KfW - construction: is it necessary or not?

...Aha. Then prove your claim that KfW-55 is cheaper to build than the Energy Saving Ordinance with exactly those. Even KfW itself mentions ~10% additional costs here. Which, by the way, I can confirm to that extent, as I had my construction project offered as KfW 70 (Energy Saving Ordinance), KfW 55, and KfW 40.

Ahh, I am very interested in that! We are deciding here based on a "gut feeling" What was the result in numbers (differences) and according to which standard did you build?

@MayrCh

ISE:
...approx. 0.3 percentage points per year on averages of about 17.5% [ISE10] and peak values of 22%.

The evidence is further up with several current projects.
Specific numbers are also given there.

Since you have been offered a KfW70 house,
you are referring to the old KfW conditions regarding the 10%.
It is known that more insulation is often sold at a high price, even though this only concerns the insulation material.

Ahh, that interests me a lot! We decide here based on our "gut feeling" What was the result in numbers (differences) and according to which standard did you build?

Mention missed. Additional cost KfW 70 -> KFW 55 would have been about ~5%, I believe ~15k€. For about €100 heating cost savings per year. This would only have paid off thanks to subsidies (which we all pay for). So in my opinion, in my specific individual case, neither economically nor financially reasonable. KfW 40 would then have been >>10% more.

Old standards with the old subsidies which no longer exist bring nothing in comparison to current projects.

A construction cost comparison certainly not, because price increases are currently far too high. Even a change of year achieves the 10%, see BKI.