Single-family house KfW55 - Extra costs: rip-off or justified?

Where we are back to the topic of energy consumption: a Kfw55 house with double-glazed windows can of course be compared to a Kfw55 house with triple-glazed windows.

But even if both houses have the same calculated value and are used absolutely identically, there can still be noticeable differences.
As the saying goes: The journey is the destination. And there you can definitely get creative.

But even if both houses theoretically have the same value and are used absolutely identically, there can still be noticeable differences. As the saying goes: The journey is the destination. And you can get creative with that.

I find it a bit tedious now to philosophize about theoretical nuances in this thread. Especially since most, like me, are not experts here. As a summary, I take away: You advise the OP to invest, I do not. I only advise a good heating system.

For us, the surcharge from KfW70 to 55 was "only" €33,000 for a 145 m² house with a basement. That was in October 2021. For just 15 kWh/m² less energy demand... The grant was €26K back then. So it wasn’t worth it; we were even advised against it, but the ecological conscience was stronger... But nowadays there are hardly any subsidies anyway. So insulation is not worth it anymore, not even one-third as much... Better to invest in photovoltaics and batteries (controversial, I know...).

I find it a bit tedious now to philosophize about theoretical nuances in this thread. Especially since most people here, like me, are not experts. As a summary, I take away: You advise the OP to invest, I do not. I only advise a good heating system.

No, I recommend sensible planning and reasonable use of capital. KfW 55 makes sense – but there are enough energy consultants who calculate the house nicely for builders, but in the end do not deliver a corresponding result in daily (heating) energy consumption. I would like to go one step further than you with "... to a good heating system" or be more specific. The heat generator (brand X or Y) is basically irrelevant. Good planning (design temperature, hydraulic balancing, laying distances) is the be-all and end-all. Better to spend 300€ on that and "only" build KfW 70 on paper but live in KfW 55 in terms of energy consumption (because the heating, for example, only needs 28 degrees flow temperature in the KfW 70 house with good planning instead of 34 degrees in the KfW 55 house with "we've always done it that way"). That’s what I meant by calculating nicely.

instead of 34 degrees in the KfW 55 house with "we've always done it this way"

We have 40 degrees in the KfW 55 house - our construction company: "We do this standardly", 35 costs a 4500€ surcharge :p

Better to spend 300€ on that and build "only" KfW 70 on paper

I also recommend that: you don't have to chase the number. You get a very efficient house without a significant investment.