Appeal 16266

712.1.8 Item 7

712.1.8 Two-story openings. In other than Groups I-2 and I-3, a floor opening that is not used as one of the applications listed in this section shall be permitted if it complies with all of the items below: …

1. Is separated from floor openings and air transfer openings serving other floors by construction conforming to required shaft enclosures.

Block 76W is a new 5-story mixed use building of approximately 23,000 sf. Occupancy will include Group B, M, and S. The building will be fully sprinklered Type IIIA construction utilizing CLT.

Block 76W includes a main 3-story lobby which will be separated into two 2-story spaces. The proposed design is for separation to be provided by a glass wall washed with WS type sprinkler heads 4” – 12” from glass and spaced 6’ O.C. to wash the entire surface of the glass in compliance with ESR-2397. See illustrations in Attachment 1.

The Block 76W building will be located in a prominent location at the east side of the Burnside Bridge. The building is planned for an unusually shaped, sloping parcel of land just west of Couch Street’s southward curve toward the Burnside Bridge.

The design for Block 76 West includes a central circulation space formed by two interlocking lobbies that visually connect 3 floors. Each of the lobbies includes a two-story opening, which overlap on Level Two. To separate the two-story openings from each other, a glass wall will form a fire barrier between the upper portion of the Level One lobby and the lower portion of the Level Two lobby.

The intent of Section 712.1.8 Item 7 is to reduce the risk of smoke migration or fire spread between multiple levels of a building. We propose to rate the glass wall between the Level One lobby and the Level Two lobby to 2 hours through the installation of Tyco Model WS Window Sprinklers. These sprinklers are UL Listed and are recognized by the ESR-2397 as providing a two-hour equivalency for a fire separation assembly (See Attachment 2). They have been tested per ASTM E119 and can protect heat strengthened, tempered, or ceramic glass windows for two hours without damage, including when a hose stream is applied to the glass. The sprinklers will be installed per the manufacturer’s instruction on both sides of the glass and will fully wash the glass from both sides when the sprinkler system is triggered. There will be no horizontal mullions that restrict the flow of water to the glass.

The Level One lobby is separated from the adjacent floor areas by a 1-hr fire barrier and is separated from the Level Two lobby by a 2-hr floor assembly. Due to the dramatic grade change on the site, each lobby includes egress directly to the exterior of the building at grade. The lobbies are small, and represent a low fuel load and low fire or life safety risk to occupants.

Given the successful testing of the Model WS Window Sprinklers, the extensive separation of the lobby areas, and the inherent low risk to occupants provided by the design, we believe the proposed design meets or exceeds the intent of the code to prevent fire spread and smoke accumulation.

1027.4, Egress Court

Egress courts serving as a portion of the exit discharge in the means of egress system shall comply with the requirements of Section 1027.

Stair B cannot terminate at the exterior face of the building due to encroachment into the public right-of-way. Per OSSC Section 1022.3, the designers have chosen to terminate Stair B at an egress court conforming to Section 1027.4:
--The egress court will be 5 feet deep by 12 feet wide and unobstructed to a height of 11 feet for the full width.
--There will be no reduction in width along the path of travel.
--Egress court will provide direct access to the public way.
--The capacity of the egress court will be greater than the aggregate capacity of the exits being served.

Additional protection will be provided in the form of sprinklers:
--Sprinklers will be provided at the interior of windows surrounding the egress court as shown in Attachment 3. Sprinklers will be between 4 and 12 inches from the glass. The sprinklers will be installed to wet the entire surface of the glass upon activation. There will be no horizontal mullions to restrict the flow of water.
--1 sidewall sprinkler will be provided where the floor above projects horizontally above the egress court.

Since exit doors cannot open into the public right-of-way, the door leading from Stair B has been recessed from the exterior face of the building to create an egress court. The egress court will not be directly open to the sky above but will be limited in area to 5 feet deep by 12 feet wide and will be completely open on one side. The degree of openness will insure that smoke and toxic gasses will not accumulate and will vent upwards and away from people evacuating the building.

The walls of the egress court are not required to be rated since the court is more than 10 feet wide, however additional protection will be provided by sprinklers on the interior of the glass and a sprinkler above the egress court.

A code precedent has been set by atrium enclosure provisions that allow sprinklers on glass in lieu of a 1-hour fire barrier. The sprinklers on glass will wet the entire surface of the glass upon activation and are intended to protect the glazing material from breakage as a result of thermal shock. In the case of a fire event adjacent to the egress court, the sprinklers on glass will ensure a safe and protected path of egress travel for occupants. The sidewall sprinkler above the egress court will control any fire that starts in or spreads to the egress court.

We believe that the egress court, open to the exterior and protected with sprinklers on glass and a dry sidewall sprinkler, provides a level of safety at least equivalent to the code requirements. Therefore we ask that you grant the proposed exiting arrangement from Stair B.

704.10 Exterior structural members. 711.4 Continuity

704.10 Exterior structural members. Load-bearing structural members located within the exterior walls or on the outside of a building or structure shall be provided with the highest fire-resistance rating as determined in accordance with the following:

1. As required by Table 601 for the type of building element based on the type of construction of the building;
2. As required by Table 601 for exterior bearing walls based on the type of construction; and
3. As required by Table 602 for exterior walls based on the fire separation distance.

711.4 Continuity. Assemblies shall be continuous without openings, penetrations or joints except as permitted by this section and Sections 712.1, 714.4, 715, 1009.3 and 1022.1. Skylights and other penetrations through a fire-resistance-rated roof deck or slab are permitted to be unprotected, provided that the structural integrity of the fire-resistance-rated roof assembly is maintained. Unprotected skylights shall not be permitted in roof assemblies required to be fire-resistance rated in accordance with Section 705.8.6. The supporting construction shall be protected to afford the required fire-resistance rating of the horizontal assembly supported.

Block 76W has specific locations where a glulam beam and/or column is required to be 2-hour rated. See Attachment 4, Figure 1 for the locations of the columns and Attachment 5, Figure 1 for the location of the beams. The glulam members have been sized for 1-hour fire resistance per char rate calculations in accordance with Chapter 16 of ANSI/AF&PA National Design Specification for Wood Construction as permitted by the 2015 IBC. Glulam columns required to be 2-hour rated will be individually encased with a double layer of 5/8” Type X gypsum board. Glulam beams required to be 2-hour rated will be provided with a double layer of 5/8” Type X gypsum board on the exposed surfaces.

The proposed 2-hour rated columns and beams are not a listed assembly. Therefore engineering analyses provide supporting data for the 2-hour rating of the columns and beams, respectively. See Attachment 4 for an analysis of the proposed columns and Attachment 5 for the beams.

The columns are required to be 2-hour rated in 2 locations: 1) exterior structural members are required to be 2-hour fire-resistance-rated in Type IIIA construction and 2) supporting columns for the 2-hour Lobby 2 floor assembly must provide the same 2-hour rating as the assembly they are supporting.

The beams supporting the 2-hour rated Lobby 2 floor must also provide the same 2-hour rating as the assembly they are supporting.

The attached engineering judgments conclude that the additive resistance of the 1-hour glulam member design plus 2 layers of 5/8” gypsum board will provide the required 2-hour fire-rating. We ask that you approve this proposed design.