Is backflow protection really necessary?

Hello everyone!

We are currently in the process of building a house. On the upper and ground floors, there are toilets as well as non-faecal wastewater, in the basement only non-faecal wastewater from the washing machine.

The construction company has now equipped all inlets to the house connection with backflow preventers "Staufix DIN 50" in the plans, and the toilet on the ground floor additionally with a "Kessel Rückstauautomat Staufix FKA Komfort" for protection. This is now to be recalculated expensively, and the regular maintenance will probably also cost quite a bit.

Before we simply approve this, I wanted to familiarize myself a bit with the subject. After doing some research, I am of the opinion that not only the mentioned backflow preventer is unnecessary, but also all protections except the one for the basement.

However, I would like to be sure and hope for your advice.
Here are the key data:

The house is on a slight slope, here are the height details
Single-family house: 534.65m
UFH: 532.02m
HA KD: 533.88m (adjusted to terrain)
HA KS: 529.57m

That means, if I understand correctly, the backwater level can rise to a maximum of 533.88m, so still 0.77m below the raw floor level of the ground floor.

Who can tell me whether the protection is now necessary or not?
Thanks in advance :-)

If you are higher with EG than the inspection shaft, then please save yourself the lifting system for God's sake.

You don't need a basement either, a small lifting system and pressure loop over the ground floor are sufficient.

Thanks already for the answers, my assumption seems to be correct.

If your floor level is higher than the inspection shaft, then please for God's sake save yourself the trouble with a lifting system.

A lifting system was not planned by the construction company; the mentioned part is an electronic backwater flap (double) – it is normally open and closes electronically in case of backflow. There is also a control device attached, with self-diagnosis and all the bells and whistles. Using a sledgehammer to crack a nut, really.

That would be too much for me too, I'd rather go for a mechanical one. You can always use that imho, and it doesn't cost a fortune. Besides, I would invest in a closed piping system with an inspection piece in the shaft for wastewater. There are still cheap guys today who create open channels in the shaft even for blackwater.

That would be too much for me as well, better a mechanical one. In my opinion, you can always use that and it doesn't cost a fortune. In addition, I would invest in a closed piping system with an inspection piece in the shaft for wastewater. There are still cheap options today that create open channels in the shaft even for blackwater.

But the question is whether I even need protection for the ground floor toilet. Where there is nothing, nothing can break. I have to check the piping in the construction description or ask about it, thanks for the tip!