Border height difference - Neighbor has built up twice

We have not moved in yet and have already had the first discussions with the neighbors.

It's about our difference in boundary elevation. At the moment, we are quite far apart. Our neighbor has built up the ground twice, on our side the topsoil was removed once and later quite a bit more was taken away, and a strip foundation for our prefabricated garage was placed at the boundary.

We brought up some time ago that something has to be done because of the height difference, especially since our neighbors have built up the ground and we will return to street level after the buildup and paving.

Today the issue came up again and we were told that they will go down half a meter and that we will have to bear the full cost for the supports because we have removed so much. €20,000 would be too much money for them (which I can understand). But actually, only the strip foundation was excavated on our side and later we want to have the garage at street level. Therefore, we are of the opinion that if something is done and they go down, the cost should be shared 50/50.
I also have to add that they claim they have not built up the ground and that we caused the difference by excavating. Therefore, they do not want to pay anything and apparently cannot afford to do so at the moment.

We suggested that maybe we could try it without L-bricks, if our garage can handle it. For this, however, the height difference must not be too high. We still need to ask how much. They would like to ensure that trucks can pass on their side for various works (garden planning and pool, etc.) and that they remain high enough so that their floor slab is not exposed (which is understandable). I believe they also want to park their motorhome there later.

Do you have any tips on the options we have here?

I think our general contractor can measure again with us and explain what height we will end up with.
I believe the state of Hesse says that if you stay close to the normal ground level, then both parties have to pay.

If necessary, everything except our garage and driveway must slowly be equalized, but here too I believe this must be done by both sides.

What I basically see as critical and still need to question is the slope that the property makes towards the back.
It’s best if I upload a plan.

I would really like a solution that both are happy with. But I am not willing to bear the full costs for it.
Well, maybe I am also misjudging the situation. Therefore, it would be good if someone is familiar with this topic.

I haven't looked at the plans yet (too tiny on the phone), but actually the natural terrain is the reference point. Our development plan states that a maximum of 50 cm may be added at the property boundaries in relation to the natural ground surface. If your neighbor thinks they need to add soil, they must also take responsibility for securing it, as they are also responsible for ensuring that rainwater stays on their property and does not flow onto yours – this should also apply equally to soil. In my opinion, therefore, your neighbor would be obliged to secure their property in relation to yours. If necessary, ask the district office/building authority/municipality or an expert about how the specific situation stands.

He just says he didn't pile it up. However, I have pictures where you can also see the change. But you can't see how much it was here. I think you always lose the overview there. For example, our GP can also measure the heights afterwards, right?

Whether he has filled in or not should be indicated in his submission plan, because there, just like with you, the natural terrain profile is marked. Alternatively, the contour lines also provide a rough reference point. Haven't the boundary stones also been surveyed? I can't tell you if your general contractor can do the surveying, he knows that better [emoji6] My opinion: if you are currently building on an undeveloped piece of land, it should correspond to the natural ground surface (before topsoil was removed). If his property was already higher, then he must have filled in. It's rather unlikely that such terrain is irregular and suddenly has jumps – especially right at the property boundary...

How was it again: You are the ones with the tree and the parking spaces, and the neighbor in question is the one next to you, opposite the bend in the street?

At least I see contour lines on the plan, which refer to the existing terrain in the road planning or development plan preparation. You can compare them with the current state and see whether the textual provisions mean that they are within tolerance.

As far as I have read here in various threads about elevation issues, it is apparently common in all federal states that the terrain modifier is not allowed to extend their desired height all the way to the boundary, but – and mind you, so that no drainage goes onto the neighbor’s property – has to slope it off so that it practically returns to the former height at the boundary.

L-bricks must be on the side of the higher property owner, otherwise they are of little use. Without L-bricks, would their embankment then press against your garage wall, or how am I supposed to imagine that?

The question is, who changed the terrain by how much, where, and when? According to your plan section, the terrain once sloped quite uniformly with about 6% gradient. Your finished floor level on the ground floor is at 176.15, your garage at 176.45, and the neighbor’s finished floor presumably 80cm higher. In the area of your garage, the planned terrain is drawn identical to the existing one. I don’t understand where and how much you have excavated and why. If this was only for the construction measure and you later fill back up to the natural terrain level, then no disturbance originates from you. And what does the terrain currently look like? How many centimeters has the neighbor added how far, and what does the transition to your property look like? So the slope is not steep enough now to require elaborate slope stabilization. The incline to the back is also only half a meter over the entire length of the property. Has a specialist ever looked at it? Maybe you are seeing problems here where there are none.