What to consider regarding rear construction, narrow access paths, and co-ownership

Is there a fencing obligation on your property? And fences don't cost a fortune either. Include the cost of the fence and be happy if the neighbor contributes. You don't make a fuss over such small things before you have talked to each other.

So the risk is basically no longer on my side, right?

Yes. Now there is no target dimension anymore, but a verifiable actual dimension. When you buy, you become co-owner of an existing area as it is. So ask the land registry how it is.

And fences don’t cost the earth either.

No. Not the earth. But 100m of fence is also not negligible.

You don’t make a fuss over such small things

It’s not about making a fuss, but about gathering needs for regulation. There are supposedly chain-link fences that have gained great media fame due to the legal disputes arising from them.

I am still considering another direction: If the access path is exactly 3m wide, what happens if a neighbor demands a fence on the access path property? My research on the internet shows that (here in Bremen) there is no neighborhood law that prescribes anything, but does that mean no one can force me to build a fence?

but does that mean that no one can force me to build a fence?

Yes, unless something different is stated in the development plan or another statute.

It's not about making a big deal, but about collecting regulatory needs.

That is certainly true. What I meant is that you price the fence in as additional costs for the property and are happy with a good agreement. That takes pressure and annoyance away, because you have already prepared to pay it.