Economic efficiency construction costs vs heating costs

Can I sign off on this ;-)
So if the 10 T€ are supposed to be your buffer, you should definitely not allocate them.

Maybe they have some left over for buffers. But since some things cost more over time (or can cost more, here a bit more stainless steel... etc pp) Otherwise, it basically makes sense overall to invest in insulation or solar, as that lowers operating costs and possibly increases resale value. Controlled residential ventilation is also not bad for increased comfort.

As said, this is only about the heating.
For the other "trades" there is still enough buffer available. And our financing has also been chosen very securely. We can save or invest a considerable amount every year. Photovoltaics, outdoor facilities, exterior plaster, carport, garden house, attic expansion, etc. can all be done a bit later. Nevertheless, we have planned and financed so that everything could be completed.

Waiting is not an option; once the wall is up, it stays ;) Everything else can still be influenced.
We already have a small credit balance at the shell construction stage even though the foundation is €3000 more expensive than expected.

However, I am also aware that this can change quickly. If that happens, it is our fault, because we decide which materials are to be used. So it is a matter of discipline.

But I still wonder how to minimize the risk of not spending everything at the beginning and having nothing left at the end. Or if you saved in the wrong place. Who knows?

As I said... grab your building geometry and calculate back and forth with the U-value.

I generally believe you can be sure that the pricing of the BTs, GÜs, and GUs is such that the additional investment tends to pay off late - or rather not at all - they simply don't want to deviate from their standard or want to maximize profit (it's quite similar with electrical appliances - going from A++ to A+++ rarely pays off). If you do single awarding, however, it might look a bit different.

The result of all my research was that any investments in the future for our building project are not worthwhile. Therefore, I did what I wanted and does not have to pay off.

Gas --> Because it is simply easy to install, makes no noise, and is uncomplicated and cheap.

Controlled residential ventilation --> No one can really ventilate properly in reality, and stuffy air causes headaches.

Windows --> Triple-glazed, because it had to be due to the HLB and somewhat better at sound insulation.

Solar thermal, photovoltaics, heat pump, better insulation --> would have all cost more but would not bring me any improvement in living quality.