Terraced house neighbor without a basement?

if we build a basement, that might mean a construction delay for him, he thinks.

I think so too. If you hire a really fast-working crew, they’ll have the basement up in four weeks. Your neighbor would have to wait at least that long to start his construction, unless you invest in an additional retaining wall, which would have to be built first in record time. Then your second question becomes moot:

Since it’s a terraced house, we would have to use his property for excavation, 3m, right?

With the retaining wall, you don’t have to use his property. It’s just significantly more expensive because some technical problems have to be solved additionally.

You can plan it well together. Then the neighbor just starts building 2 months after you, once your basement is finished. So what?

I think so too. If you hire a really fast-working crew, they will finish your basement in four weeks. Your neighbor would therefore have to wait at least that long before starting their construction, unless you invest in an additional retaining wall, which would have to be built first in record time. Then your second question becomes irrelevant:

With the retaining wall, you don't have to use his property. It's just significantly more expensive, because several technical problems would have to be solved additionally.

Thank you very much for the helpful answer!

You can plan that well together. Then the neighbor just starts building 2 months after you, once your basement is finished. So what?

Exactly, you can plan that well together. Provided he is willing to wait those two months. If he is not, then unfortunately we will probably be out of luck. Let's see what he says.

Exactly, you can plan it well together. Provided he is willing to wait these two months. If he is not, then unfortunately we are probably out of luck. Let's see what he says.

It's also in his interest. You could also say, you start 2 months earlier. :D

I am very grateful for answers to my questions, but I have the feeling you are using my question as an opportunity to make a statement of your opinion in general.

On the contrary, I consciously gave you suitable search terms for the forum search instead of repeating my words from there here in full text again.

And that is not very helpful and honestly also one-sided, because clearly such projects can also go wrong. But they can also go well.

I cannot see one-sidedness here at all, since I – as always – have pointed out that there are opposing views (and their proponents often also provide reasons, so that one can understand the views of both "factions"). And here opinions specifically differ on whether it is problematic in the end result or not.

But maybe I spoke too Chinese, so you overlooked the clarity of my answers? – I wrote, for example:

Surgically precise excavation with a slope angle of 90° only works in rock soil with the cutting disc, so "practically only in theory at all."

That says in German: Building ground – especially when another load is already pressing from above – does not stand firmly upright if you excavate next to it with zero distance "vertically (i.e. not at all) sloped." Rock would be solid (though at the expense of harder material to cut through), but normal earthy building ground is merely highly tenacious (but still too mobile to stand firm just by strict observation).

So, if you are "only" experienced in house construction and not also in mining, I see in that that the person building a basement adjoining someone without a basement builds first the central success factor.