Fire-Resistance Rating of an Existing Wall in a Change-of-Occupancy
A two-story, 12,000 sq ft building changes from office (Group B) to a congregate living facility with sleeping units (Group R-2). The existing floor/ceiling assembly between floors is wood joists with a gypsum ceiling below and wood subfloor above; the drawings show no rating. The stair enclosure is open to the corridor on the first floor and enclosed on the second. The building has a sprinkler system but the designer proposes to delete it to save cost, arguing the new occupancy has fewer occupants per square foot. The building official requires a code analysis of the change of occupancy, including the required separation between the R-2 and any remaining B space on the first floor, and the stair enclosure rating.
1. How should the change of occupancy be analyzed, and what rating is likely required for the floor/ceiling assembly?
Read the worked answer
A change of occupancy is evaluated by comparing the required features of the new occupancy with what exists, using the code's change-of-occupancy provisions. The designer must determine the required fire separation between the R-2 and B occupancies, the required fire-resistance of the floor/ceiling assembly, and the required stair enclosure rating, then compare them to the existing construction. Group R-2 typically requires a 1-hour separation from other occupancies in this configuration, and the floor/ceiling assembly between stories often must be rated; an unrated wood-joist assembly with a single gypsum layer may not achieve 1 hour without a tested design.
The designer should document the existing assembly and, if it lacks the required rating, propose an upgrade such as adding a layer of Type X gypsum or a listed membrane to achieve a tested 1-hour assembly. The analysis must also address the open stair: an open stair between floors is generally not permitted where enclosure is required, so the first-floor opening must be enclosed or protected. The submittal should include a change-of-occupancy compliance table comparing required and existing features.
2. Evaluate the proposal to delete the sprinkler system. Is the occupant-load argument valid?
Read the worked answer
No. Sprinkler requirements are not driven by occupant load per square foot alone. For a change of occupancy to R-2, the code may require sprinklers based on the building's height, area, construction type, and the new occupancy, and the existing building may already rely on sprinklers to satisfy other provisions, such as the open stair, the floor/ceiling rating, or allowable area. Deleting the system could invalidate those allowances and force additional upgrades.
The designer must perform a full analysis: determine whether sprinklers are required for the R-2 occupancy independent of occupant load; identify every code allowance currently relying on sprinklers (open stair, travel distance, rating reductions); and calculate the cost and feasibility of the alternative upgrades if the system is removed. In most cases, retaining the sprinkler system is the lower-risk path. The building official should reject a deletion proposed solely on the basis of reduced occupant density and require a complete code analysis before any permit is issued.