What is a required fire-resistance rating for shaft enclosures connecting four stories or more?

A fire-resistance rating of 2 hours for shaft enclosures connecting four stories or more is based on building codes designed to enhance life safety and property protection in multi-story structures. The rating reflects the ability of the enclosure to withstand fire conditions and limit the spread of flames and smoke between floors.

Shaft enclosures are critical for the safe evacuation of occupants and for protecting building components, ensuring that emergency services can access upper levels safely during a fire incident. The 2-hour rating provides sufficient time for occupants to evacuate and for firefighters to intervene, which is essential in larger buildings where the risk of fire can be more significant due to increased vertical travel and fuel loads.

This requirement aligns with various building and fire codes, which often specify fire-resistance ratings based on occupancy types, building heights, and the number of stories involved. Choosing a rating lower than 2 hours for a shaft enclosure could compromise safety by allowing smoke and flames to penetrate more quickly, undermining the effectiveness of the enclosure during a fire emergency.