House costs per KFW level per m²

Well, if you're already willing to accept a penalty, you might as well just build KFW40. It's not that much more expensive and with subsidies as well as savings, it balances out significantly. A few square meters less or, for example, a omitted chimney offer considerably more saving potential!

After the elections, it might even happen that you won't be allowed to build anything worse anyway. ;-)

don't get hung up on KfW40, a plot with a house only works that way. It could also be €100,000 cheaper or more expensive. This is now the chance for the house. Calculate the house to fit you based on the area and equipment.

We don't want to simply build KFW 40 now, although we can't afford it.

If it really means "if we know that the fun is too expensive for us," then keep looking elsewhere or play the luck that your points will suffice without it. If it actually means "although we don't know if we can afford it," that relativizes it. I don't think that the additional effort for the KfW40 energy standard will break the financing or shrink the living room into a rabbit hutch. Maybe the car will have to sleep without a pergola over it, so what. If there is no commitment to a general contractor who is too expensive with KfW40, then you take the "risk" of KfW40. I just think it's something that shouldn't be prescribed to normal earners as if we all drive Porsches. Apply, roughly plan the house here already, and then ask the local builders whether the surcharge for KfW40 effectively consumes the carport, or the fireplace, or the corner windows, or the brick cladding. Without a basis, philosophizing alone won't get us "calculably" settled.