Office-to-Apartment Conversion with a Single Stair
A 1974 six-story, 65 ft office building with 22,000 ft² per floor is being converted to apartments above a ground-floor restaurant and retail. The existing construction has a single 44 in. enclosed stair, no sprinklers, and a manual fire alarm with corridor smoke detection added in 1998. The owner's consultant says the building is a high-rise and therefore must be fully sprinklered and have a second stair. The project is in a jurisdiction that adopts the IBC with NFPA 101 as an alternative, and the building official has asked for a code analysis before accepting the permit set.
1. Determine whether the building is a high-rise under the IBC and NFPA 101, and explain the consequence for the design.
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Both the IBC and NFPA 101 use a 75 ft threshold, but not the same measurement. Under the IBC, a high-rise is a building with an occupied floor more than 75 ft above the lowest level of fire department vehicle access; under NFPA 101 the trigger is also a 75 ft height above the lowest level of fire department access. A 65 ft building does not become a high-rise merely because it has six stories.
The consultant's premise is therefore wrong unless the grade plane or fire department access is unusual. Confirm the elevation of the highest occupied floor, not the roof, and confirm the access level. If the occupied floor is below 75 ft, high-rise-specific requirements such as a fire command center, high-rise standpipe and sprinkler provisions, and voice evacuation are not triggered by height alone. The change of occupancy still triggers code requirements, but those must be analyzed separately rather than assumed from high-rise status.
2. The owner wants to keep the single stair. What code path and conditions must be satisfied?
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The conversion is a change of occupancy, so start with the adopted existing-building code's change-of-occupancy chapter and with the new-occupancy provisions of NFPA 101 for apartments. A single exit is not prohibited categorically, but the allowances are narrow: they are generally limited by story count, travel distance, occupant load per story, and full sprinkler protection, and they are not automatically available because the stair is enclosed.
A six-story apartment building is unlikely to qualify for a single exit under the prescriptive allowance. The practical paths are:
- Add a second means of egress; or
- Seek an equivalency or variance with a performance analysis showing the single stair, sprinklers, compartmentation, and smoke control provide equivalent safety; or
- Reduce the building height or separate the upper stories so the single-exit limits are met.
The ground-floor restaurant and retail must be separated from the residential occupancy and analyzed under their own occupancy chapters. Do not accept "the stair is existing" as a compliance argument.
3. What trade-offs and submittals would you recommend to the building official?
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Recommend a written code analysis that identifies the compliance method, the applicable editions, and each deficiency. The trade-off package should include:
- Full sprinkler protection throughout, with hydraulic calculations and water supply.
- A second stair or an equivalency analysis with fire modeling, egress modeling, and smoke control for the single-stair case.
- Upgrade of the existing stair enclosure, door assemblies, and signage to current requirements.
- Separation of the restaurant/retail from residential, including rated assemblies and independent egress.
- Fire alarm upgrade to apartment occupancy requirements, including in-unit notification.
- A phasing plan so occupied apartments are not left without protection during construction.
The submittal should state clearly which code path is being used and should not mix IBC and NFPA 101 requirements selectively. The building official is entitled to a single, coherent basis of design.