Corridor Clear Width After Finish Build-Up
A tenant fit-out is proposed on the third floor of an existing six-story, fully sprinklered office building. The new corridor runs 48 ft between the elevator core and a demising wall and serves 58 occupants in the new suite plus 22 occupants in an adjacent suite that shares the corridor. The architect shows 5 ft 2 in. clear between the face of the new demising partition and the face of the core wall. The demising partition is 5/8 in. Type X gypsum board on 3-5/8 in. steel studs. The core wall will receive 5/8 in. gypsum board furring, and both corridor walls will receive a 3/4 in. wood base. A 10 in. deep display niche is recessed into the demising wall between 30 in. and 72 in. above finished floor. The suite entry door is 36 in. wide and swings into the corridor. The contractor has not yet installed the furring or base and asks whether the corridor will comply as drawn, and whether the niche and door swing can remain. The building has a 7 in. riser and 11 in. tread stair.
1. Determine the minimum required corridor width and the clear width that will remain after the furring and base are installed. State whether the corridor complies, showing each deduction.
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Step 1 - Occupant load and capacity. The shared corridor serves 58 + 22 = 80 occupants. In a sprinklered building, corridor egress capacity is 0.2 in. per occupant (IBC 1005.3.1): 80 × 0.2 = 16 in. Capacity does not govern.
Step 2 - Minimum width. IBC 1020.2 requires a 44 in. corridor where the occupant load is 50 or more; the 36 in. reduction applies only below 50 occupants. Required width = 44 in.
Step 3 - Finish deductions. Start with the 62 in. clear shown. Subtract 5/8 in. furring on the core side and 3/4 in. base on each side: 62 − 0.625 − 1.5 = 59.875 in. clear.
Step 4 - Niche and door swing. Because the niche is recessed, it does not reduce clear width. If it projected 10 in., the remaining width would be 49.875 in., still above 44 in., but projections must be checked at all heights and for the accessible route. A door swinging into the corridor may not reduce the required egress width below one-half of the required width; verify the open leaf does not create a pinch point.
Conclusion: the corridor remains above the 44 in. minimum, but compliance depends on field measurement of finished faces, not the architect's nominal dimension.
2. The inspector measures 62 1/2 in. between stud faces before gypsum board is installed. Does that change the conclusion? What must be verified before close-in?
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The stud measurement is not the code measurement. Clear width is measured between finished surfaces at the narrowest point, including gypsum board, furring, base, trim, door frames, and any projections.
Using the stud faces: subtract 5/8 in. board on the demising side, 5/8 in. board plus 5/8 in. furring on the core side, and 3/4 in. base on both sides: 62.5 − 0.625 − 1.25 − 1.5 = 59.125 in. This still exceeds 44 in., so the conclusion does not change. Before close-in, verify:
- the 44 in. clear width is maintained at door frames, the niche, and base locations, not just at mid-corridor;
- the door swing does not reduce the required width below half;
- the accessible route maintains 36 in. clear and required turning space;
- the partition assembly, including the recessed niche, matches the approved fire-resistance and finish details.
A single average measurement is not sufficient; the inspector should check the narrowest point.
3. The owner proposes adding 15 in. of built-in millwork along the core wall to create display shelving, leaving exactly 44 in. clear at the narrowest point. Evaluate the proposal.
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Exactly 44 in. is the minimum required width for this corridor because the shared occupant load is 80, so the proposal is theoretically at the limit. In practice, it is difficult to defend: construction tolerances, base, trim, shelf projections, and door swings can reduce the clear width below 44 in. at localized points. The built-ins also narrow the accessible route, which needs 36 in. minimum but still must be part of a compliant route with adequate turning and door clearances.
The proposal should not be approved on a nominal 44 in. dimension alone. Require dimensioned shop drawings showing the narrowest finished clear width, including base and trim; verify the door swing does not reduce required width below half; and require field measurement before fabrication. If any point measures below 44 in., the millwork must be reduced or omitted. A better design keeps a margin above the minimum rather than building exactly to it.