A house under €140,000?

A residential building must be constructed according to [Energieeinsparverordnung]-guidelines, yes

Energy Saving Ordinance 2016 must be complied with.

Edit: ypg was faster.

Does someone actually come by and check that, or how does that work?

As a rule, rather not; if so, it’s mediocre – especially since the insulation isn’t exorbitantly expensive now and even more or less pays for itself. I just went to the building authority and asked if I had to report something as completed, and the official said that we should inform the land registry office at some point, but otherwise no one else comes by anymore (though that may vary).

Does he have to build a house according to today's standards, is that mandatory? I always thought it basically only concerns KFW loans. With smaller amounts and the current interest rate, it's "almost" irrelevant.

I didn't quite figure that out at first either. Every house has to comply with the Energy Saving Ordinance. For that, the thermal insulation certificate is prepared before construction begins.

For KFW funds, the energy certificate is additionally required, which is created when the house is finished. Here, the minimum requirements of the Energy Saving Ordinance are then exceeded.

At least that's my understanding. We consciously forgo KFW and therefore don't need an energy certificate.

Does someone actually come by and check that, or how does that work?

As far as I remember, the required data is in the building application, which has to be approved. And before the next question is asked: yes, you build the house that was approved after the approval.

If I ever consider writing a book like "House Building for Dummies," I will explicitly check what belongs in the building application :)