Warehouse-to-Event-Venue Egress Analysis
A 1920s single-story brick warehouse measuring 100 ft by 150 ft with 18 ft clear height is being converted into an event venue: loose-table assembly for 600 guests, a 1,500 sq ft commercial kitchen, and a new 1,200 sq ft mezzanine office and control room 10 ft above the floor, served by one open stair. The building will be fully sprinklered with an emergency voice/alarm system. The two existing 36-in street doors are 90 ft apart on the same long wall; a third, 30-in door at the rear opens onto a fenced service yard that is not a public way. The design team proposes to retain all three doors and place the mezzanine stair at the center of the floor. The authority having jurisdiction has flagged the egress concept and asked for a code analysis before the next submittal.
1. Calculate the occupant load and required egress width. Do the existing doors work?
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Occupant load: the ground-floor assembly area is 15,000 sq ft minus the 1,500 sq ft kitchen, or 13,500 sq ft. At 15 net sq ft per person for tables and chairs, that is 900 occupants, not the 600 the client intends to seat. The kitchen at 200 gross adds 8, and the mezzanine office at 150 gross adds 8, for a total near 916. This gap between the marketing number and the code number is the first finding: either the layout must be constrained and posted at 600, or the exits must be sized for 900-plus.
Width: at 0.15 in per occupant for a sprinklered building with voice evacuation, 916 people require 137 in of clear width; at 0.2 in they require 183 in. The existing doors provide 36 plus 36 plus 30, or 102 in, and the 30-in rear door is below the 32-in clear minimum and discharges to a yard that is not a public way, so it cannot count. The doors fail on width, on count and on the discharge path. At least three exits are required for 501-1,000 occupants, so the scheme needs a new exit and a wider rear door before anything else is resolved.
2. Evaluate exit remoteness, travel distance and exit count.
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Diagonal: the square root of 100 squared plus 150 squared is about 180 ft, so the two exits must be separated by at least half that, or 90 ft. The two 36-in street doors are exactly 90 ft apart on the same wall, which is at the limit in a straight-line measurement and unreliable once travel paths are measured. More decisively, 916 occupants require three exits, and the rear door does not qualify because it opens to a fenced yard rather than a public way or an approved open area.
Travel distance: assembly occupancy, sprinklered, is limited to 250 ft. The 100 by 150 ft footprint probably keeps the far corner within that limit to a well-placed exit, but only if a third exit is added on the opposite long wall or a short wall, separated at least 90 ft from each existing door. Fixes: widen the rear door to 36 in and connect the yard to the public way, or delete it as an exit; add a new exit with panic hardware on the opposite side; and re-run the egress plan with the actual furniture layout and the 600-person posted load, not the 900-person calculated load.
3. Can a single open stair serve the mezzanine?
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Possibly, but only within narrow limits and with verification. A 1,200 sq ft mezzanine with 8 occupants is below the common 2,500 sq ft threshold for a single means of egress, and the travel distance from the furthest point to the stair is likely under 75 ft. Those are the conditions that allow one stair; confirm the exact thresholds with the adopted code and the AHJ, because the exception is specific and the assembly occupancy may add restrictions.
The open stair is a second issue. It must not discharge into the seating area in a way that obstructs egress, and its guards and handrails must meet the code. If the mezzanine is the only level served, an open exit access stairway is often permitted inside the allowed size, but an enclosed stair is safer and may be required by the AHJ. Accessibility is non-negotiable: the office and control room must be reachable by an elevator or platform lift, not the stair alone. Place the stair at the perimeter rather than the center so it does not divide the assembly floor or block sightlines, and show the mezzanine egress path on the drawings.