Stayed at a beautiful new house in Finland, with five people instead of the usual two, the CO2 detector intermittently went off while we were sleeping. Which the hosts assured us was a faulty detector. They also spoke to how extremely energy efficient the house was, to us it seemed like there wasn't enough ventilation, to improve the insulation. Against their wishes, I slept with all windows fully cracked, which was only ~2 inches due to the "efficient" design.

How modern? We built or house in Belgium in 2016, and it was completely sealed, very well insulated, but the air quality was good because we had mechanical ventilation. Clean air blown in, stale air extracted which then went through a heat exchanger.

The only issue this house had was it overheated. We had glass facing south. Even in winter it instantly became too hot.

> I think modern domestic houses its the opposite. At least in Netherlands insulation is such a strong focus, due to climate change I think, that modern appartments have terrible ventilation

The link I pointed to is all about ventilation, so just because people ignored an important component of building science, and focused on one aspect, does not invalidate it.

And while climate change is important and using efficiency to deal with it is useful, the thermal control layer is actually the least important of the four:

* https://buildingscience.com/documents/insights/bsi-001-the-p...

'Bulk' water (precipitation) and moisture can cause deterioration of the building materials (rot, crumbling), and also mold, which has its own health effects. Leaky houses can often blow conditioned air at much faster rates than thermal leakage.

Heat recovery ventilation is the answer to this. You also get the benefit of being able to filter it.

A friend of mine recently moved to a modern apartment, built only a few years ago to a very high isolation standard (Germany). I stayed over night and slept on his couch, the air got really really dry and stuffy. It was really uncomfortable.