Is a surcharge of 17,000 common for KfW55?

Sure, you could have the energy consultant calculate it, but that’s not exactly cheap.

I think this can definitely be expected within the scope of preparing the (preliminary) thermal insulation certificate. In the end, it’s just a few clicks in the tool to find out how much thicker the insulation on walls, floor, roof needs to be or whether the glass needs to be a bit better. This can certainly be priced indicatively. Or if you’re building with a general contractor/contractor, simply have the building offered according to the Energy Saving Ordinance and KFW 55.