What is the minimum fire resistance rating for the enclosure of floor openings connecting four or more stories in new construction?

According to NFPA 101, Life Safety Code, the protection of vertical openings is critical to prevent the spread of fire and smoke between floors. The required fire resistance rating for the enclosure of these openings is determined by the number of stories they connect. For new construction, when a vertical opening, such as a shaft for an elevator or stairway, connects four or more stories, the enclosure must be constructed with materials providing a minimum fire resistance rating of 2 hours. This more stringent requirement for taller buildings helps to ensure the integrity of egress paths and compartmentalize the fire for a longer duration.

A. 1 hour: This is the minimum fire resistance rating required for enclosures of vertical openings connecting three or fewer stories in new construction, not four or more.

B. 1½ hours: This rating is typically associated with specific fire door assemblies or other components but is not the specified minimum for an enclosure connecting four or more stories.

D. 2½ hours: This rating exceeds the minimum code requirement for this application and is therefore incorrect as the minimum standard.

1. National Fire Protection Association. (2021). NFPA 101: Life Safety Code. Quincy, MA: NFPA. Section 8.6.5.1, "The enclosure for a vertical opening connecting four or more stories in a new building shall be of construction having a fire resistance rating of not less than 2 hours."

2. National Fire Protection Association. (2021). NFPA 5000: Building Construction and Safety Code. Quincy, MA: NFPA. Section 8.12.4.1, "Where a vertical opening connects four or more stories, the enclosure shall have a fire resistance rating of not less than 2 hours."

3. Cote, A. E. (Ed.). (2021). Life Safety Code Handbook (2021 ed.). Quincy, MA: National Fire Protection Association. Commentary on Section 8.6.5, "The 2-hour fire resistance rating for enclosures of vertical openings that connect four or more stories is based on the increased life safety risk in taller buildings."