Are the construction costs listed correctly?

The ventilation now doesn’t cost that much either: 15,000 for the central unit and just under half for the decentralized one...

why is there only 2.30m room height on the upper floor? Why are you installing radiators upstairs?

Regards
Sabine

So I'll leave it at that. The costs are already enormous, especially in service phases 5-8.
Ventilation is not going in. Neither my wife nor the architect nor I are fans of it. Such ventilation systems also do not have the best reputation. But everyone has to decide that for themselves.

There is a reason why it costs so much. You don't just do that on the side.

You can't do the execution planning yourself anyway (that's service phase 5).

Where you could do something like that is if you already have someone from the field (i.e. service phases 6-8), and a lot of time.

2.30m result from the development plan. (Max. height of the house). I need to see what can be done by myself and what rather cannot!

Have you ever "visualized" 2.30?

Because that is almost a full 30cm less than what I know as room height.

Honestly, I can't imagine that something like that is enforced by the development plan. I would check again carefully. 2.50 is actually a minimum size.