>Meanwhile, the global energy crisis of the 1970s incentivized architects and engineers to design buildings that were increasingly airtight — why pay money to h

>Meanwhile, the global energy crisis of the 1970s incentivized architects and engineers to design buildings that were increasingly airtight — why pay money to heat a building just to see that heat escape out a crack around a window? That, in turn, required new approaches to controlling their interior climates. Mechanical systems for heating, ventilation, and air conditioning (HVAC) became more common, as did open-plan layouts to allow for better air circulation. The flip side of this process is that residential windows became smaller, reducing not only natural light but ventilation. Apartment buildings changed from layouts with lots of windows and cross-ventilation to maximizing the footprint on the lot. Perhaps more efficient for heating/cooling, but also traps a lot more polluted indoor air. It is startling that today in the US there are a high number of residential units with gas ranges/ovens but very little or no ventilation.