogeneous solution taking into account the overall static structure of the slope location.

exactly like that... regardless of statics and costs: you simply can't build a 25m long and 3m high wall on the property boundary. What does that look like, what is it supposed to be? A commander's hill on top and a prison down below :-(