I am not building a semi-detached house, but with a comparable wall structure (Ytong blocks with 36.5 cm, lambda 0.09 W/m*K). KFW55 is basically possible with this, but an appropriate building services technology (controlled living space ventilation as well as at least an air-water heat pump) must be present. In addition, a thermal bridge calculation as well as the thermal bridge optimization underlying it must take place.
Without thermal bridge optimization, I would not achieve KFW55 - not even with a 42.5 cm block.
That is interesting. What does thermal bridge optimization mean?
Building services technology is not a problem. We have an air-water heat pump and controlled living space ventilation. The structural engineer sees no problems with this for us. Maybe thermal bridge optimization could possibly help.