KfW40+ with a basement inside or outside the thermal envelope?

Ok, is there a big price difference between 200mm and 140mm?

Just for completeness: it is technically possible to achieve the U-values for KfW40 basement walls also with 140 mm XPS insulation, provided you use a particularly high-quality XPS insulation board with λD = 0.027 W/(m·K). I don’t really believe your supplier has calculated it that way, because they are about 50% more expensive per sqm than the usual Styrodur & co. standard XPS boards, but you can check.

Otherwise, the difference between 140 mm and 200 mm is also about 50% higher cost per sqm – assuming your supplier passes on the material prices 1:1. It should be possible to install the 200 mm insulation in a single layer as well, so the labor costs should be the same.

Basement offer currently has 24 cm WU concrete.

You need to be careful here, if relevant: you won’t be able to do flush-mounted electrical installation in a 24 cm WU concrete wall, because the required thicknesses can no longer be adhered to. You need to consider if and how this affects you.

Ah, ok. I will discuss this with the basement builder. Thanks.

But it won’t get cheaper, because the insulation material is more expensive and the labor effort is slightly higher.

how was the construction done in the end? how thick was the insulation? was everything within the thermal envelope? which heaters were installed where?

how was the construction done in the end? How thick was the insulation? Was everything inside the thermal envelope? Which heating systems were installed where?

Hello, the basement was built inside the thermal envelope, and I am very satisfied. 12cm floor and 14cm walls. Yes, everything inside the thermal envelope. Heating: Tecalor THZ 504.