How many hours of fire resistance are required for shaft enclosures in buildings with four or more stories?

Shaft enclosures in buildings with four or more stories are required to have a fire resistance rating of 2 hours. This requirement is established to enhance the safety of the building by preventing the spread of fire between floors via vertical openings, such as stairs, elevators, and ducts. The 2-hour fire resistance ensures that the enclosure can withstand fire for a significant period, allowing for safe evacuation of occupants and access for firefighting operations.

This design consideration aims to compartmentalize fire hazards and protect structural components, ultimately contributing to the overall fire safety of higher buildings. Adequate fire-resistance-rated construction is critical in multi-story buildings, where the potential for rapid fire spread can lead to increased risk for occupants and first responders.