Slightly below the finished road, backflow prevention?

Hello,

the planner of our house does not consider a backwater valve or something similar necessary or has not included such a thing in the drainage planning. It was said something like if the planning "goes through" like this, we wouldn't need one.

We are total laymen and want to hear several opinions again.

The upper edge of the finished floor will be 5 cm above the "height reference point" on the drawing in the attachment (drainage planning drawing). However, the fully developed street will be somewhere between 5 and 15 cm higher than the construction road.

We have a toilet and a shower on the ground floor.

Thank you in advance...

Hello

All processes located below the backflow level must be drained via a lifting system.
That means, for example, if a walk-in shower is located below the street drain cover, a lifting system is necessary. A backflow valve is not sufficient in this case.

Olli

We will now have it checked again to see if the house can still be built a bit higher. The building notice has already been submitted (and is basically approved). Let's see if there are any problems...