Insulation of basement floor slab, a requirement for KFW 70?

Hello, We want to build a single-family house this year and are considering various financing options. So far, we do not know whether we want to take out a KfW loan. Is insulation below the basement floor slab mandatory for a KfW70 standard if the rest of the house is well insulated and the heating of the house is connected to the district heating system from my parents' wood chip heating? According to the offer, insulation would cost €2400 in our case. My consideration is therefore whether this additional cost is worth it for a €50,000 loan at a better interest rate? What do you think about it?

Hello,

Is insulation beneath the basement floor slab mandatory for a KFW70 standard if the rest of the house is well insulated and the heating of the house is supplied via a district heating connection to my parents' wood chip heating system?

This cannot be answered in general terms; the key figures of the district heating would have to be known for this; meaning, the expert has to calculate. Is it even guaranteed that you are allowed to connect there with your construction project? Municipality - capacity?

Insulation would cost €2400 in our case according to the offer. My consideration is therefore whether these additional costs are worthwhile for a €50,000 loan at a better interest rate? What do you think about that?

Basically, it can mostly be stated that a reasonable building envelope - whether monolithic or with ETICS - as well as an air-to-water heat pump lead to KFW 70 ... unless the new building is to be constructed on the Zugspitze.

You can also achieve KfW 70 with the 15% rule, which means more insulation. Insulation beneath the floor slab is mostly required starting from KFW 55.

Rhenish greetings