48 gas concrete, triple glazing, photovoltaic, ventilation system - KfW 40

Hello,
our architect planned our house with the following things:

48 cm aerated concrete, triple glazing, insulation between rafters, 60 mm insulation above rafters, central ventilation system, photovoltaic system and now we only achieve KfW 55 standard. Allegedly, the building envelope would not be sufficient for KfW 40.

Does anyone have experience with this? Thanks for your support.

"Allegedly" is not a suitable indicator. This is to be calculated in black and white. Then you can also see where you still need to intervene in order to reach the required target value. It can't really be that far off anymore.

I see it similarly. Of course, you have left out all relevant properties such as:

[*]What is the insulation value of the aerated concrete blocks?
[*]What is the insulation value of the windows?
[*]What is the insulation value of the cavity and counter-batten insulation?
[*]How efficient is the ventilation? (But this is also irrelevant for the building envelope.)

Overall, with the given key data, one would expect something towards KfW 40, maybe just above it, so that it really only fails due to details. A calculation would reveal this.

Here are the values for the materials:
Porenbeton: lambda 0.09
Holzfaserplatte: 0.048
Zellulosedämmung: 0.04
Window: Uw 0.95
Thermal bridges are assumed at 5%

With Porenbeton lambda 0.08 we would have met the criteria, but we did not want such a soft stone.

Could it be that something was done wrong in the calculation?
Can I have the calculation checked somewhere else?

Windows: Uw 0.95

But that is currently not state of the art. Actually even bad for a new build.

But that is currently not state of the art. Actually even bad for a new building.

wait ... with plastic windows I get: Uw 0.84

better?