KFW 55 - Semi-detached house - Not possible?

Hello everyone,

we are currently planning our semi-detached house.

Our semi-detached house is planned with 8 x 12 meters (12 meters is the side facing the neighbor) - 2 full floors, converted attic, basement. We want to build with brick (basement with white tank). Now a thermal insulation certificate has been calculated - also with regard to whether KfW 55 is an issue. The calculation was done with a 36.5 brick with lambda 0.09. Unfortunately, the transmission heat loss is still much too high for KfW 55. Even with a brick that, in my opinion, is great like S7 with 0.075 lambda, I would have no chance to reach KfW 55 (thickness 36.5). I would only reluctantly take a thicker brick, as that would reduce the living area.

Apparently, the A/V ratio is relatively poor with our semi-detached house.

Does anyone know such problems? Is KfW 55 more difficult to comply with in semi-detached houses or which adjustment options would need to be considered?

Thanks in advance for comments!

Hello,
we have built (had built) a semi-detached house, 6.5 * 11m and KfW 55. Also with a basement, 2 full floors and an attic converted to living space. Our wall construction is aerated concrete - insulation - plastered aerated concrete or aerated concrete - insulation - clinker. Total wall thickness 44cm. So it should not be a general problem. For an extra charge (which was too high for us) we could have also gotten a KfW 40 house. By the way, our semi-detached house partner built with another company, so that didn’t matter.
Best regards

The ratio of external envelope/area to volume has only limited impact, since the underlying reference house for the calculation is always configured in exactly the same favorable (or unfavorable) way.

We have almost the worst A/V ratio and still KFW55. (Single-story, with setback floor without basement)

Ad absurdum: the glass house.

According to which energy saving ordinance have you built or are you building? We have to build according to the energy saving ordinance that has been valid since 2016.

I am not building a semi-detached house but with a comparable wall structure (Ytong blocks with 36.5cm, lambda 0.09 W/m*K). KFW55 is basically possible with this, but a corresponding building technology (controlled residential ventilation as well as at least an air-water heat pump) must be present. In addition, a thermal bridge calculation as well as the corresponding thermal bridge optimization must take place.

Without the thermal bridge optimization, I would not achieve KFW55 - not even with a 42.5cm block.