International Code Council Updated 93-Tall-Mass-Timber-Buildings Exam Questions and Answers by adriana

IBC Table 601 requires both exterior and interior bearing walls in Type IV-C construction to have a minimum two-hour fire-resistance rating. Option B is correct.

For exterior bearing walls, the Table 601 rating is not the only applicable criterion. Section 602.1 also requires exterior walls to satisfy Table 705.5 based on occupancy and fire separation distance. Where Table 705.5 or another provision imposes a more restrictive rating, the higher requirement governs.

The two-hour rating may be achieved through the calculated structural fire resistance of the mass timber, approved noncombustible protection, or an approved combination of the two. Connections, intersections, penetrations, and abutting edges must not create a premature failure path or compromise the rated assembly.

A one-hour reduction can be permitted for bearing walls supporting a roof only under Table 601, Footnote “a,” but that exception does not apply to a wall carrying floors or other qualifying structural loads. The inspector must confirm the actual load path before accepting any reduced protection at the uppermost level.

References/Topics: 2021 IBC Sections 601, 602.1 and 602.4; Tables 601 and 705.5; Type IV-C bearing walls.

The 2021 IBC definition of cross-laminated timber describes a prefabricated engineered wood product consisting of not less than three layers of solid-sawn lumber or structural composite lumber. The adjacent layers are cross oriented and bonded with structural adhesive to form a solid wood element. Accordingly, option C is correct.

Cross orientation means that the principal grain direction of one layer is arranged approximately perpendicular to that of the adjoining layer. This configuration distinguishes CLT from products in which all laminations run parallel, such as conventional glued-laminated timber. The cross-oriented layup provides two-way panel behavior, dimensional stability, and structural capacity in both principal directions.

Option A is incorrect because CLT must contain at least three layers. Option B describes a mechanically laminated product rather than structural glued CLT; nail-laminated timber uses mechanical fasteners, whereas code-compliant CLT uses structural adhesives and must conform to the applicable manufacturing standard. Option D eliminates the defining cross-lamination characteristic and would instead describe a parallel-laminated product.

During inspection, the product label and certification documentation should be checked to confirm the panel was manufactured under the required quality-assurance program.

References/Topics: 2021 IBC Chapter 2 definition of “Cross-Laminated Timber”; Sections 602.4 and 2303.1.4; ANSI/APA PRG 320.

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The illustrated configuration represents Type IV-C construction , so option C is correct. The distinguishing feature is the combination of noncombustible protection on the exterior face with an exposed CLT surface toward the interior.

IBC Section 602.4.3.1 requires the exterior side of combustible exterior walls in Type IV-C construction to have noncombustible protection providing a minimum assigned time of 40 minutes . Table 722.7.1(2) assigns exactly 40 minutes to one layer of 5/8-inch Type X gypsum board, matching the protection illustrated in Figure 66.

The decisive distinction is Section 602.4.3.2: mass timber elements in Type IV-C are permitted to be unprotected on the interior . This is fundamentally different from Type IV-A, where essentially all interior mass timber faces must be protected, and Type IV-B, where interior protection is generally required but limited areas may remain exposed under specific area and separation restrictions.

Type IV-HT does not use the Type IV-C protected-exterior/exposed-interior regulatory scheme.

References/Topics: 2021 IBC Sections 602.4.3, 602.4.3.1 and 602.4.3.2; Table 722.7.1(2), 5/8-inch Type X gypsum board = 40 minutes.

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Under the illustrated connection detail, the minimum wood-block dimensions are 3 inches by 3 inches. Therefore, option C is correct.

The block is part of the sacrificial wood-cover system used to protect the connection for the full two-hour fire-resistance period. It must provide sufficient timber beyond the protected connection region to account for calculated charring and the increased exposure that can develop at the interface between abutting wood members. Because the problem states that the CLT-to-glulam bearing area is already the minimum required, the primary members do not provide surplus material that can be credited as additional protection at that edge.

AWC connection-fire-design guidance requires the protective geometry to remain effective after the calculated char front advances. Char contraction can open a gap at abutting edges and expose material deeper in the connection than would occur on an uninterrupted planar surface. The 3-inch-by-3-inch block maintains the required protective envelope for the stated two-hour condition.

This dimension is specific to the illustrated configuration and assumptions; it is not a universal minimum for every mass timber connection. The inspector must verify the approved detail rather than substitute nominal blocking based solely on field availability.

References/Topics: AWC Technical Report 10; AWC Fire Design Specification provisions for wood-cover protection and char contraction at abutting members.

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