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

KalterKaffee schrieb:

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

Just for completeness: it is technically possible to meet the U-value “target values” for KfW40 basement walls even with 140 mm (5.5 inches) XPS insulation, provided you use a particularly high-quality XPS board with a thermal conductivity of λD = 0.027 W/(m·K). I don’t really think your supplier has priced it that way, as these are about 50% more expensive per square meter than standard Styrodur & similar XPS boards, but you can check.

Otherwise, the difference between 140 mm (5.5 inches) and 200 mm (8 inches) is also about a 50% cost increase per square meter—assuming your supplier passes material costs directly. It should also be possible to install the 200 mm (8 inches) insulation in one layer, so labor costs should be the same.

Basement quote currently has 24 cm WU concrete.

You should be careful here if relevant: you won’t be able to do flush-mounted electrical installations inside a 24 cm (9.5 inches) WU concrete wall because the required wall thicknesses can no longer be maintained. You need to consider if and how this affects you.

Ah, ok. I will talk to the basement builder about this. Thanks.

It won’t get cheaper, though, since the insulation material is more expensive and the labor effort is slightly higher.

@KalterKaffee How was the construction completed in the end? What was the thickness of the insulation? Was everything included within the thermal envelope? Which heating systems were installed, and where?

M a v o schrieb:

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

Hello, the basement was built within the thermal envelope, and I am very satisfied. 12cm (5 inches) insulation on the floor and 14cm (5.5 inches) on the walls. Yes, everything is inside the thermal envelope.
Heating: Tecalor THZ 504.