New construction according to the 2016 Energy Saving Ordinance no longer possible without a ventilation/exhaust system?

Unless the demand is not calculated (from volume, orientation, window area, countless factors...) but built based on reference values without calculation. As mentioned above. THEN controlled residential ventilation is mandatory. And yes, even with the calculation method, it can be difficult with a construction type made of stone without controlled residential ventilation, but according to reports on the internet, it is quite possible. With wooden houses anyway, since that is almost standard?

THEN controlled residential ventilation is mandatory.

With the restriction that not all combinations require heat recovery, only central exhaust systems do. But whether this is so relevant in practice... I mention it only for the sake of completeness.

But: Why the reference value method. Then the combination is open.

Additional Requirements for a KfW Efficiency House 40 Plus
A KfW Efficiency House 40 Plus meets the requirements of a KfW Efficiency House 40 and includes the following plus package:

[*]A power-generating system based on renewable energies
[*]A stationary battery storage system (power storage)
[*]A ventilation system with heat recovery
[*]A visualization of power generation and power consumption via a corresponding user interface

Only for KfW 40 Plus is a controlled residential ventilation with heat recovery explicitly mandatory. Otherwise, one could also do without the exhaust air system. You just have to calculate like and .

Probably small homebuilders do not want to/"cannot" do this; therefore, they only have the proof according to reference values in mind.

There is a lot of arguing here again, that you "must" not ventilate thanks to [Kontrollierte-Wohnraumlüftung]. Sounds as if ventilating were a terrible burden. I only know my/our living behavior, but basically we always have windows open in the bedrooms when we/child are inside. From spring to autumn also in many other rooms.

I only know my/our living habits, but we basically always have the windows open in the bedrooms when we/the child are inside. From spring to autumn also in many other rooms.

Do you also keep the windows constantly open in winter when someone is in the room?

Predominantly. Not every hour of the night and not at double-digit minus temperatures, but still very regularly. We sleep well in cool, clear air.