KFW 50EE or 40EE - Is the upgrade worthwhile?

It is certainly more sustainable and economically efficient than the EE at 40

The EE is mandated due to the connection obligation to local heating (biogas).

Only the question whether 55 or 40, not....

Regardless of KFW40 or 55, I would not want to build without a central controlled residential ventilation system.

Now talking to the two most well-known in the area. Possibly also with a third one with whom the colleague is currently building - however, I do not like that the manufacturer of the ventilation was changed during construction without consultation...

"Or comparable" is an option that can be taken at any time. The reasons for this are diverse and not per se untrustworthy.

Just want it to be solid

Why "solid"? - especially the wish for KfW40 is regularly fulfilled much easier and more routinely by the timber frame panel builders (see my Steinemantra). As soon as you have found my post, you also know the way to contact me.

Do not want a wooden house... Changes during construction no longer possible... Special requests beyond the normal house are very expensive

Special requests beyond the standard house are super expensive

What would those be?

Changes during construction are no longer possible

Geez, then you just have to tighten your belt a bit and think about the sockets a little earlier and more thoroughly or just equip them on the right and left of the TV ...

Which ones would those be?

Jeez, then you just have to pull yourself together a bit and think about the power outlets a little earlier and more thoroughly, or simply equip them on the right and left of the TV...

You can’t easily convince someone who wants to build massively. My first house build was also with bricks and nobody could imagine it otherwise. Second project then timber frame construction and my father (formerly a mason, but already away from construction for 20 years at that time) first smiled at me, then he was impressed "how things are done these days" :-)