The minimum fire-resistance rating of enclosures for interior exit stairways and ramps, connecting less than 4 stories, must be:

The minimum fire-resistance rating for enclosures of interior exit stairways and ramps that connect less than four stories is set at 2 hours. This requirement is based on life safety considerations, ensuring that occupants have adequate time to safely evacuate the building in the event of a fire. The 2-hour rating provides a protective barrier, limiting the spread of smoke and flames, thus enhancing the overall safety of the exit strategy for individuals within the building.

Choosing a higher fire-resistance rating, such as 3 or 4 hours, would exceed the minimum requirements but may not be practical or necessary for structures of this size and height. Conversely, a 1-hour rating would not offer sufficient protection for the occupants in the event of an emergency, thus does not meet the established safety standards. The code specifies these ratings to balance safety with practicality in construction and design.