What specifically causes the stack effect in buildings?

The stack effect is primarily driven by the relative buoyancy of hotter air. As air heats up, it becomes less dense and rises within the enclosed spaces of a building. This phenomenon occurs because warmer air, being lighter, naturally ascends, creating a pressure difference between the lower and upper parts of the building. When warm air escapes from the upper levels (for example, through vents or openings), it creates a negative pressure that pulls in cooler, denser air from below.

This process can lead to significant air movement throughout a building, impacting energy efficiency, comfort, and indoor air quality. It is particularly notable in tall structures where the height exacerbates the difference in pressure and temperature, intensifying the stack effect. Understanding this concept is vital for building analysts to develop strategies for managing air flow and optimizing energy performance in buildings.