Appeal 33661

OSSC 1007.1.1

1007.1.1 Two Exits or Exit Access Doorways
Where two exits, exit access doorways, exit access stairways or ramps, or any combination thereof, are required from any portion of the exit access, they shall be placed a distance apart equal to not less than one-half of the length of the maximum overall diagonal dimension of the building or area to be served measured in a straight line between them. Interlocking or scissor stairways shall be counted as one exit stairway.
Exceptions:

1. Where interior exit stairways or ramps are interconnected by a 1-hour fire-resistance-rated corridor conforming to the requirements of Section 1020, the required exit separation shall be measured along the shortest direct line of travel within the corridor.
2. Where a building is equipped throughout with an automatic sprinkler system in accordance with Section 903.3.1.1 or 903.3.1.2, the separation distance shall be not less than one-third of the length of the maximum overall diagonal dimension of the area served.

Consideration of interlocking stairs with a 2-hr rated separation as two exit stairways.

Project is adaptive re-use of a 5-story, 25,000 gross square foot building built in 1893 with unreinforced masonry perimeter bearing walls and heavy timber beams and columns. The building is currently vacant and marked “U” by the Portland Fire Marshal. The existing building includes one fire egress stair with encroachments within required headroom. The building is not sprinklered and an exterior standpipe is the only means to provide fire suppression to upper levels and roof. The existing building has no openings on the north and west elevations, the shared property lines.

The proposed work on the building includes change of use to R-2 with 34 residential units on Levels 01 through 05 and limited B occupancy at the ground floor. The project will include a full ASCE 41 evaluation and upgrade; addition of an NFPA 13 sprinkler system; removal and reconstruction of the non-compliant stair; and addition of a second egress stair. Access to the two egress stairs will comply with the separation requirement of 1007.1.1.

The two egress stairs are proposed to be interlocking with a 2-hour separation between each stair and between the stair and the access to egress on each level as well as the access to exit at level 1.

This project aims to seismically-reinforce an existing Unreinforced Masonry Building, which requires careful consideration of the existing structure. The interlocking stairs will provide equivalent egress in a more compact footprint than two fully independent stairs. This will reduce the opening in the existing floor diaphragm, which in turn improves the seismic performance of the building.

The floor-to-floor heights of the existing building vary from 16’ 7” at level 1 to 14’ 8” at levels 2 – 4. The vertical rise of any stair flights between any two floors exceeds the maximum vertical rise allowed by OSSC 1011.8 for a single flight so intermediate landings will be required. The interlocking stair is the only configuration that allows for a single intermediate landing between each floor. Providing two noninterlocking stairs would result in each stair requiring three flights and two intermediate landings, with no reduction in exit separation distance. The greater number of turns and the unusual layout of these stairs would create a more confusing and less safe exit path for building users. The interlocking stair proposed is the easier and safer solution for occupants to navigate in case of an emergency.

Consideration of interlocking stairs with 2-hr separation as two separate stairs is supported by the 2021 IBC Code Commentary. It has also been approved via appeal by City of Portland for a 5-level, type III-B building with appeal 31597 and related appeals for each of the 13 buildings that are part of the NB30 Apartments project in NW Portland.

In recognition of the unique requirements of upgrading the existing structure (including floor-to-floor heights and diaphragm openings); the protection provided by the proposed fire separation walls and sprinklers; the increased safety afforded by the layout of the interlocking stairs; and previously granted appeals of similar nature, applicant requests that the appeal be granted.