Is controlled residential ventilation necessary with expanded clay and KFW55?

Simply leave out the ventilation. Decentralized is absolutely unsatisfactory. Save your money on such a lousy solution. Also skip the window rebate things.

Centralized or nothing at all.

Decentralized is absolutely unsatisfactory.

Please tell the OP why.

Also leave out the window rebate things.

I agree with that too.

I would not build without ventilation nowadays. But it is an old discussion... I just installed decentralized ventilation in existing buildings at great expense. CO2 levels in the bedroom and humidity in the bathroom were simply too high ... But there are also people who leave bedroom doors open at night for children and cats ...

But there are supposed to be people who leave bedroom doors open at night

Of course the bedroom door stays open. What reason (other than the children should not find out what the parents are up to ;) or pets should stay outside) is there to close the door in the bedroom?

I could now respond with a factual reason (closed door is safer in case of fire), but honestly I just want to be left alone ;-)

Tell the OP why, please.

I agree with that too.

It's enough if he does some research. He can find a lot about it here as well. There is a reason why most people turn those things off. They are too expensive for that.