Special Inspector 93-Tall-Mass-Timber-Buildings Syllabus Exam Questions Answers

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 illustrated wall corresponds to Type IV-A construction , making option A correct. The key indicator is the extensive Type X gypsum protection provided on the interior face of the CLT wall. Figure 63 shows multiple layers of 5/8-inch Type X gypsum board protecting the interior mass timber, together with the required exterior-side protection.

Type IV-A is the most comprehensively protected of the three tall mass timber construction classifications. IBC Section 602.4.1.2 requires the interior faces of all mass timber elements , including the inside face of exterior mass timber walls, to be protected with qualifying noncombustible material. Section 602.4.1.2.1 requires the protection contribution to satisfy Table 722.7.1(1) and never be less than 80 minutes. Type IV-A exterior walls also require at least 40 minutes of noncombustible protection on the outside face.

The three interior layers shown are consistent with a heavily protected Type IV-A rated wall. By contrast, Type IV-B permits limited exposed interior mass timber, while Type IV-C expressly permits mass timber interior elements to remain unprotected. Type IV-HT operates under fundamentally different heavy-timber provisions.

References/Topics: 2021 IBC Sections 602.4.1.1, 602.4.1.2 and 602.4.1.2.1; Tables 601 and 722.7.1(1)-(2).

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The figure depicts an unprotected portion of the mass timber ceiling . For Type IV-B construction, Section 602.4.2.2.2, Exception 1.1, limits unprotected ceiling areas—including attached mass timber beams—to 20 percent of the floor area of the applicable dwelling unit or fire area. Option B is therefore correct.

The percentage is based on floor area rather than total ceiling surface area. For example, where the associated fire area contains 1,000 square feet of floor area, the maximum ceiling exposure permitted under this particular exception would be 200 square feet, subject to the additional separation and mixed-exposure provisions.

The 40-percent value in option D applies to mass timber walls, including attached columns , rather than ceilings. The 15-percent and 30-percent values are not the prescribed Type IV-B ceiling exposure limitations in the 2021 IBC.

The inspector must additionally determine whether another exposed wall or ceiling region exists nearby. Section 602.4.2.2.4 imposes a 15-foot separation requirement, and Section 602.4.2.2.3 controls situations where both wall and ceiling surfaces are intentionally exposed.

References/Topics: 2021 IBC Sections 602.4.2.2.2 through 602.4.2.2.4; Type IV-B ceiling exposure limitations.

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A proprietary field-glued mass timber beam splice requires special inspection because the connection relies on a field-applied adhesive process that is not covered as a routine prescriptive mass timber connection in Table 1705.5.3. The controlling mechanism is IBC Section 1705.1.1, which authorizes the building official to require special inspection for unusual materials, systems, or installation procedures, particularly where compliance depends on additional manufacturer installation instructions.

The ICC code-development rationale for the tall mass timber provisions specifically identifies field-glued mass timber beam or panel splices as an example of work for which special inspection can be required. Inspection must address the approved evaluation report and manufacturer’s instructions, including substrate preparation, moisture and temperature limits, adhesive storage and expiration, mixing or proportioning, application quantity, open time, member alignment, clamping or pressure, and curing conditions.

Approval by the permit applicant has no regulatory significance. Verification by the registered design professional may supplement the inspection program but does not replace the approved special inspector. A building official may observe the work, but routine field verification by that official is not the prescribed quality-control procedure.

References/Topics: 2021 IBC Sections 1704.2, 1704.3 and 1705.1.1; special cases; proprietary field-glued mass timber splices.

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