Airtight buildings are perfectly fine with a proper Heat recovery ventilation system (HRV) that they should be using. HRV's are mandatory when building the PassiveHaus spec.
True. Unfortunately, at least around here a lot of buildings have been built in the past five or so decades that are fine insulation-wise but sorely lacking in ventilation, natural or otherwise, leading to widespread health issues. Many prefab concrete buildings from the 60s and 70s, even 80s, are practically ready for demolition.
