Official liability building permit neighbor - keywords sought

The neighbor is hopefully smart enough to have the evidence secured beforehand.

Go multiple tracks. 1. Specialized legal advice 2. Written expression of your concerns to the building authority 3. Attend a building committee and ask citizen questions, even layman-like ones. The more people hear the concerns, the harder it is to "accidentally" ignore them. 4. Inquire about your options for securing evidence 5. Talk to the client of your neighboring house and also share your concerns in writing (initially without a lawyer).

Now you have already created a file situation that makes a later "I didn't know" statement unbelievable. Furthermore, there may also be a willingness to accommodate on the part of the building company - one does not have to assume opposition first.

Well, for you personally that may be something drastic, but the process happens all the time. If you were no longer allowed/could not build anywhere where a few old houses stand around it, everything would be full of building gaps. It will certainly be carried out in such a way that not everything around it collapses. That's standard. So if I were you, I would come to terms with the fact that you are getting new neighbors, everything else is unnecessary stress without any prospect of success. But a useful documentation of the current state is certainly not a mistake.

If you were no longer allowed/could no longer build anywhere where there are a few old houses around, everything would be full of building gaps.

The goal is not to prevent construction, but to protect the property or to get rid of the concern about it (it is unclear whether the property is even at risk). If that is given, will not have any particular problem with it either.

So if I were you, I would come to terms with the fact that you are getting new neighbors, everything else is unnecessary stress without any chance of success.

If the goal is no longer the protection of the property, you are right with "no chance of success." If the goal is to gain assurance that everything is done correctly, a clear commitment to that is very useful. Preventing construction is only one of several ways to protect the property – the most confrontational and hopeless one.

I am reading the description

my house is 200 years old and stands on a strip foundation. We live on an archaeological monument area near water with a groundwater level of 0.8m and on sandy soil.

already as a serious indication of a structurally sensitive house: 200 years ago, with high groundwater, they did not build a "white tank," but instead omitted the basement, and the keywords "strip foundation" and "archaeological monument area" also indicate that the house is not on a pile foundation. So figuratively speaking, the ground under the house probably has the "firmness" of an uncovered apple pie.

6m next to me, an investor is planning to build an underground garage for 3 apartment buildings.

The keyword "investor" also makes my suspicion not unfounded that they will keep no more than the necessary boundary distances. That driveways to underground garages are often laid in the building setback area is not uncommon. Typically, an investor relies on the building authority to impose the necessary conditions. Usually, they do not check the neighbors’ building files to see how their buildings are founded. Moreover, two world wars lie between the construction year of the OP’s house and today—so whether these building files are still even existent can be reasonably questioned. Without any indication of the quality of the foundation, the building authority would probably get away with, at worst, "slight negligence" or even have good chances of acquittal. Therefore, I do not consider the OP’s fears in the slightest to be hypochondria and find it essential to officially and with verified access to the special hazard situation due to the foundation to notify the building authority. As already described by in post #8, I would also urgently advise broadly spreading the notice of the particular dangers among the parties involved—though as suggested without resentful accusations of malice, but clearly with the indication that here not "just cracks" could be expected.

Is the investor known? Isn't there a contact person who can answer the question of how the neighboring buildings are protected and the construction pit is secured? There must be some architectural firm behind this. I hardly believe that it is such an anonymous investor aka [Heuschrecke].