Sealing retaining wall neighborhood

Hello everyone,
my neighbor has excavated about 1.2m. Therefore, he built a retaining wall (about 25m long) with formwork stones along our boundary.
I have my terrace (uphill) and need to fill the soil directly up to the retaining wall.
My neighbor even excavated soil from my property (about 1m wide).

Question:
Who is responsible for the sealing, e.g. with dimpled membrane, and who has to pay for it?

Thanks for your answer.

Why seal? Should the neighbor take care of it if he wants a seal. Did he have permission to dig on your property? We also built a retaining wall to the neighbor. We get along great. We take care of everything.

Why seal? The neighbor should take care of it if he wants sealing. Did he have permission to dig on your property? We also built a retaining wall for the neighbor. We get along great. We take care of everything.

Permission: of course NO. He said it was better for me. In reality, it is even bad for me because I have no working space. But for me, these are minor issues.

At the very beginning, I was active in communicating with him. He was the opposite. He first built his wall on my property (15m2). Meanwhile, after 4 months (without escalation, luckily) he dismantled it and built a new wall.
After demolition, he once tried to pass the costs of the new wall to me. I refused because I did not alter the natural terrain.
Now he would like me to do the dimpled membrane for him.
The costs of about 500-700€ for a house are not huge. What annoys me is that he told me it is my responsibility.
I once read that rainwater must infiltrate on your own property. Now I am afraid that if rainwater runs over the soil onto his wall without the dimpled membrane, for example after 10 years it will damage his wall. And then he will sue me.

Permission: definitely NO. He said that it is better for me. In reality, it is even bad for me because I don’t have a workspace. But these are minor things for me.

At the very beginning, I was active in communicating with him. He was the opposite. He first built his wall on my property (15m2). Meanwhile, after 4 months (fortunately without escalation), he took it down and erected a new wall. After demolition, he once tried to pass the costs of the new wall onto me. I refused because I did not alter the natural terrain. Now he wanted me to do the dimpled membrane for him. The costs of about 500-700€ for a house are not huge. What annoys me is that he told me it is my responsibility. I read once that rainwater must seep into your own property. Now I’m afraid that if rainwater runs over the ground onto his wall without the dimpled membrane and damages his wall after, for example, 10 years, he will sue me.

you don’t have to. his wall, his membrane.

Hello everyone, my neighbor has excavated about 1.2m. Therefore, he built a retaining wall (about 25m long) with formwork stones along our boundary. I have my terrace (at the top - hillside location) and have to fill the earth directly up to the retaining wall. My neighbor even excavated soil from my property (about 1m wide). Question: Who has to take care of waterproofing, e.g. with dimpled membrane, and pay for it? Thank you for your answer.

If you have not changed the slope at the boundary, you do not have to do or pay anything except contribute to the boundary fence. We also have a slope and your specific situation is very pronounced with my right neighbor as well. That means he himself at the top has not changed his slope and at the bottom, excavation was done to 1.5m. Result: The lower neighbor had to bear the measures to retain the terrain completely on his own. And now it gets even better, since the neighbor’s architect (also planner of our building area) researched it. The lower neighbor must also tolerate the upper rainwater. In other words, he must tolerate puddles forming at his boundary wall from above, but naturally not mudslides from above.

He does not have to participate in anything in BW. In other federal states, it is partially regulated differently. It is the neighbor's matter and completely so.