House costs per KFW level per m²

Nanana, you can't say that so generally. If a controlled residential ventilation system is explicitly desired anyway, then it is quite possible to take the upgrade from 55 to 40 with the additional subsidies.

At least I have not yet come across the fact that with KfW55 plus controlled residential ventilation you could already make the jump to KfW40; usually something still has to be changed in the wall structure - and then the question is: what?, and how well does the builder handle that in practice.
Yes, I do think that KfW40 is as "useful" as an organic label: you pay more, but - admittedly, I say this as a meat eater - you do not taste the extra cost. Ergo, it is something for people who want and can afford a Greta conscience - the latter is not exactly easy on the average skilled worker's wallet, but they also have to dip into their vacation fund a bit.

And in solid construction, this is certainly not achievable either.

Additional cost perimeter insulation = €5,568
Additional cost roof insulation = €1,166

Where should the perimeter insulation go? Basement slab? KG-ceiling? Surcharge for roof insulation 10 €/sqm :rolleyes: