Build a single-family house as KfW55 or Efficiency House 70?

For us, that was not an option anyway, so we will also stick to KfW55, but she vehemently criticized KfW55 and also the air-to-water heat pump, which seemed strange to us.

We had similar experiences. My advice at this point is to only build with someone who reasonably supports your wishes. Otherwise, some things will be done half-heartedly, poorly, or too expensively due to lack of experience or commitment.

Personally, I find insulation to KfW 55 a sensible goal, whether you take the few euros of subsidy or just miss it. "KfW 55" is an easy-to-communicate target for the insulation standard, and many providers should have something suitable ready. With an air-to-water heat pump, the technical side is fulfilled anyway; there is no need to discuss it further.

So out of 10 general contractors requested, 10 built with Ytong. And the only reason is the cost advantage.
For an architect, that then plays a minor role.

That may be a regional focus.

Our house (KFW 55) would have cost about €25,000 more monolithically. NRW. There are several KS plants here.
Don’t underestimate the logistics. A neighbor has Wienerberg Poroton with perlite, his shell construction cost twice as much, although it is “only” 20% larger. But several trucks have to travel across the country for that. Also a factor.

My experience is rather that the ETICS is cheaper than the monolithic wall construction with the same insulation standard. Regardless of whether KfW 55 or 70.

It was the same with all my quotes that monolithic construction incurred an additional cost.

We build regionally with a two-layer system using Ytong and mineral wool, and without a basement. The surcharge for 2 cm thicker insulation and possibly additional insulation under the slab is low, about the amount of the subsidy. However, the additional insulation does not bring much more benefit since construction already exceeds the Energy Saving Ordinance standard by a good margin. It also depends on which standard you refer to. "Only" the Energy Saving Ordinance would be insufficient for me, especially in colder regions in Germany. However, you will not recoup €20,000 if that is truly the real cost and not just claims or defensive offers.

That may be a regional focus. Our house (KFW 55) would have cost about €25,000 more monolithic. NRW. There are several KS plants here. Don’t underestimate the logistics. Neighbor has Wienerberg Poroton with perlite, his shell construction cost twice as much, and it is “only” 20% larger. But several trucks have to cross the republic for that. Also an aspect.

OK, the regional aspect may be. I have an offer for the shell construction and the position of the exterior masonry with Poroton costs including production €16,000. For 10x10m two-story. That corresponds to KFW 55. What more could you save there? Must admit everything is simply cheaper for us.

Which once again reinforces the saying that the devil always sh*ts on the biggest pile, because it ultimately means that the subsidy is a nice extra for those who do not need it - which, in my opinion, calls into question the purpose of a subsidy aimed at private individuals (even below the social insurance threshold).

It's a shame that you understand me so differently than I mean. I'll put it differently: Don't buy anything you don't need or want just because it is subsidized.