Stair Width for Existing Office Building
A five-story office building (B occupancy) is being renovated. Each floor has an occupant load of 400 based on the proposed layout. The building is fully sprinklered. The building has two exit stairways: one is 44 inches wide, and the other is 36 inches wide. The owner wants to keep both stairs as the required means of egress. The building official notes that the 36-inch stair is narrower than the 44-inch minimum required for new construction, but the building is existing. The owner argues that since the building is sprinklered, the 36-inch stair is acceptable as a second exit. The building official must determine if the 36-inch stair can be counted as a required exit for the proposed occupant load. The renovation does not change the occupant load from the existing use, but the owner is increasing the density of workstations. The code requires that each exit serve at least 50% of the occupant load. The building official must calculate the required egress width and evaluate the compliance of the 36-inch stair.
1. Calculate the required egress width for the stairs and determine whether the 36-inch stair can serve as a required exit for 400 occupants per floor.
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Under IBC Section 1005.3.1, the required egress width for stairways in a sprinklered building is 0.2 inches per occupant. For 400 occupants, the total required stair width is 400 × 0.2 = 80 inches. Because two exits are required, IBC Section 1007.1.1 requires that each exit serve at least 50% of the occupant load. Therefore, each stair must handle 200 occupants, requiring 200 × 0.2 = 40 inches of width. The 36-inch stair provides only 36 inches, which is less than the 40 inches required for its share. The 44-inch stair provides 44 inches, which is sufficient for 220 occupants (44/0.2 = 220), so it meets its 50% share. Although the total width of 80 inches equals the total required width, the 36-inch stair cannot be counted because it violates the 50% rule. The building official must reject the use of the 36-inch stair as a required exit for 400 occupants per floor.
2. What options does the owner have to achieve compliance without widening the 36-inch stair?
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The owner has several options. First, reduce the occupant load per floor to 360 or less. At 360 occupants, each exit must serve 180 occupants, requiring 180 × 0.2 = 36 inches, so the 36-inch stair would exactly meet the minimum. Second, add a third exit stairway or an approved horizontal exit that can serve part of the occupant load. Third, provide an exterior ramp or an exit passageway that supplements egress capacity. Fourth, widen the 36-inch stair to at least 40 inches. Fifth, if the building is existing and the renovation does not increase the occupant load, the owner might request a variance or use existing building provisions under IBC Chapter 34, but any change of occupancy or increase in occupant load would likely require full compliance. The building official should require a revised egress analysis and plans before approving any alternative.