Is 30 cm aerated concrete sufficient for a KfW 70 house?

At the beginning of February, we want to start building our single-family house (solid stone). It is supposed to meet the KfW 70 standard. Our developer has suggested 30 cm aerated concrete for the exterior walls in "monolithic construction" plus a two-layer mineral plaster with a thickness of 15 mm. We have no knowledge of the subject at all and are now wondering whether this wall construction can meet the KfW 70 standard. The stone does not have a particularly good U-value after all.

Have the thermal insulation calculation shown to you; it clearly states whether the wall structure is sufficient for a KfW70 house. But it is not only the exterior walls that determine thermal insulation, also windows, roof, basement. A rather poor exterior wall for KfW70 can also be justified there. If you want to be absolutely sure, submit the Energy Saving Ordinance calculation to an independent energy consultant for review. This costs a fee, but then you can be really sure.

Upon inquiry regarding the thermal insulation calculation, my developer just shrugged and referred to his "many years of experience." It would "work out"... I will add the money and hire an energy consultant to carry out the inspection.

Hello again, the developer must provide proof, the Energy Saving Ordinance stipulates this - and it has the character of a law. In addition, the KfW increasingly checks compliance with the conditions for the individual funding measures. If the calculations are incorrect, the funding is lost and - if things go badly - a fine is due.

That’s exactly right, if serious mistakes are made here, it will cost a lot of money. The [Energieeinsparverordnung] must be correctly complied with here. I would not agree to anything else.

I also think that what some developers get away with is really shocking. They just shrug their shoulders and say, it will be fine. The client then has to cover the additional costs. But that is without their concern.