Stack effect

The stack effect can be useful to drive natural ventilation in certain climates, but in other circumstances may be a cause of unwanted air infiltration or fire hazard.

[1] In a modern high-rise building with a well-sealed envelope, the stack effect can create significant pressure differences that must be given design consideration and may need to be addressed with mechanical ventilation.

Stairwells, shafts, elevators, and the like, tend to contribute to the stack effect, while interior partitions, floors, and fire separations can mitigate it.

[3] The stack effect can also exacerbate the spreading of fire, especially in tall buildings where design flaws allow the formation of unwanted drafts.

[4] The latter of these was in part exacerbated by the stack effect, when a cavity between the outer aluminium cladding and the inner insulation inadvertently formed a chimney and drew the fire upwards.

Examples of traditional usage include the wind towers common in Middle Eastern architecture, which capture and direct cooler breezes into the building while expelling hot air to maintain comfortable indoor temperatures.

By carefully designing the building's structure, orientation and ventilation paths, architects can leverage the stack effect to reduce reliance on mechanical cooling systems and improve overall energy efficiency.

The net negative pressure on lower floors can induce outdoor air to infiltrate the building through doors, windows, or ductwork without backdraft dampers.

Consequently, cool air will travel vertically down the building through elevator shafts, stairwells, and unsealed utility penetrations (i.e., hydronics, electric and water risers).

Once the conditioned air reaches the bottom floors underneath the neutral axis, it exfiltrates the building envelopes through unsealed openings such as through dampers, curtainwall, etc.

Large temperature differences between the outside air and the flue gases can create a strong stack effect in chimneys for buildings using a fireplace for heating.