Building Code Guides (BCGs) and Building Official Determinations (BODs) provide answers about the application of building codes and outline optional alternates. BODs are typically smaller in scope and address simpler questions. Code Guides provide a comprehensive alternative to a complicated set of code requirements.
BCG 13-10: Type III Code Guide
QUESTION: In buildings of either Type III-A or III-B construction, the Oregon Structural Specialty Code (OSSC) permits fire-retardant-treated wood framing within exterior walls where the wall is 2-hour fire- resistance-rated or less.
May non-fire-retardant-treated wood be used as an alternative to fire-retardant-treated wood in these assemblies?
This question includes the condition in which the Special Provisions of OSSC Chapter 5 are utilized for a four or five-story, Type III building above a Type I-A podium building.
RESPONSE: Yes, in lieu of using fire-retardant-treated wood framing, theBureau of Development Services (BDS) will allownon-fire-retardant-treated wood framing within exterior walls of R-2 occupancy buildings of Type III construction without a building code appeal provided all of the conditions listed below are met.
DEFINITIONS AND TERMINOLOGY
Approved wall assembly: Wall assemblies designated “approved wall assembly” in the graphic details of this Guide must be constructed as described in the Conditions (below), unless it is a tested assembly.
Continuous and solid: The terms “continuous” and “solid” used in the details of this Guide means without air breaks or interruptions by a material of lesser fire rating for the full length and depth of the condition. A “continuous” or “solid” member may be built up of multiple wood members provided it complies with all structural requirements.
Sacrificial stud: The term “sacrificial stud” used in the graphic details of this Guide means an extra stud, 2-inch minimum nominal thickness and the same depth as the adjacent framing member, installed against a structural framing member to provide additional fire resistance at an opening in an exterior wall.
Tested assembly: A fire-resistant rated assembly that has been tested in accordance with the OSSC.
CONDITIONS
- Exterior bearing walls shall be protected based on their fire separationdistance as defined in the OSSC asfollows:
- Less than 10 feet: Protected on the inside with at least two layers of 5/8” minimum fire-rated gypsum board. Protected on the outside with at least two layers of fire-rated gypsum sheathing or one layer of fire-rated gypsum sheathing and one layer of 5/8” minimum fire-retardant-treated plywood. Alternatively, exterior bearing walls may be protected for fire exposure from both sides with a two-hour fire resistance testedassembly.
- Equal to or greater than 10 feet: Protected on the inside with at least two layers of 5/8” minimum fire-rated gypsum board. Protected on the outside with at least one layer of 5/8” minimum fire-rated gypsumsheathing.
- Exterior non-bearing walls shall be protected on the inside and outside with at least one layer of 5/8” minimum fire-rated gypsum board or gypsumsheathing.
- Non-fire-retardant-treated wood framing within exterior walls must beenclosed by gypsum board or gypsum sheathing, except where specifically noted in this Guide.
- All openings in exterior walls for doors, windows or wall-mounted HVAC units and louvers must be protected with a sacrificial studat the sides and top ofthe opening. The sacrificial studmay not be used to support a structural vertical load.
- All exterior wall coverings shall be of non-combustiblematerial.
- Combustible roof sheathing and framing shall be protected from exposure to fire from above with gypsum-based products, fire-retardant-treated wood sheathing or similar UL tested products installed above or below the roofing membrane and/or rigidinsulation.
- Selective smoke detection coverage shall be installed in the Type III portion of the building per NFPA 72, National Fire Alarm Code, beginning at theaccess point to the path of egress and continuing until reaching all exits. If the exit passes through a lobby or other intervening space, selective smoke detection coverage requirements shall be extended to such spaces until reaching the exit discharge.
- At least one operable exterior window shall be provided in each dwelling unit with a minimum opening width of 3-1/2inches.
- Walls and floor assemblies separating dwelling units shall have testedfire- resistance ratings of not less than1-hour.
- The base allowable building area specified in the OSSC for R occupanciesin Types III-A and III-B construction shall not exceed 12,000 square feet. Area increases in accordance with the OSSC areallowed.
- The distance from the top of the roof parapet to the lowest required fire apparatus setup point, as determined by the Fire Marshal’s Office, shall not exceed 75 feet. A minimum of one dominant street-facing building façade shall meet Fire Code requirements for fire apparatus aerialaccess.
- All required egress stairs shall include access to the roof. Such access may be via any method listed in OSSC Chapter 10 for roofaccess.
- All penetrations through the exterior wall covering shall be fire-stopped at the exterior sheathing. “Penetrations” for purposes of this Guide includes elements such as conduits and piping and does not include “openings” such as doors, windows or wall-mounted HVAC units andlouvers.
- Ducts and vents penetrating exterior walls shall be 26 gageminimum.
- No unprotected penetrations are permitted through the underside of fire-rated exterior wall projections that are required to be rated, including cornices, eaves, bays, exterior balconies, and similar projections extending beyond the exterior wall.
- Elevator hoistways opening directly into corridors shall be pressurized or have smoke-tight protection as required for doors opening into fire-resistivecorridors.
- Framing at walls, floors, ceilings and roofs must be constructed as specified in the graphic detail drawings numbered 0 - 19 contained in the PDF of the Guide below, unless greater fire resistance is provided. Conditions not covered in this Guide must be constructed in accordance with theOSSC.
HISTORY: Implemented May 13, 2013. Revised March 23, 2015, October 1, 2015, and March 30, 2023.
DOWNLOAD a copy of this Code Guide:
Download PDF fileOSSC Chapter 6: Non-Fire-Retardant-Treated Wood Framing Within Exterior Walls of R-2 Occupancy Buildings of Type III Construction 2.74 MB
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