Is backflow protection really necessary?

A mechanical flap costs 50-100€. That won’t be the problem. Despite all (physical) laws, I wouldn’t do without it. Rats also get caught on it. But yes, it’s a matter of mindset and where there is nothing, nothing can break, get blocked, or anything else.

Hello

Not necessary for EG and Og
For the basement, a small lifting system with a drain above the backflow level.

Olli

Hello! Thanks for the many answers.

In the meantime, I have understood where the problem lies. After further research, I suspected that the construction company took the next higher shaft from the neighbor as a reference point instead of the connected one. I then reviewed my documents again and indeed found a sectional drawing on which the backwater level was marked - at half the height of the ground floor, and roughly (not marked in my plans) at the height of the neighbor’s KD.

This means that the subsequent planned safety measures are correct if you assume this RSE.

However, in my opinion, that cannot be right, because according to the plans I have, I am connected directly to my shaft, and only there should there be a connection to the next higher shaft via the sewer. Accordingly, there can be no possible blockage in between, because there should be no "in-between."

I now have to contact the construction company; they have to explain this to me precisely. I will then report on what came of it.

Oh, now I understand. The shaft I am referring to is an inspection shaft, not a street shaft. The next street shaft is probably up there. Of course, that is not included in the plans. So it fits.