Warehouse Conversion With One Stair and No Sprinklers
A 1920s three-story, 27,000 sf unreinforced masonry warehouse is being converted. Floor 1 becomes mercantile (9,000 sf); floor 2 becomes an assembly space with tables and chairs (6,000 sf) plus 3,000 sf of business use; floor 3 remains business (9,000 sf). Construction is Type III-B. The building has one existing enclosed interior stair, 44 in. wide, serving all floors, and no automatic sprinkler system. The owner has $600,000 held for sprinklers and wants to know whether they are avoidable. The design team must resolve egress before the 60 percent submission, and the code official has agreed to review an alternate-means proposal.
1. Calculate occupant loads and evaluate the existing stair. Where does it fail, independent of sprinklers?
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Occupant loads using IBC Table 1004.5 (confirm the edition in force):
- Floor 1 mercantile, 60 gross: 9,000 / 60 = 150
- Floor 2 assembly, unconcentrated tables and chairs, 15 net: 6,000 / 15 = 400; business portion 3,000 / 100 = 30; floor total 430
- Floor 3 business, 100 gross: 9,000 / 100 = 90
Failures, before any sprinkler credit is considered:
- Number of exits. Floor 2 at 430 occupants, and every floor above 49, requires two means of egress. One stair cannot serve as both.
- Capacity. At 0.3 in. per occupant for stairways, the stair serving floors 2 and 3 must carry 430 + 90 = 520 occupants, or 156 in. of width. A 44 in. stair carries about 147 occupants. It is short by more than a factor of three.
- Discharge. If the stair discharges into the ground-floor mercantile space rather than to the exterior or a protected exit passageway, the exit is not continuous.
- Travel distance. Unsprinklered Group A-3 exit access travel is limited well below the sprinklered allowance; measure it before assuming the existing geometry works.
2. The owner asks whether the sprinkler money is avoidable. What does sprinklering actually buy here, and what does it not buy?
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Sprinklering buys real things, but none of them is a second stair.
What it buys:
- Reduced required capacity for level components and doorways (commonly 0.15 in. per occupant instead of 0.2). Stairway width generally stays at 0.3, so the 44 in. stair does not become adequate.
- Increased allowable travel distance for A-3, typically 250 ft versus 200 ft unsprinklered, which may rescue the floor 2 layout.
- Reduced fire-resistance and separation requirements, often the difference between a feasible and infeasible conversion in an unreinforced masonry shell.
- Compliance leverage with the existing building code, which typically rewards sprinklers with reduced upgrade obligations elsewhere.
What it does not buy: relief from the requirement for two means of egress for 430 assembly occupants. The second exit must be a real stair, an exterior stair, or a horizontal exit through a rated separation.
Also check the fire-area and occupant-load thresholds in IBC 903.2.1 against the edition and local amendments before promising the owner anything - sprinklers may be mandatory rather than optional.
3. Assume the owner will not add an interior stair. What alternate-means strategies would you put in front of the code official, and in what order of preference?
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Order them by cost, disruption, and how much of the problem each actually solves.
- Exterior steel stair at a rear or side elevation serving floors 2 and 3, discharging directly to grade. Lowest structural disruption to the shell, no lost leasable area, and it satisfies remoteness if placed at the opposite end from the existing stair. Best first option.
- Horizontal exit through a new 2-hour wall into an adjacent structure or an enclosed exit passageway, if the site has a viable adjoining building and the elevation works. Elegant but dependent on a neighbor's cooperation and a permanent easement.
- Reduce the assembly occupant load, which shrinks but rarely eliminates the problem. Even at 200 occupants, two exits are still required; this strategy only makes the second exit smaller and cheaper.
- Existing building code compliance alternative - a performance or work-area approach that trades sprinklers, a fire alarm, and rated corridors for reduced egress redundancy. Viable only if the analysis genuinely demonstrates equivalent safety, not as a bargaining tactic.
Bring the official a comparative matrix with egress capacity, travel distance, cost, and schedule for each. Do not lead with the alternative you know is weakest.