Basement insulation for KfW 55

Hello,

we have an acceptance appointment soon for our newly built prefabricated single-family house consisting of ground floor, upper floor and a basement living area (everything is to be delivered in [KfW55]-standard). The basement is made of concrete (20 cm thick), embedded in the slope with 50% underground and has 12 cm thick insulation under the floor slab and 10 cm perimeter insulation on the exterior walls. However, it is already noticeable now (before finishing) that it is significantly colder there than in the other floors.

My question: Is this insulation REALLY sufficient for a [KfW55] basement? (even if the basement has underfloor heating)?

Thank you in advance for any help!
Marcel

KFW55: Calculations have to be made. You can’t really say that in general terms. And then the basement is not considered in isolation, but the whole house. Just for your information: Kfw55 confirmation also requires construction supervision by an expert (including documentation). If you didn’t do that during the basement construction, it will already be very difficult to confirm this!

KFW55: Calculations need to be done....

That might be a bit late.
In addition, many often forget the equivalence certificate of the WB.

Best regards.

You can already tell now (before the expansion) that it is significantly colder there than on the other floors.

No way!

Is it really cooler in the basement in summer than under the roof? There must be a defect!!!

My question: Is this insulation REALLY enough for a KfW55 basement?

You probably didn’t buy a KfW55 basement but a KfW55 house... In other words, it depends on how the entire house is insulated etc.

It is quite normal that the basement is not built with the same insulation thicknesses as the above-ground part, because the outside temperatures are completely different here. In the soil, you never have temperatures of -10° or -20°... accordingly, the heat losses through the basement walls are lower, even if they are less well insulated...