Appeal 24926

OSSC 703.2, OSSC 715.1

OSSC 703.2: Requires fire-resistant rating of building elements, components or assemblies shall be tested in accordance with ASTM E119 or UL 263

OSSC 715.1: requires fire resistant joint systems in specified locations where walls or walls and
floor-ceiling assemblies meet.

The proposed appeal seeks approval of an alternate method of design to satisfy required fire resistance for the exhibited CLT details.

The building is a 3-story mixed-use building of Type V-B construction incorporating cross-laminated timber (CLT) panels used as exterior wall assemblies and shaft enclosure assemblies. 1-HR fire resistance is required at exterior walls on the north and south sides of the building due to zero lot-line conditions. The east exterior wall requires a 1-HR fire resistance rating with unprotected openings due to fire separation distance. Within the building, 1-HR ratings are required at the elevator shaft, stair enclosure, and mechanical shafts. 5-ply CLT panels provide 1-HR fire resistance as tested per ASTM E119.

The design elements seeking appeal are vertical ‘half-lap’ joints connected the CLT wall panels and perpendicular ‘T-Joints’ where CLT wall assemblies meet. The original permitted drawings showed fire sealant at both of these locations, but due to the constraints of tilt-up construction the sealant was not installed. The appeal proposes to allow the joints to stay as constructed without the addition of fire sealant.

Per the attached exhibit by Code Unlimited, the omission of fire sealant in the as-built conditions does not adversely impact the fire resistance, structural integrity, durability, or safety of construction:

Tests conducted in accordance with ASTM E119 demonstrate that the half-lap joints do not permit the passage of heated gases for the duration of the test exposure. As such, OSSC §715.1, Exception 9 requires no additional protection of these joints to achieve the required fire resistance (see attached Exhibit, Section 3.1).

The perpendicular ‘T-Joint’ connection at the stairway and vertical shaft enclosures are connected in such a manner as to achieve a high degree of rigidity for seismic performance with no discernible gap through which smoke or heated gasses could pass. The natural charring characteristics of the CLT material along with the dead-air space of an interior corner would further inhibit flow through assembly conditions. The exceptions to OSSC §714.4.1 recognize situations that do not require protection using intumescent materials. Similar principles apply to joints between assemblies (see attached Exhibit, Section 3.2)

Furthermore, there is the opinion that intumescent materials are incompatible with CLT panels and can prove to be detrimental and are therefore generally inadvisable. As such, the approval of
these conditions in accordance with OSSC §104.11 is consistent with the intent of the code.