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# Vertical Ventilation Only after they have regarding these matters can the IC order an HVAC or smoke-control system to be used. ## Vertical ventilation Opening the top of the building is the easiest type of ventilation to understand. Unfortunately, it is often very difficult to accomplish. In an...

# Vertical Ventilation Only after they have regarding these matters can the IC order an HVAC or smoke-control system to be used. ## Vertical ventilation Opening the top of the building is the easiest type of ventilation to understand. Unfortunately, it is often very difficult to accomplish. In any discussion of high-rise ventilation, the term *stack effect* will soon pop up. An understanding of *stack effect* and how it relates to both vertical and horizontal venting will simplify the IC's decisions. The *stack effect* is the natural movement of air within a building. It becomes noticeable in buildings more than 60 ft high and becomes stronger as the building gets taller. It occurs in these buildings 24 hours a day, 365 days a year. It is caused by warm air rising up through stairways, elevator shafts, utility chases, and all other vertical shafts. If it is cold outside, the air at the top of these shafts tends to move out across the upper floors and out of the building. This is normal *stack effect*, and it can be a very powerful force in very large buildings (fig. 18-20, left side). In this case, opening or breaking a window on an upper floor would likely be beneficial, allowing smoke and gases to escape.