KfW 55 - Ventilation system yes/no? - Experiences

What would still be interesting, if I build KfW 70, is a ventilation system then totally pointless? Would that really be a disadvantage? Just for my understanding. Is that even done nowadays?

You can find the answers to that in my post!

It makes no difference whether you build 70 or 55 or 40, the houses are airtight!
That means either a ventilation system or corresponding manual ventilation.

I would even argue that with 70 or the Energy Saving Ordinance you have a faster mold problem because the exterior wall is correspondingly thinner and thus the temperature on the inside might be lower and water condenses more easily than with the better insulated KFW55 wall.

You also have to realize that the KFW “standards” are just clever calculations. Depending on how you build, for example, just to comply with the energy saving ordinance, it may well be that when you recalculate, you find: oh, that’s even enough for 55.
A bit of insulation on the floor slab here, a bit on the roof there, decent windows and suddenly you may realize that you have achieved KFW 55 without it being intentional.
KFW is just clever calculating.

For KFW 55, you certainly don’t need a particularly insulated wall.

- 10k surcharge for thermal insulation measures

I would find it quite interesting to learn what kind of "thermal insulation measures" those are. Hopefully, no one comes up with the idea to simply stick insulation boards onto the bricks. There are definitely much better ways to do that, as Tarnari rightly pointed out:

For KFW 55, a particularly insulated wall is certainly not necessary.

One should really only build energetically if they have the money or out of conviction. It usually doesn't pay off. I say this as someone who naively wanted to build a real [Passivhaus] at the beginning.

Didn’t find any thread about this

Try searching for Controlled Residential Ventilation since that is the abbreviation for controlled residential ventilation.

Can someone tell me approximately how high the follow-up costs of a central ventilation system are?

For me, due to the KfW55 subsidy, this is the only uncertain cost factor.

Heat pump, ventilation system, and possibly photovoltaics? 3 technical maintenance-intensive devices... I would like to do without all of them if that were possible.

I would just be interested in how high the costs for such a central ventilation system are per year approximately.