Single-family house U-values good or rather not?

Hello,

Since a KfW 55 house was ordered turnkey, it is of course guaranteed in writing ;-)

This is often the case on paper, but if you take a closer look in practice, it can sometimes become unclear.

...The primary energy demand depends on the chosen heating system,...

not only that, the thermal quality of the building envelope also plays a role. Therefore, two parameters must be met for the respective KfW efficiency levels. Theoretical primary energy is rather secondary for the operator; what counts for them is the final energy considering the real conditions of the specific construction project, not the standardized Energy Saving Ordinance reference parameters!
Therefore, it is not permitted to dimension heating systems based on the Energy Saving Ordinance or KfW results or to make consumption statements!

..., of course I don’t find that so cool now :/

Whether "cool" is a suitable criterion for a significant investment decision is something everyone has to judge for themselves ;-)

Best regards

For me, it has always been the case that with, for example, 55, you only consume 55 out of 100 of primary energy for that very house.

Replace energy with primary energy. That is a significant difference. Especially when it comes to what you end up paying ;)

...Replace energy with primary energy. That is a not insignificant difference. Especially when it comes to what you end up paying ;)

The economic significance of primary-energy-defined Energy Saving Ordinance or KfW efficiency levels for the individual operator, in my opinion, is insufficiently communicated or presented. Whether consciously or not, I leave that open ;-) Decisive for the individual operator is always the payable, actual final energy, not a theoretical construct "primary energy" on paper! The previous definitions, strictly speaking primary energy, only allow a qualitative assessment. Energy Saving Ordinance standard is permissible, KfW 70 somewhat better, KfW 55 or 40 each still somewhat better! That primary energy factors have a market-political leverage function, and that lobbyists may have "helped" here, will not have escaped intelligent builders ;-) Anyone who builds a PH at the Upper Rhine is economically just as misguided as someone who builds an Energy Saving Ordinance standard on Zugspitze :-) A theoretically achieved KfW status does by no means automatically guarantee profitability for the individual construction project, especially since a significant number of construction projects in practical execution partly deviate considerably from the "paper form". The one who suffers is usually the inexperienced builder, who usually has taken on heavy debt. Subsequent "healing" is rarely possible, and then usually only with limited success. Timely prevention is therefore always cheaper than subsequent attempts at healing! Best regards