Appeal 24938

602.3, Table 601, 704.1, 2303.2

OSSC Section 602.3 – Type III: … Fire-retardant-treated (FRT) wood framing complying with Section 2303.2 shall be permitted within exterior wall assemblies of a 2-hr rating or less.

OSSC Section 2303.2 Fire-Retardant-Treated Wood: FRT wood is any wood product which, when impregnated with chemicals by a pressure process or other means during manufacture, shall have, when tested in accordance with ASTME E84 or UL 723, a listed flame spread index of 25 or less and show no evidence of significant progressive combustion when the test is continued for an additional 20 minutes. Additionally, the flame shall not progress more than 10 ½ feet beyond the centerline of the burners at any time during the test.

In lieu of pressure-impregnated FRT glulams, bearing wall glulams supporting the exterior wall assembly will provide protection through a calculated char layer. Please see attached structural calculations.

This project consists of Type III-B construction using FRT wood framing at the exterior walls (over two levels of I-A). In a few locations glulam beams are used within the 2-hr exterior wall assembly to span larger window and door openings. Please reference included framing plans for highlighted locations.

In lieu of pressure-impregnated FRT glulams, bearing wall glulams supporting the exterior wall assembly will be shop treated with a tested, fire retardant treatment, Flame Stop IM and/or field applied with this product or Lumber Guard LX product will be applied in field as needed. This provides equivalent protection as pressure-impregnated FRT lumber. See the attached field- applied fire retardant coating product test report, the same product proposed for a similar appeal 12610 and 14674, which were approved for field application to protect the glulam beams on all sides in a similar Type IIIB construction project.

The glulam beams are discrete elements in our building envelope, independent of large portions of wall framing. The beam is protected by (2) layers of Type “X” gypsum to the interior and FRT sheathing to the exterior. The beams are directly below sheathing, thus preventing heat-rise air flow that would induce flame spread. The glulam beams in this project are located within the rated exterior wall assembly. Finally, glulam beam sizes exceed the minimum section sizes required to be classified as a heavy timber element and thus maintain an internal temperature during a fire event. This allows the element to char at a predictable rate rather than rapidly combust like traditional light-frame construction. The structural engineers have sized the members to account for the char rating necessary to achieve the hourly rating and continue to be structural viable for the duration of the fire event. Even so, we propose to coat all faces of the beam prior to installation of the sheathing or gypsum.

RECONSIDERATION TEXT:

This project consists of Type III-B construction using FRT wood framing at the exterior walls (over two levels of I-A). In a few locations glulam beams are used within the 2-hr exterior wall assembly to span larger window and door openings. Please reference included framing plans for highlighted locations.

In lieu of pressure-impregnated FRT glulams, bearing wall glulams supporting the exterior wall assembly will be sized to char and maintain structural integrity in a fire event. See attached calculations.

The glulam beams are discrete elements in our building envelope, independent of large portions of wall framing. The beam is protected by (2) layers of Type “X” gypsum to the interior and FRT sheathing to the exterior. The beams are directly below sheathing, thus preventing heat-rise air flow that would induce flame spread. The glulam beams in this project are located within the rated exterior wall assembly. Finally, glulam beam sizes exceed the minimum section sizes required to be classified as a heavy timber element and thus maintain an internal temperature during a fire event. This allows the element to char at a predictable rate rather than rapidly combust like traditional light-frame construction. The structural engineers have sized the members to account for the char rating necessary to achieve the hourly rating and continue to be structural viable for the duration of the fire event.

Type IIIB construction allows glulam beams, but as part of the exterior wall system, they must be fire-retardant treated. In our findings, pressure-impregnated FRT glulam beams from a majority of glulam manufacturer’s are not warrantable due to the FRT chemicals altering the structural integrity of the glulam beams. In order to use pressure-impregnated FRT beams, a structural reduction factor must be utilized and the beams become significantly oversized. Additionally, the FRT chemicals are corrosive to the metal fasteners attaching to the beams. A non-toxic, non-corrosive alternative offers an equivalent fire protection of the beams and will not reduce the structural integrity of the glulam beams.

RECONSIDERATION TEXT:

Type IIIB construction allows glulam beams, but as part of the exterior wall system, they must be fire-retardant treated. In our findings, pressure-impregnated FRT glulam beams from a majority of glulam manufacturer’s are not warrantable due to the FRT chemicals altering the structural integrity of the glulam beams. In order to use pressure-impregnated FRT beams, a structural reduction factor must be utilized and the beams become significantly oversized. Additionally, the FRT chemicals are corrosive to the metal fasteners attaching to the beams. Char happens at a predictable rate and can provide sufficient protection in this instance.