Appeal 34950

OSSC 3102.1

3102.1 General. The provisions of Sections 3102.1 through 3102.17 shall apply to air-supported, air-inflated, membrane-covered cable, and membrane-covered frame structures, collectively known as membrane structures, erected for a period of 180 days or longer. Those erected for a shorter period of time shall comply with the International Fire Code. Membrane structures covering water storage facilities, water clarifiers, water treatment plants, sewage treatment plants, greenhouses and similar facilities not used for human occupancy are required to meet only the requirements of Sections 3102.3.1 and 3102.7. Membrane structures erected on a building, balcony, deck or structure for any period of time shall comply with this section.

We are requesting permission to install two tents on the roof deck of the renovated Washington High School Building, without meeting the construction type and story requirements of the 2022 OSSC.

The proposed design is a revision/update to the tent design of the previously approved Appeal 12667. The 1,600 sf tent is being replaced with a new 800sf steel framed structure; the 280sf tent is unchanged from the previous design. This appeal also updates the roof deck per the recently completed building permit 24-062286-FA. Both tent structures will comply with the requirements of Section 3102 Membrane Structures and will be provided with the following additional safety measures to address any concerns.

LIMITED USE AND MONITORING:
• Both tents will be installed in May and taken down by the end of October each year, limiting the use to no more than 180 days.
• The tent on the east side of the deck shall be limited (reduced) to 800sf and the tent at the west side shall be unchanged and limited to 280sf., as shown in the attached exhibit. Access to the west tent shall be limited to employees only. Approximately half of the east tent will be limited to employee use.
• Staff hired by the owner/operator shall be trained to monitor the activities and provide assistance in case of an emergency.

STRUCTURAL DESIGN
• The modified tent will be an engineered design, meeting the requirements of OSSC 2022 Table 1607.1 including 100psf uniform loads (assembly areas) and will be seismically anchored to the deck structure.
• The building roof and deck will support the additional structural load induced by the new tents.

LIMITED FUEL LOADS
• The structural frame of both tents will be of non-combustible construction.
• The tents roof membrane will be self-extinguishing type complying with NFPA 701 standard.
• The furniture under the tents will have non-combustible frames with seats/backs having flame spread of 75 or less and smoke spread of 450 or less.
• There will be no cooking or food warming on the roof deck.
• No open flame devices will be permitted on the roof deck.
• Smoking will not be permitted on the roof deck and approved “No Smoking” signs will be conspicuously posted in addition to staff monitoring enforcement.

FIRE PROTECTION
• Fire extinguishers 4A:80B:C or better will be provided within 50 feet travel distance from any point under both tents.
• Two standpipe connections will be provided at the roof deck level. One will be provided in the main (east) exit stair and one will be provided at the exterior of the westside elevator vestibule. A hose reel shall be installed at the roof level with adequate length to reach all areas of both tent structures with a 30 ft hose stream.

MEANS OF EGRESS
• Access to two exits with adequate width to accommodate 150% of the calculated occupant load.
• Readily visible exit signage and emergency illumination will be provided above the doors leading from the roof to the exist stairs.
• Audio and visual notification devices connected to the building fire alarm will be provided at the two exit access doors from the roof.
• The egress path connecting the covered assembly area and the building access will remain open to the sky.
• The tents will remain open on all sides; no side panels that may restrict free movement will be installed.

The City of Portland has determined that tent structures on the roofs of buildings shall be designed as permanent structures, even if they were installed on temporary or seasonal basis. The IBC commentary clarifies the reasons behind that approach. Many of the additional safety measures proposed in the 2015 appeal were deemed adequately rigorous to have been adopted as state amendments in subsequent updates to the Oregon Structural Safety Code (OSSC). This proposal reduces the total area of roof deck with a tent cover by more than 40% as compared to the previously approved Appeal 12667. We believe the proposed additional safety measures, operational plans, and net reduction in tent area address any concerns.

The concerns addressed in the IBC commentary are as follows:

1. Means of Egress: This is addressed in our proposal by providing two means of egress from the roof deck. Each exit has adequate egress width to accommodate 80% of the total roof deck occupant load (door width is limiting; stair width accommodates 90% of load). The presence of the tents will also reduce the occupant load due to the space occupied by the tent structure and the support/service functions under 780sf of the 1,080sf of tent area. Illuminated exit signs and audiovisual notification devices are provided to ensure prompt evacuation in case of an emergency.
2. Limitation of Hazardous Materials: The tent will not be used for any storage of fireworks or other hazardous materials. Cooking and warming of food will not occur at the roof deck. The furniture under the tents will be made of non-combustible framing with seat backs made of materials having FSI of 75 or less and SDI of 450 or less.
3. Structural Design of the Tent Structures: A registered Oregon Structural Engineer has verified that both tent designs meet or exceed the requirements of permanent structures.
4. Additional Loads Imposed by the Tent Structure on the Structure Below: A registered Oregon Structural Engineer has verified that the building/deck structure is capable of handling the additional load induced by the tent structure, meeting OSSC Table 1607.1 requirements for 100psf uniform loads.

The following additional measures provide protection beyond the concerns raised by the IBC commentary.
• This proposal requires that the roof deck tenant/operator meet with a representative of the building owner each year following the installation of the tents to review the requirements of this appeal and the staff training and at the end of each season to ensure that the tents have been removed. This reduces the probability of accidents due to unrestricted use.
• Fire protection measures such as having fire extinguishers, access to standpipes, and access to a hose reel will provide enhanced protection beyond that envisioned by the code.
• The building below is of Type II-A construction which ensures that the tent is separated from the building below by a 1-hour rated assembly.
• The building below is of Type II-A construction which ensures that the structural frame of the building below is non-combustible construction.
• The tent areas will be limited to 800sf and 280sf – less than the 1/3 of the total roof deck area.
• The tent fabric will be self-extinguishing type, which means that in case it catches on fire it will only result in a hole in the roof but will not extend any further. Such a hole will allow the venting of smoke and hot gases and protect the occupants as they exit the area.
• No side panels will be installed on the tents in order to ensure full exit access.
• Both tents are open on all four sides. In the event that a fire were to begin under one of the tents, smoke and hazardous gases would be allowed to escape around all four sides before building up and pushing down to the occupant zone.

We believe that the safety measures and other precautions stated above provide users with protection beyond those anticipated by the code. Therefore, we urge you to approve this proposal.