Pass the International Code Council Special Inspector 93-Tall-Mass-Timber-Buildings Questions and answers with CertsForce

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.

===============

The requirement applies to Type IV-C construction. Under the 2021 IBC provisions governing Type IV-C, combustible construction forming concealed spaces must be protected with noncombustible protection having an assigned protection time of not less than 40 minutes. Therefore, option C is correct.

The assigned protection time is determined using the protection-time values prescribed by the code, including the applicable values for gypsum board and other approved noncombustible materials. The provision is intended to delay ignition and involvement of combustible mass timber surfaces located within concealed spaces, where fire growth might otherwise remain undetected and become difficult for fire-suppression personnel to access.

Type IV-A and Type IV-B are subject to more extensive noncombustible protection requirements because those construction types support taller buildings and require greater protection of mass timber elements. Type IV-HT uses the traditional heavy-timber concealed-space provisions and may employ alternative methods, such as complete filling with noncombustible insulation.

During inspection, the special inspector must confirm that the installed layers, thicknesses, fastening patterns, joints, penetrations, and transitions collectively provide the required 40-minute assigned protection time.

References/Topics: 2021 IBC Section 602.4.3.5; Table 722.7.1(1); Type IV-C concealed-space protection.

===============

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.

===============

The 2 × 2 block is intended to protect the abutting wood edges from the effects of char contraction. Therefore, option D is correct.

During fire exposure, wood chars and the char layer can shrink or contract. At an interface between two abutting timber components, that contraction can create a gap that allows heat and flames to penetrate deeper than predicted for a continuous exposed surface. AWC connection-fire-design methodology therefore requires additional protection at susceptible joints and interfaces. The block shields the abutting edges and maintains the sacrificial wood-cover path around the protected connection.

Its primary function is not decorative, nor is it simply an air-sealing component. Although limiting airflow can be a secondary consequence of closing the interface, the design purpose addressed by the technical guidance is control of premature fire penetration caused by char contraction. The block also should not be interpreted independently as a generic one-hour protective membrane for the steel ledger; the connection’s total rating depends on the complete approved protection assembly.

The inspector should confirm the block’s dimensions, species or product designation, fastening, continuity, and tight installation before the connection is concealed.

References/Topics: AWC Technical Report 10; AWC Fire Design Specification provisions addressing char contraction and gaps between abutting wood members.

ANSI/APA PRG 320 is the governing product standard for performance-rated cross-laminated timber, including adhesive qualification, bond integrity, manufacturing quality control, and required product identification. Accordingly, option D is correct.

Bond-line performance is critical because CLT panels depend on structural adhesive to transfer shear forces between laminations and maintain composite action. PRG 320 establishes qualification and quality-assurance requirements intended to verify that adhesive bonds remain structurally reliable and resist delamination or inadequate bond development. Testing and manufacturing controls under this standard address the completed CLT product rather than treating the adhesive as an isolated material.

AITC 113 concerns dimensional tolerances and related requirements for structural glued-laminated timber rather than CLT bond-line shear qualification. ASTM C557 addresses adhesives for ceramic tile and is unrelated to structural timber manufacture. ANSI 117 is not the governing CLT manufacturing standard.

During inspection, the special inspector ordinarily does not reproduce factory bond-line tests on-site. Instead, the inspector verifies the CLT manufacturer’s identification, certification marks, panel grade, layup designation, and conformance with PRG 320 and the approved construction documents.

References/Topics: 2021 IBC Section 2303.1.4; ANSI/APA PRG 320; CLT adhesive-bond qualification and manufacturing quality assurance.

===============

The intended answer is ANSI/AWC NDS Chapter 16. The video option uses “AWS,” but the correct standards organization is the American Wood Council—AWC . Option D is therefore correct based on its intended reference.

IBC Section 722.1 expressly permits exposed wood members and wood decking to have their calculated fire resistance determined in accordance with Chapter 16 of the ANSI/AWC National Design Specification for Wood Construction. The method evaluates charring, the effective char depth, the reduced residual cross section, elevated-temperature effects, loading, and the remaining structural capacity for the required exposure period.

ACI 216.1 applies to concrete and masonry fire resistance. TMS 0216 addresses masonry assemblies. ASCE 29 Chapter 5 provides procedures for calculating the fire resistance of structural steel assemblies. Those references are code-recognized methods, but they apply to different construction materials.

For mass timber inspection, the approved calculations should identify the exposed surfaces, required rating, timber species or product, member dimensions, design loads, protective contribution, and connection treatment. Field reductions in member dimensions can invalidate the calculated fire resistance.

References/Topics: 2021 IBC Section 722.1; ANSI/AWC NDS Chapter 16; calculated fire resistance of exposed wood members and decking.

===============

Option A is the false statement. Under 2021 IBC Table 1705.5.3, bolted connections require periodic special inspection, not continuous special inspection.

The remaining three statements correspond directly to items contained in the table. Concealed connections are subject to periodic inspection. Erection of mass timber construction is also periodically inspected. For threaded fasteners, the inspector must periodically verify the use of pre-drilled holes where the approved design or manufacturer’s installation requirements call for them.

The distinction between periodic and continuous inspection is fundamental. Periodic inspection means the special inspector observes the work at appropriate intervals sufficient to verify compliance. Continuous inspection requires the inspector to be present continuously during the performance of the regulated work. Table 1705.5.3 reserves continuous inspection for the particularly installation-sensitive condition involving adhesive anchors installed horizontally or upwardly inclined to resist sustained tension loads.

For bolted connections, periodic inspection remains technically substantive. The inspector should verify bolt size and type, hole preparation, connection geometry, washers and nuts, required tightening, member condition, edge and end distances, and conformity with the approved structural drawings.

References/Topics: 2021 IBC Section 1705.5.3; Table 1705.5.3, Required Special Inspections of Mass Timber Construction.

===============

The fire resistance of a protected mass timber element is determined by adding the inherent fire resistance of the mass timber to the protection time contributed by the approved noncombustible protection. Therefore, option D is correct.

The mass timber component provides structural endurance through its large cross section and predictable charring behavior. The noncombustible protection delays heating, ignition, and charring of the protected timber surfaces. Its contribution may be established by testing or by assigned values permitted under IBC Section 722.7. The combined value must equal or exceed the rating required for the building element.

Option A ignores the additional protection contribution. Option B ignores the structural endurance provided by the timber after the protective membrane has performed its assigned function. Option C incorrectly substitutes “finish rating time.” A finish rating measures temperature rise behind a protective membrane and is not automatically the same as the added fire-resistance contribution established for protected mass timber.

Inspection must confirm that the protection system matches the approved calculation or tested configuration, including material type, thickness, layer count, fastening, edge treatment, joints, penetrations, and continuity.

References/Topics: 2021 IBC Sections 703.6, 703.8 and 722.7; protected mass timber performance method and noncombustible protection contribution.

Type IV-C generally permits interior mass timber surfaces to remain exposed, but shaft and elevator hoistway enclosures are a specific exception to that broad exposure allowance. Section 602.4.3.6 requires shafts, elevator hoistways, and interior exit stairway enclosures constructed with mass timber to receive noncombustible protection having a minimum assigned protection time of 40 minutes . Option A is therefore correct.

Critically, protection is required on both the inside and outside of the shaft enclosure . The 40-minute value is an assigned contribution from the noncombustible protection; the complete enclosure must still satisfy whatever overall fire-resistance rating is required by Sections 713, 713.4, Table 601, or other applicable provisions.

Option B incorrectly applies the general Type IV-C exposed-interior allowance to a specifically regulated shaft condition. Option C is incomplete because 1/2-inch Type X gypsum board provides only 25 minutes under Table 722.7.1(2), not the required 40 minutes. A 5/8-inch Type X board provides a recognized 40-minute contribution when installed in accordance with Section 722.7.2. Option D does not state the prescribed Type IV-C shaft requirement.

References/Topics: 2021 IBC Sections 602.4.3.2 and 602.4.3.6; Tables 722.7.1(1) and 722.7.1(2).

===============

The required minimum rating is two hours. Under 2021 IBC Table 601, the primary structural frame in Type IV-C construction must provide a two-hour fire-resistance rating. A structural connection joining members of that frame cannot be permitted to fail before the members it connects; consequently, the connection must remain functional for the same required period.

The protection requirement applies to the complete connection assembly. This includes steel plates, hangers, bolts, screws, dowels, fasteners, welds, bearing regions, and portions of the connected timber that form part of the connection. Compliance can be achieved through tested construction, calculated wood cover, Type X gypsum protection, another approved noncombustible system, or a combination documented by the registered design professional.

Option A is insufficient because it would leave a one-hour weakness in a two-hour structural load path. Option B similarly falls short of the required Table 601 rating. Option D is the Type IV-A primary-frame rating and is not required for the stated Type IV-C condition.

The special inspector must verify protective-cover dimensions and installation before connection hardware becomes concealed, including any project-specific inspection required for calculated wood-cover protection.

References/Topics: 2021 IBC Table 601 and Section 2304.10.1; AWC Fire Design Specification, protection of structural connections.

===============