Appeal 32372

OSSC 703.2

2022 OSSC, Section 703.2 Fire resistance. The fire-resistance rating of building elements, components or assemblies shall be determined in accordance with Section 703.2.1 or 703.2.2 without the use of automatic sprinklers or any other fire suppression system being incorporated, or in accordance with Section 703.2.3.

703.2.1 Tested assemblies. A fire-resistance rating of building elements, components or assemblies shall be determined by the test procedures set forth in ASTM E119 or UL 263. The fire-resistance rating of penetrations and fire-resistant joint systems shall be determined in accordance with Sections 714 and 715, respectively.

703.2.2 Analytical methods. The fire resistance of building elements, components or assemblies established by an analytical method shall be by any of the methods listed in this section, based on the fire exposure and acceptance criteria specified in ASTM E119 or UL 263.

703.2.3 Approved alternate method. The fire resistance of building elements, components or assemblies not complying with Section 703.2.1 or 703.2.2 shall be permitted to be established by an alternative protection method in accordance with Section 104.10.

In order to comply with 2022 OSSC section 703.2.3 above, the following proposed alternate request is based on 2024 Fire Design Specification (2024 FDS) for Wood Construction by American Wood Council.

Per FDS Section 1.7.7 Protection of Connections
Where a wood member is required to have a fire-resistance rating, structural connections of that member shall be protected from fire exposure for the time corresponding to the required fire resistance rating of the wood member. Protection of the structural connection shall be established by test or designed in accordance with 3.10. Intersections of fire-resistance-rated assemblies shall be in accordance with 1.7.8.

Per FDS Section 3.10 Design of Protected Connections
Where a member or an assembly is required to have a fire-resistance rating, structural connections to that member or assembly shall be protected from fire exposure for the time corresponding to the required fire resistance rating of the member or assembly. All components of the structural connection, including connectors, fasteners and portions of the connected members that are part of the structural connection, shall be protected. Protection of the structural connection shall be provided by wood, Type X gypsum panel, other approved materials, or a combination thereof. Each wood cover layer shall be attached with fasteners of sufficient length to penetrate the adjacent member or cover at least one inch. Fasteners attaching the protection shall not be required to be protected; however, wood cover shall be attached in accordance with 3.4.1.4 and Type X gypsum panel protection shall be attached in accordance with 3.4.2.3.

Per FDS Section 3.4.2 Protection by Type X Gypsum Panel Products
Fire-rated gypsum panel products (Type X) shall be permitted as protection to increase fire resistance of wood members and assemblies.
3.4.2.1 Gypsum panel cover: Where used to increase fire resistance of wood members, the protection time, tp, provided by each layer of Type X gypsum panel cover that is in contact with either the protected member or another underlying layer of protection shall be as provided in Table 3.4.2.1.
3.4.2.2 Gypsum panel membrane: Where Type X gypsum panels are used as a membrane to protect the entire wood member or assembly, the protection time, tp, provided by each layer of Type X gypsum panels shall be in accordance with Table 3.4.2.1.
Table3.4.2.1 states 40 minutes of fire protection for 5/8” Type X gypsum board, with the following foot notes:
1 Each gypsum panel layer shall be attached with fasteners of sufficient length to penetrate the wood member at least 1 inch or be attached to steel channels capable of supporting the weight of the gypsum panel.
2 Where multiple layers of gypsum panels are required, all adjoining panel edges shall be offset at least 16 inches from those of the adjacent underlying layer and attached with fasteners offset at least 4 inches in both orthogonal directions from the fasteners in all underlying layers.
3 Gypsum panel cover attached to wood members shall be installed such that gypsum panel cover at outside corners overlaps by at least the thickness of the gypsum panel. For gypsum panel cover attached to horizontal wood members (e.g. wood beams), side layers are installed first, followed by the bottom layer(s) to ensure that the edges of the side layers are covered.
4 Panel edges of the gypsum panel membrane face layer shall be taped and finished with joint compound, and fastener heads shall be covered with joint compound.
5 Where multiple layers of gypsum panels are required, adjoining panel edges occurring over framing shall be staggered at least one framing spacing from those of the adjacent underlying layer and attached to framing with fasteners offset at least 4 inches from the fasteners in all underlying layers. Unbacked adjoining panel edges shall be offset by at least 12 inches from those of the adjacent underlying layer.

3.4.2.3 Fasteners attaching gypsum panel products: Each Type X gypsum panel layer shall be attached with fasteners of sufficient length to penetrate the wood member at least 1 inch or be attached to steel channels capable of supporting the weight of the gypsum panel. Fasteners attaching gypsum panel shall not be required to be protected.

Per FDS Section 3.6.2 Thermal Separation Time Provided by Type X Gypsum Panel Products
3.6.2.1 Gypsum panel cover or membranes: The contribution of Type X gypsum panel layers to the thermal separation time shall be equal to the sum of protection times assigned to each layer, determined in 3.4.2, except where a single layer of Type X gypsum panel is used to provide thermal separation or where the final layer on the unexposed side of the thermal separation is Type X gypsum panel, the time assigned to that Type X gypsum panel layer, determined in 3.4.2, shall be multiplied by 0.50.
3.6.2.2 Gypsum panel product contraction: Where Type X gypsum panel contraction will cause gaps to form between adjoining gypsum panels that are initially considered to be in contact, ignition of combustible materials directly behind the gaps shall be assumed to occur at the time assigned to that Type X gypsum panel layer, determined in 3.4.2, multiplied by 0.50; however, the effect on the thermal separation time, estimated in 3.6.2.1, shall be permitted to be ignored.

This project is located on 1.12 acres in the West Portland Town Center. The new fully affordable 5-story building will provide 96 units within an estimated 94,810 square feet. Construction type is four stories of Type VA over one story of Type IA. In the Type VA construction, the wood posts are connected to glulam wood beams with steel plates and connectors. The required 1-hour fire protection is provided by two layers of gypsum board, per Exhibit EX-1.
Per FDS Table 3.4.2.1 each layer of 5/8” Type X gypsum board provides 40 minutes of fire protection. Per section 3.6.2.1 the first layer of 5/8” gypsum board adjacent to the steel connection is multiplied by 0.5, providing 20-minute fire protection. Therefore, the total fire protection rating for two layers of 5/8” Type X gypsum board is 60 minutes, equaling that of wood post and beam fire rating.

The proposed two layers of 5/8” Type X gypsum board over the connections of the beam to post provides adequate 60-minute fire protection.