Since humans make CO2, CO2 levels in spaces work as proxy for air transfer with outside.
So high CO2 but no headaches probably rules out low oxygen level, since humans consume oxygen so low air transfer would reduce oxygen levels.
Instead most likely explanation is that there is something that gets discharged into air from new buildings but not (all) old buildings that causes problems unless enough air exchange with outside.
Back when i had asthma, it would go fully away when travelling to southern europe with their leaky walls.
Since humans make CO2, CO2 levels in spaces work as proxy for air transfer with outside.
So high CO2 but no headaches probably rules out low oxygen level, since humans consume oxygen so low air transfer would reduce oxygen levels.
Instead most likely explanation is that there is something that gets discharged into air from new buildings but not (all) old buildings that causes problems unless enough air exchange with outside.
Back when i had asthma, it would go fully away when travelling to southern europe with their leaky walls.