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

IBC Section 722.7 establishes the governing calculation principle for protected mass timber. The required fire resistance consists of the inherent fire resistance of the unprotected mass timber element plus the protection time contributed by the noncombustible protection . Therefore, option D is correct.

This approach recognizes two sequential protective mechanisms. First, the noncombustible covering delays heating and charring of the timber. After the credited protection period, the remaining mass timber cross section provides structural fire resistance through predictable charring behavior and residual section capacity. Section 722.7.1 further requires the contribution of the covering material to comply with the prescribed protection times or to be established under Section 703.6.

Option A ignores the contribution of the protective membrane. Option B ignores the inherent structural fire resistance of the timber. Option C incorrectly substitutes a finish rating for the code-recognized protection contribution. A finish rating is a separate temperature-based performance concept and is not automatically additive as the protection time used by Section 722.7.

References/Topics: 2021 IBC Sections 602.4, 703.6, 722.7 and 722.7.1; calculation of protected mass timber fire resistance.

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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.

The applicable standard is ASTM E119 , making option B correct. IBC Section 703.6 establishes a performance method for determining the number of minutes contributed by noncombustible protection applied to mass timber.

The methodology requires two otherwise identical assemblies to be evaluated using the procedures of ASTM E119 or UL 263 . Test Assembly 1 is tested without the protective covering. Test Assembly 2 incorporates the representative noncombustible protection, including its actual configuration, attachment details, joint treatment, accessories, and other relevant installation conditions. The protection contribution is then calculated by subtracting the fire-resistance time of the unprotected assembly from that of the protected assembly.

ASTM E119 is specifically designed to evaluate fire endurance of building construction and structural assemblies under standardized fire exposure. ASTM D3498, by contrast, is an adhesive specification referenced by the IBC for sealing certain mass timber interfaces. The other standards listed are not the prescribed comparative fire-resistance test for this determination.

References/Topics: 2021 IBC Sections 703.6 and 722.7.1; ASTM E119; UL 263; determination of noncombustible protection time contribution.

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The construction detail identifies a 1/2-inch tolerance between the steel beam web and the adjacent CLT panel. Therefore, option B is correct.

This is principally a construction-document interpretation question rather than a generic prescriptive IBC dimension. The 2021 IBC does not establish one universal steel-web-to-CLT clearance applicable to every mass timber connection. The required clearance is project specific and is established by the registered design professional through the approved structural drawings and connection details.

The tolerance provides erection clearance for placement of the prefabricated CLT around the steel member while accounting for fabrication and installation variation. It must not be arbitrarily reduced or increased because the gap can affect panel fit, bearing conditions, fastener alignment, fire-protection continuity, acoustic treatment and any specified joint-filling material.

Under the special-inspection framework, the inspector must compare the installed connection directly with the approved construction documents. Any condition that does not maintain the specified 1/2-inch clearance—or any undocumented field modification to the CLT or steel connection—must be reported and resolved through the registered design professional rather than accepted solely on the contractor’s direction.

References/Topics: Approved structural details; 2021 IBC Sections 1704.2 and 1705.5; inspection of mass timber erection, anchorage and connections.

ASTM E84 cannot be used to establish the hourly fire-resistance rating of a structural member or assembly. Therefore, option B is correct.

ASTM E84 evaluates surface-burning characteristics , principally flame-spread and smoke-developed indices. Those measurements characterize how a material ' s exposed surface behaves when subjected to the standard tunnel test. They do not demonstrate that a wall, floor, roof, beam, column, or structural assembly will maintain integrity and structural performance for one, two, or three hours.

Fire-resistance ratings are instead established through the methods recognized by the IBC, including standard fire testing—principally ASTM E119 or UL 263—prescriptive rated construction provided by Section 721, and calculated fire-resistance procedures under Section 722. The code also recognizes appropriately documented approved designs and other approved methods within the Section 703 framework.

This distinction is particularly important in mass timber work because ASTM E84 may appear elsewhere in the code for flame-spread limitations on materials, but an acceptable E84 result does not establish structural fire endurance.

The special inspector must determine which approved fire-resistance methodology applies and verify that the installed assembly precisely reflects that design.

References/Topics: 2021 IBC Sections 703, 721 and 722; ASTM E119; UL 263; distinction between fire resistance and ASTM E84 surface-burning testing.

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The IBC does not require structural composite lumber to retain the same nominal dimensions as the solid-sawn member it replaces. Instead, the minimum finished dimensions are determined from the heavy-timber dimensional equivalency provisions in Section 2304.11.

For a solid-sawn member having nominal dimensions of 8 inches by 8 inches, the corresponding minimum structural composite lumber net dimensions are 7 inches in width by 7-1/2 inches in depth. Therefore, option B is correct. The dimensional conversion recognizes that nominal solid-sawn dimensions differ from actual manufactured dimensions and that SCL products are produced to controlled net dimensions.

The 6-3/4-inch by 8-1/4-inch dimensions in option C correspond to the minimum glued-laminated timber equivalency for an 8-inch-by-8-inch nominal solid-sawn member, not the SCL equivalency. Option D incorrectly assumes that the SCL member must retain the original nominal dimensions, while option A does not match the required equivalency for either SCL or glued-laminated timber.

The substitution must also be approved by the registered design professional because dimensional compliance alone does not establish equivalent structural capacity, connection behavior, fire resistance, or load-path performance.

References/Topics: 2021 IBC Section 2304.11; heavy-timber minimum dimensions; minimum structural composite lumber net-size table.

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Mass timber can be incorporated into all five principal IBC construction types, although the extent and permitted application vary substantially. Therefore, option D is the technically complete answer.

Types III, IV and V provide the broadest opportunities for mass timber structural systems. Type III permits combustible interior building elements, Type IV is specifically organized around mass timber or noncombustible structural elements, and Type V permits structural elements of any material allowed by the code. Type IV includes the tall mass timber classifications IV-A, IV-B and IV-C, together with Type IV-HT.

Types I and II are predominantly noncombustible construction, but they are not absolute prohibitions against every wood or mass timber application. IBC Section 603 identifies permitted combustible materials in Types I and II. In addition, Table 601, Note c, permits heavy timber complying with Section 2304.11 for roof construction—including applicable primary structural frame members—where the required fire-resistance rating is one hour or less.

Consequently, the answer does not mean that a Type I or Type II building may be framed entirely with exposed mass timber. It means that code-compliant mass timber elements can be used in defined applications within each construction type.

References/Topics: 2021 IBC Sections 602.1–602.5 and 603.1; Table 601, Note c; Section 2304.11.

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The prescribed proportion is two-thirds , making option C correct. The relationship is demonstrated directly by IBC Table 722.7.1(1). A building element requiring a one-hour fire-resistance rating must receive 40 minutes of noncombustible protection; a two-hour element requires 80 minutes; and a three-hour-or-greater element requires 120 minutes. Each of those prescribed values represents two-thirds of the corresponding one-, two-, or three-hour rating.

For Type IV-A specifically, Section 602.4.1.2 requires protection of the interior faces of all mass timber elements. Section 602.4.1.2.1 further states that the protection must contribute at least the time assigned in Table 722.7.1(1) and not less than 80 minutes .

The remaining portion of the required fire resistance is provided by the mass timber element itself. Thus, for a three-hour Type IV-A primary structural element, 120 minutes are provided through noncombustible protection and the timber must supply the remaining required endurance.

This two-component approach is fundamental to the Type IV-A fire-design methodology.

References/Topics: 2021 IBC Sections 602.4.1.2 and 602.4.1.2.1; Tables 601 and 722.7.1(1); protected Type IV-A mass timber.

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ICC-ES ESR-1539 is the applicable evaluation report, making option C correct. ESR-1539 addresses nails and staples manufactured by participating companies and evaluates their use in engineered and nonengineered structural connections.

An ICC-ES Evaluation Report provides evidence that a proprietary product or system complies with specified building-code requirements where the product does not rely solely on the generic prescriptive provisions of the IBC. For proprietary nails, the report provides the technical basis needed to establish characteristics such as dimensions, materials, recognized structural applications, allowable design values, installation limitations, and conditions of use.

The current ICC-ES document is published as ESR-1539P, reflecting subsequent administrative updates to the report, but the identifying evaluation-report number remains 1539 , matching option C and the examination question.

For special inspection, merely recognizing the ESR number is not enough. The inspector should verify that the installed proprietary fastener is actually included in the report, that its diameter and length correspond to the approved construction documents, and that installation spacing, penetration, orientation, substrate, and other report conditions are satisfied.

References/Topics: ICC-ES ESR-1539, structural nails and staples; proprietary fastener evaluation and installation requirements. ICC-ES states that the nails and staples covered by ESR-1539 are used in engineered and prescriptive structural connections.

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).

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