Appeal 35083

2022 OSSC §707.5.1 Supporting Construction – Fire Barriers

RECONSIDERATION:
Section 707.5.1 requires the supporting construction for a fire barrier to not be less than the required fire-resistance-rating of assemblies being supported.

ORIGINAL:
Table 601 requires load-bearing exterior walls to be 2-hour fire-resistance rated for Type III-B Construction.
Section 704.10 requires load-bearing structural members on the outside of a building to be rated as required by Table 601 for exterior bearing walls.

RECONSIDERATION:
Request for supporting construction of the highlighted exterior load-bearing walls enclosing three rooms at the roof to be unrated (see updated Attachment A).

ORIGINAL:
Request for highlighted exterior load-bearing walls enclosing three rooms at the roof to be unrated and for columns of the roof pavilion to be unrated (see Attachment A); all other elements will be rated as required.

RECONSIDERATION:
The James Beard Public Marketplace will include an occupied roof with a rooftop bar serving an unenclosed pavilion. The proposed design is to provide the prescriptive fire-resistance ratings required of exterior walls per §704.1 and Table 601, with the exception of the structural members supporting exterior walls which enclose the Rooftop Bar (Room 311), the Mechanical Room (Room 301), and a small Storage Room.

As part of this reconsideration, the exterior walls enclosing the rooms will be 2-hour rated as prescribed by Table 601.

See the updated Attachment A for a description of how building elements will be rated at the roof.

In lieu of providing a fire-resistance rating on supporting construction of these select exterior walls, the Rooftop Bar, Mechanical Room, and Storage Room will be protected by smoke detectors which are tied to the fire alarm system.

ORIGINAL:
The James Beard Public Marketplace will include an occupied roof with a rooftop bar serving an unenclosed pavilion. The proposed design is to provide the prescriptive fire-resistance ratings required of building elements per Table 601 and §704.10, with the exception of the unrated pavilion columns and of unrated exterior walls which enclose the Rooftop Bar (Room 311), the Mechanical Room (Room 301), and a small Storage Room.

See Attachment A for a description of how building elements will be rated at the roof.

In lieu of providing a fire-resistance rating at these columns and select exterior walls, the Rooftop Bar, Mechanical Room, and Storage Room will be protected by smoke detectors which are tied to the fire alarm system.

RECONSIDERATION:
The original Appeal 35603 text below describes how the design meets the code intent for providing sufficient egress time prior to the vertical load-carrying collapse of a building due to fire exposure, meets prescriptive unrated allowances based on Fire Separation Distance, and increases protection with the addition of spot type smoke detectors in the three rooftop rooms.

The exterior walls of the three rooftop rooms do not meet the Chapter 2 definition of “load-bearing” when considering the structural dead load. Type III-B construction does not require a rating for non-load bearing exterior walls. It is only when considering the addition of snow load that they meet the definition of “load-bearing” and require a 2-hr rating.

The 2-hour rating will be provided at the exterior walls, as an additional level of protection for this reconsideration. We respectfully request that supporting construction of these walls be permitted to be unrated based on the equivalent level of protection described in this appeal.

ORIGINAL:
The occupied roof will include an open-air pavilion supported by columns, and an enclosed Rooftop Bar, Mechanical Room, and Storage Room. The three rooms have walls which are not otherwise required to be rated, except that they are exterior load-bearing exterior walls in Type III-B construction. The open-air pavilion columns are load-bearing structural members required to be rated as structural members outside of a wall.

CODE INTENT
The IBC Code and Commentary for Table 601 explains that the intent of the fire-resistance rating requirements for load-bearing walls is “to delay the vertical load-carrying collapse of a building due to fire exposure for a predetermined amount of time.”

The Rooftop Bar, Mechanical Room, and Storage Room are small enclosures, each being less than 400 square feet. These rooms would only be occupied by employees or building maintenance staff that would be familiar with the building layout and location of the two exits provided at the roof. The estimated evacuation time to egress the mechanical room, which has the longest travel distance, is less than 15 seconds*. Upon egressing either space, occupants have a choice of proceeding to two different exit stairways. Due to the limited occupancy and size of the rooms, egress from these spaces can occur well before the threat of a potential collapse of the structure due to fire exposure, without requiring a fire-resistance rating.

The Rooftop Pavilion is approximately 1,350 square feet, with a rated stair enclosure provided at opposite ends. Based on the longest travel distance from the center of the pavilion, occupants can reach a rated exit in less than 10 seconds* and begin queuing to enter the enclosure.

*Travel times calculated based on an average walking speed of 4.10 ft/s as referenced in SFPE 4th Edition; travel distance to exit the mechanical room and travel distance to reach an exit enclosure from the pavilion center are less than 50’. Travel distance to reach an exit enclosure from the center of the pavilion is less than 40’.

OTHER CODE REQUIREMENTS
The code also requires exterior wall ratings to consider the Fire Separation Distance to adjacent buildings and properties. The unrated walls are more than 30’ from the Fire Separation Distance line they face, and do not require a rating per Table 705.5.

The columns are part of the primary structural frame, which also does not require a rating per Table 601. It is only per §704.10 Item 2, which requires load-bearing structural members located outside of the building to be rated as required for exterior bearing walls, that a 2-hr rating is required for the columns.

ADDITIONAL PROTECTION
To provide additional protection for the exterior walls, spot type smoke detectors that are tied to the building fire alarm system will be installed inside the Rooftop Bar, Mechanical Room, and Storage Room. This exceeds the baseline code requirements for these rooms, providing quick detection and awareness if a fire originates from these rooms even when unoccupied.

The columns will be of non-combustible construction. The pavilion is unenclosed and open to atmosphere, preventing accumulation of any smoke and heat with unobstructed airflow to the exterior. The pavilion is also centered on the rooftop within rated wall elements on either side that protect against exposure to adjacent buildings.

CONCLUSION:
The proposed design provides equivalent or greater fire/life safety protection to the code intent for exterior wall and column rating requirements. Therefore, we respectfully request that the design be permitted to provide smoke detectors in the three rooms in lieu of rating the exterior walls and columns identified in Attachment A.