But install a controlled residential ventilation system?

Oh, I understood it now as meaning that these are now in the raw floor [Rohfussboden].

Is that a wise decision? I'm thinking that we should definitely lead water away from the house, because we want to avoid bringing it in

take out a good natural hazard insurance (not to scare you) - unless your property is situated higher anyway.

The single-family house is set at 402.5 according to the plan, but the street in front of the house slopes slightly from 402.39 to 402.26. The finished floor level is therefore at 402.45 and there will still be a small step in front of the house. I know this problem from acquaintances who also live on a slope and had a stream running through their house after a dry summer when there was a heavy rainstorm. But according to the architect, the water should be able to flow off sideways without any problems and there is an additional drain in front of the main entrance.

Axo, I had understood that these are now in the raw floor

Our ground floor ceiling is only 18cm thick as well, which I also find problematic, so I would like to integrate these into the floor construction. But I would have to clarify that with our basement builder.

With an 18 cm concrete ceiling, that is already possible - which I have now done as well. However, you then have to bend the reinforcement a bit, otherwise the pipes won't fit through. But it was only a small piece with the crowbar...

With an 18 cm concrete ceiling, that is already possible – I've done it myself now. However, you have to bend the reinforcement a bit, otherwise the pipes won't fit through. But it was only a small bit with the crowbar...

I hope your structural engineer approved it that way...

Yes, of course - why do you ask?

Picking up the actual topic once again...

Whether a controlled residential ventilation system is to be installed or desired must always be determined or calculated by the planner, architect, structural engineer, or other specialist planners. The minimum requirement that must be ensured with a ventilation system is the so-called moisture protection (FN). The system must at least be designed for this. For comfort, the system should then meet the required nominal ventilation (NF). NF is the amount of air necessary to achieve a complete air exchange within a certain time without window ventilation.
At least that is how I plan my systems.