Cross-ventilation - is it mandatory in apartments?

So for us it has been great since mid-June that we can ventilate across the house at night. So significantly more than the 5-10 days a year. And whoever boasts loudly here has their underfloor cooling running permanently. Without cooling, be it air conditioning or FBK, the world looks different again, you have to work with the heat storage of the house and cool it down overnight. Controlled residential ventilation is a nice thing, but by far not the required scale

Open a terrace/balcony door on the ground floor and in the attic... I even let the air flow in and out on the same side of the house

Have fun trying that in an apartment building...

It's certainly not a miracle cure - but the ventilation has contributed at least as much to the stability of my marriage as the navigation system in the car and the resulting elimination of route discussion, due to the removal of all ventilation arguments.

I preferred to find the right partner ;). We agree on this: weather reasonably good = window open.

Have fun in the first winter without ventilation with heat recovery...

And whoever boasts so much here has their underfloor cooling running permanently. Without cooling, be it air conditioning or underfloor cooling, the world looks different again; you have to work with the house's heat storage and cool it down overnight. Controlled residential ventilation is a nice thing, but by far not the required scale

No, I switch it on via Home Assistant and it only runs at maximum values above 26 degrees. Otherwise, it is regulated by the combination of construction, ventilation, and shading.

We have all the windows on one side in our current newly built apartment (built around 2018/19) as well. That works quite well so far, only it's really difficult to get the heat out again in the summer. Also, because we live right in the city center and not much wind passes by here. I would never do it like that with owner-occupied property, but it's okay for renting. You also don’t really get rid of humidity quickly in the summer that way, which is a bit annoying. But to answer your question, it also doesn't seem to be required in NRW.