Building a retaining wall in the garden: formwork stones or L-stones?

Has the neighbor already implemented the excavation like that? How has it been secured so far? ... excavation is precisely regulated in the Building Code §909, who is responsible for what. We dealt with this because we are also on a slope and had to excavate on one side as well (although only 1m).

I am familiar with the paragraph, thanks anyway. Yes, he has, but nothing is secured there.

Pictures say more than a thousand words. In this case, however, the drawing is more expressive.

... since the forum currently does not allow editing...

Drainage: €37.00 per linear meter
Dimpled membrane: €10.70 per square meter

We will have approximately 20 linear meters, with an average height of about 1.5 m, so similar to you.

However, the situation regarding the neighboring property will certainly make everything more complicated and probably more expensive.

Which federal state? That seems quite expensive to me. Still, thanks for the information.

Yes, he did, nothing is secured there.

Well then...

Once again the questions:
And how will the drainage be done then?
By the way, please upload photos again. What does the terrain currently look like? How exactly is the neighbor planning? What have you (are you even talking to each other?) discussed together? How much space do you have?

Without information I say: If you want to build a wall now, a) several hundred square meters of land will not be properly usable because of a slope behind your wall and b) if you set a wall, a nice five-figure amount will be buried.
But the structural engineer will tell you that...

Which federal state? That seems quite expensive to me. Thanks anyway for the info.

Saxony. Whether it is expensive or cheap, I cannot say (yet), more offers are to come. Gardening and landscaping do not seem to have to complain about a lack of orders (at least around here)...

Images say more than a thousand words. In this case, however, the drawing is more expressive.

Whether drawn or photographed is secondary. But there must be an illustration, otherwise it remains a popcorn thread (and will lose subscribers hourly).

Yes, he did, nothing is secured there

o_O And don't you both have any concerns that your property could slip towards his? Have you ever thought about implementing the retaining wall together? Then you take 3m (+x due to installation depth) high L-angles and split the costs proportionally. You can't place L-angles, foundations, or walls on or at the demolition edge right now, as there is no support.