Atypically high offer for ventilation system

What causes the floor construction on the ground floor to be 18 cm and only 13 cm on the upper floor? And if, it’s just a bit of Styrofoam. That costs nothing. More likely it’s the additional row of bricks to keep the room height consistent.

You don’t install a ventilation system to prevent mold. That is a nice side effect.

Today, I would not build a house without [Kontrollierte-Wohnraumlüftung]. I don’t consider that modern. I have retrofitted decentralized [Kontrollierte-Wohnraumlüftungen] myself, but that is not the optimal solution.

Why do you take them out??
We have a decentralized ventilation system with heat recovery, we measured 45-50% rh in each room individually and the windows hadn't been opened for weeks. In summer, you do summer ventilation and bring in the cool air at night.
Do you want and can you shock-ventilate 3, 4, 5 times a day in the first few years? Good luck.

So in 2021, the controlled residential ventilation with heat recovery cost us around €13,000 extra...

The controlled residential ventilation would cost us about 15k through the heating installer, we will now install it ourselves and have material costs of about 10k. The Blower Door Test is carried out anyway by the energy consultant and must be paid in both cases.

You don't install a ventilation system to prevent mold. That's a nice side effect.

Sort of. Eventually, even new build walls experience dew point undershoot. We've been inside since February and still have humidity levels routinely above 60%. And that's even though the fans are set to 4-5 air changes per day, and now in winter I also ventilate 1-2 times a day through windows. I don't even want to imagine how it would look without ventilation. Of course, comfort also plays a role. Ventilating in strong wind isn't fun, nor is cold air in winter. But I would never accept the builder saying there are no mold problems and therefore it's not needed. Unfortunately, there are still some builders who haven't made the leap into the 21st century. I would definitely try to build with controlled residential ventilation, and specifically a central one.