International Code Council 93-Tall-Mass-Timber-Buildings 93-Tall-Mass-Timber-Buildings Exam Practice Test

The applicable requirement is found in 2021 IBC Section 504.3 and Table 504.3. The table regulates building height in feet above grade plane by occupancy, construction type, and sprinkler condition. For a Group I-4 occupancy equipped throughout with a Section 903.3.1.1 sprinkler system, the applicable row is the sprinklered “S” row.

Reading across that row to Type IV-B construction gives a maximum building height of 120 feet. Therefore, option B is correct. The 180-foot value applies to Type IV-A construction for the same occupancy and sprinkler condition. The 85-foot value, which is not offered, applies to Type IV-C and Type IV-HT. The 270-foot value generally appears for certain lower-hazard occupancies—such as Groups A, B, E, F, M, S and U—when constructed as sprinklered Type IV-A, but it is not permitted for Group I-4.

This distinction reflects the additional life-safety considerations associated with custodial-care occupancies. A special inspector should verify that the approved construction documents identify both the correct occupancy classification and construction type because either classification directly changes the permitted height.

References/Topics: 2021 IBC Section 504.3; Table 504.3, Group I-4, sprinklered Type IV-B construction; Section 903.3.1.1.

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Option A reproduces one of the two permitted exterior gypsum-board fastening methods in 2021 IBC Section 722.7.2.2. Type X gypsum board used as noncombustible protection on the exterior side of mass timber walls may be attached using galvanized nails of minimum 12 gage with a 7/16-inch head and sufficient length to penetrate the mass timber at least 1 inch .

The code also permits ASTM C1002 Type S, W, or G screws, but those screws must likewise penetrate the mass timber a minimum of 1 inch . Options C and D are therefore incorrect because they specify only 3/4-inch and 7/8-inch penetration, respectively. Option B is incorrect because it substitutes 16-gage nails for the minimum 12-gage requirement.

Section 722.7.2.2 additionally requires exterior Type X gypsum-board layers to be fastened 12 inches on center each way and 6 inches on center at joints or ends. Panel-edge fasteners must be located at least 1 inch and not more than 2 inches from the edge.

These fastening details are part of the conditions necessary to claim the protection contribution in Table 722.7.1(2).

References/Topics: 2021 IBC Sections 722.7.1 and 722.7.2.2; exterior Type X gypsum-board protection.

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The structural connections must maintain a fire-resistance rating corresponding to the required rating of the structural elements they connect. Because both the glulam beam and CLT panels require a two-hour fire-resistance rating, their connections must also provide two hours of fire resistance. Therefore, option C is correct.

Concealing steel hardware inside a timber member does not eliminate the fire-resistance requirement. Steel rapidly conducts heat and can lose strength, while timber surrounding a concealed connector can char, split, or withdraw from fasteners. The connection must consequently be protected through sufficient wood cover, noncombustible protection, tested assemblies, or an approved engineering analysis demonstrating acceptable connection temperatures and capacity for the entire required duration.

A three-hour rating is not required merely as a generalized safety factor; the code requires correspondence with the connected elements unless the approved design establishes another condition. A one-hour connection would create a premature weak point in the load path, and a zero-hour rating would be unacceptable simply because the hardware is hidden.

References/Topics: 2021 IBC Section 2304.10.1; fire-resistance rating of mass timber connections; protected concealed steel hardware.

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IBC Section 703.7 requires sealant or adhesive to resist air passage at the abutting edges and intersections of mass timber building elements where those elements are required to be fire-resistance rated. Section 1705.20 then requires periodic special inspection where those prescribed sealants or adhesives are installed. Option C repeats that first required location accurately.

Option D is defective because the code requires sealing at an intersection between mass timber and another material only where both intersecting building elements are required to be fire-resistance rated. The phrase “one or the other” materially weakens the condition. Option A is also too broad. A code-defined joint is not automatically subject to Section 703.7; fire-resistant joint systems are separately regulated by Section 715 and, where applicable, Section 1705.18.

Option B describes the exception in reverse. Sealant or adhesive need not be added under Section 703.7 where it is not a required component of the tested fire-resistance-rated assembly. When it is part of the listed or tested assembly, it must be installed accordingly, but that statement does not identify the primary location requested.

References/Topics: 2021 IBC Sections 703.7 and 1705.20; sealing of adjacent rated mass timber elements; periodic inspection.

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Minimum prescriptive dimensions are not themselves a component added into a calculated fire-resistance time. Therefore, option A is the exception.

IBC Section 602.4 states that a mass timber element’s required fire resistance can be based on the fire-resistance contribution of the mass timber, the noncombustible protection, or a combination of those two components. Options B, C, and D reflect those permitted approaches.

Minimum dimensions under Section 2304.11 serve a different function. They establish the minimum cross-sectional size and construction characteristics required for qualifying heavy timber or mass timber elements. A member can satisfy the minimum dimensional requirement without automatically achieving every required one-, two-, or three-hour fire-resistance rating. The structural fire calculation must evaluate the remaining effective section after charring, elevated-temperature effects, applied loading, and any credited protective materials.

The inspector must therefore verify both requirements independently: the installed member must meet the minimum code dimensions and must match the approved fire-resistance design. Increasing a member to the minimum prescriptive size does not by itself replace the required calculation, tested assembly, or approved protection system.

References/Topics: 2021 IBC Sections 602.4, 703.2, 722.7 and 2304.11; calculated mass timber fire resistance.

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Option B is correct because the required protection time placed over a mass timber structural connection may be established through a code-recognized fire-resistance evaluation of that protective construction under standard fire exposure.

IBC Section 2304.10.1 regulates connections in Types IV-A, IV-B, and IV-C. The code allows connection fire performance to be demonstrated through testing where the connection is incorporated into the fire-resistance test or through an approved engineering analysis. AWC further clarifies that the protection applied over the connection must provide the necessary protection time and that its performance may be established using the methods recognized by IBC Section 703.3, including testing and engineering analysis based on ASTM E119 or UL 263 performance.

Option A is too narrow: testing an isolated fastener does not establish the fire protection of the entire connection. Options C and D also use the wrong temperature location. Where an engineering-analysis route is used, the temperature criterion applies to the connection itself , including connectors, fasteners, and portions of wood incorporated into the structural connection—not simply to the protected structural element or supported member.

References/Topics: 2021 IBC Section 2304.10.1; Section 703.3; AWC guidance on fire resistance of mass timber connections.

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Option C correctly states the fundamental UL finish-rating criterion. UL defines a finish rating for assemblies containing combustible wood structural supports as the elapsed fire-exposure time at which the wood member immediately behind the protective membrane reaches the prescribed temperature-rise threshold.

More precisely, UL uses two criteria: an average temperature rise of 250°F or an individual-point temperature rise of 325°F , measured on the plane of the wood nearest the fire, typically between the gypsum membrane and the wood stud or joist. The question asks for the principal definition, which is the 250°F temperature-rise criterion; therefore, option C is correct. Option D incorrectly treats the 325°F individual-point limit as the sole definition.

Options A and B confuse a finish rating with “assigned protection time.” IBC Tables 722.6 and 722.7 provide calculated contribution values for specified protective materials, but those assigned values are not themselves UL finish ratings.

This distinction matters in mass timber fire design because membrane contribution, thermal separation, structural fire resistance, and finish rating are related but not interchangeable concepts.

References/Topics: UL Fire Resistance Directory terminology; finish rating; average 250°F and individual 325°F temperature-rise criteria.

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Option A is the incorrect statement and therefore the required answer. Under 2021 IBC Table 601, an exterior bearing wall in Type IV-C construction requires a two-hour fire-resistance rating , not one hour.

The tall mass timber classifications progressively vary the degree of noncombustible protection and allowable exposure, but the structural fire-resistance requirements remain substantial. Type IV-A exterior bearing walls require three hours. Type IV-B exterior bearing walls require two hours. Type IV-C exterior bearing walls also require two hours. Thus, options B, C, and D correctly reproduce the Table 601 values.

The special inspector must also recognize that Table 601 is not necessarily the only rating criterion affecting an exterior wall. Exterior walls are additionally subject to the requirements associated with fire separation distance, particularly Table 705.5. Where another IBC provision requires a higher rating, that more restrictive condition controls.

For mass timber construction, compliance also depends on the prescribed protective system, member dimensions, connections, joints, intersections, and exterior-side protection. A wall cannot be accepted as compliant solely because the timber cross section appears substantial; it must conform to the approved rated design.

References/Topics: 2021 IBC Section 601; Table 601; Section 602.4; Table 705.5.

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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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Option A is an exact requirement of the 2021 International Fire Code Section 3303.5 . For Type IV-A, IV-B, and IV-C buildings designed to exceed six stories above grade plane, standpipes must be provided in accordance with IFC Section 3313, unless otherwise approved by the fire code official.

The IFC also requires a water supply for fire department operations, but that supply must be approved by the fire code official and fire chief; the code does not specifically mandate that it be a “portable” water supply. Option B is therefore incorrect.

The remaining options alter important numerical requirements. Where noncombustible protection is required and construction exceeds six stories, at least one layer , not two, must be installed on applicable building elements more than four levels below active mass timber construction before additional floor levels are erected. Required exterior wall coverings are likewise required more than four levels below active mass timber construction, rather than two.

These safeguards reduce the amount of exposed combustible construction while ensuring that effective fire department infrastructure progresses with the building.

References/Topics: 2021 IFC Section 3303.5; Sections 3313 and related construction-stage fire protection requirements.

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The required minimum fire-resistance rating is two hours , making option C correct. Table 601 assigns a two-hour fire-resistance rating to the primary structural frame in Type IV-C construction. The structural connection between members of that rated frame cannot become a premature failure point in the load path.

IBC Section 2304.10.1 specifically addresses structural connections in Types IV-A, IV-B, and IV-C mass timber construction. Connection protection must provide the fire-resistance performance required for the connected building element. This can be accomplished through protected connection configurations, approved fire testing, or engineering analysis satisfying the applicable code criteria.

The connection includes more than the visible steel plate or bolt. Fasteners, connectors, concealed steel, bearing zones, and portions of the timber participating structurally in the connection must collectively maintain the required performance. A one-hour or 1½-hour connection would undermine a structural frame required to remain functional for two hours. Three hours is the primary-frame rating associated with Type IV-A, not the Type IV-C condition specified here.

The inspector should verify protection thickness, wood cover, gypsum layers, hardware embedment, edge conditions, and approved connection geometry before concealment.

References/Topics: 2021 IBC Table 601; Section 2304.10.1; fire-resistant structural connections in Types IV-A, IV-B, and IV-C.

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Option C is the incorrect statement. The sealing inspection requirements in IBC Section 1705.20 do not automatically apply to every item classified as a “joint” under Section 202. They apply specifically where a sealant or adhesive required by Section 703.7 is installed on mass timber building elements identified in the approved construction documents.

Section 703.7 addresses abutting edges and intersections of fire-resistance-rated mass timber elements and intersections between mass timber and other materials where both elements require a fire-resistance rating. These conditions require periodic special inspection because continuity of the air seal affects the fire performance assumed for the timber assembly.

Option A is correct: qualifying sealants must comply with ASTM C920. Option B is also correct: adhesives used for this purpose must comply with ASTM D3498. Option D reflects the required inspection of sealant applications at the prescribed abutting edges and intersections, although the technically precise term is “mass timber building elements.”

Fire-resistant joint systems are governed separately by IBC Section 715 and may require inspection under Section 1705.18. The two inspection categories must not be treated as interchangeable.

References/Topics: 2021 IBC Sections 703.7, 715, 1705.18 and 1705.20; ASTM C920; ASTM D3498.

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Section 602.4.2.2.2 permits unprotected mass timber ceilings in Type IV-B construction to equal no more than 20 percent of the floor area , and the code expressly states that attached beams are included when determining that exposed ceiling area.

The floor area is 900 square feet:

20% × 900 = 180 sq. ft. maximum exposed area .

The exposed 12-inch × 18-inch beam extends across the 30-foot room. Its three exposed surfaces consist of the 12-inch-wide bottom and two 18-inch-deep sides:

30 ft × (1 ft + 1.5 ft + 1.5 ft) = 120 sq. ft.

Because the attached beam counts against the ceiling exposure allowance, only:

180 − 120 = 60 sq. ft.

remains available for the exposed ceiling itself.

The exposed ceiling extends across the 30-foot room width, so:

30 ft × X = 60 sq. ft.

Therefore:

X = 2 ft .

Option A is correct. Ignoring the beam surfaces would overstate the permitted ceiling exposure and would contradict the explicit IBC requirement that attached beams be included in the exposed ceiling calculation.

References/Topics: 2021 IBC Section 602.4.2.2.2, Exception 1.1; Type IV-B exposed ceiling and attached-beam area calculations.

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A 7/16-inch wood structural panel is not one of the prescriptively acceptable fireblocking materials listed by IBC Section 718.2.1. Therefore, option C is correct.

Section 718.2.1 permits fireblocking to consist of several specified materials. These include one-half-inch gypsum board; properly secured batts or blankets of mineral wool, mineral fiber, or other approved materials; and mass timber complying with Section 2304.11. Options A, B, and D are consequently valid.

For wood structural panels, however, the IBC requires a substantially greater thickness: a single thickness of approximately 0.719 inch , conventionally represented as 23/32 inch, with joints backed by material of the same required thickness. A 7/16-inch panel is only approximately 0.438 inch thick and therefore does not satisfy that prescriptive fireblocking provision.

Fireblocking is intended to interrupt concealed draft openings and restrict the movement of flame and hot gases through concealed combustible spaces. It should not be confused with a tested firestop system used at penetrations through fire-resistance-rated assemblies.

Special inspection should confirm that the installed material, thickness, joint backing, retention, and location conform to the approved construction documents and the applicable code provision.

References/Topics: 2021 IBC Sections 718.2 and 718.2.1; Section 2304.11; permitted fireblocking materials.

The required minimum wood protection thickness is 1.75 inches , making option B correct. AWC Technical Report No. 10 establishes a thermal-separation methodology for protecting steel connectors and fasteners with sacrificial wood cover. Because the question specifies that the wood cover itself must provide the entire 60-minute fire-protection period, the protection thickness must be calculated using the thermal-separation provisions rather than relying on residual fire resistance from the connector or steel plate.

TR10 applies a reduction to the protection contribution of the base wood layer. Its connection examples use the relationship in Section 4.4.1.3, with the required thermal protection time divided by 0.85. For a 60-minute requirement, back-calculating the prescribed nonlinear wood charring equation gives approximately 1.71 inches of required wood thickness. The practical minimum corresponding to the available choices is therefore 1.75 inches.

The principle is critical for special inspection: steel connection components have high thermal conductivity and must remain below the temperature limits assumed by the connection fire design. The inspector must verify actual wood-cover thickness, fastening, continuity, and any gaps before concealment.

References/Topics: AWC Technical Report No. 10, Sections 4.4.1.3 and 4.5; connection thermal separation; wood protection of steel connectors. TR10 demonstrates the same calculation methodology for wood-covered steel connections.

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The intended code exception is shafts and vertical exit enclosures , making option B correct. The governing construction-phase provision is 2021 IFC Section 3303.5, which applies to buildings of Types IV-A, IV-B, and IV-C designed to exceed six stories above grade plane.

Where Section 602.4 of the IBC requires noncombustible protection, at least one layer must be installed on building elements located on floor levels—including mezzanines—more than four levels below active mass timber construction before additional floor levels can be erected. The provision is intended to prevent a tall mass timber project from accumulating an excessive number of substantially unprotected combustible stories during erection.

Section 3303.5 expressly states that shafts and vertical exit enclosures are not considered part of the active mass timber construction for application of this construction-progress requirement. Therefore, B is the examination answer.

Mezzanines are expressly included in the protected-level requirement. Required protection for floors, walls, and ceilings under IBC Section 602.4 progresses with construction subject to the IFC provision. The same section also requires standpipes, an approved water supply for fire department operations, and timely installation of required exterior wall coverings.

References/Topics: 2021 IFC Section 3303.5; 2021 IBC Section 602.4; fire safety during construction of tall mass timber buildings.

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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Option A is the exception because the base fire-resistance rating for an exterior bearing wall in Type IV-C construction is two hours, not one hour. The values are established by 2021 IBC Table 601.

Type IV-A has the most stringent tall mass timber construction requirements and assigns a three-hour rating to exterior bearing walls. Type IV-B and Type IV-C each assign a two-hour rating. Consequently, options B, C, and D accurately state the Table 601 requirements, while option A understates the required rating by one hour.

The Table 601 value is the minimum construction-type rating. Exterior bearing walls must also comply with the exterior-wall requirements of Table 705.5 based on fire separation distance. Where another code provision requires a higher rating, the more restrictive requirement governs. The inspector must therefore avoid treating the two-hour Type IV-C value as an absolute maximum.

Field verification should include the approved wall assembly, mass timber dimensions, noncombustible exterior protection, membrane continuity, protection of connections, intersections, joints, and any required opening protection. An exterior bearing wall installed as a nominal one-hour assembly would not comply merely because the timber itself has substantial cross-sectional dimensions.

References/Topics: 2021 IBC Table 601; Sections 602.4 and 705.5; exterior bearing-wall ratings for Types IV-A, IV-B, and IV-C.

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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.

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.

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IBC Table 601, Footnote “a,” permits a one-hour reduction in the required fire-resistance rating of the primary structural frame and bearing walls where those elements support a roof only. Option C is therefore correct.

For Type IV-C construction, the normal Table 601 requirement for bearing walls is two hours. Where a bearing wall qualifies as supporting only roof construction, application of the footnote permits that rating to be reduced from two hours to one hour.

The limitation “supporting a roof only” is critical. The reduction cannot be applied simply because a wall is located at the uppermost occupied level. If the wall carries a floor, mezzanine, transfer load, occupied rooftop structure, or another structural element beyond qualifying roof construction, the condition for the reduction is not satisfied.

Options A and B are not reductions prescribed by Table 601. Option D would effectively eliminate the entire normal two-hour Type IV-C bearing-wall rating, which the footnote does not permit.

For inspection purposes, the approved construction documents and structural load path must substantiate use of the reduction. The fire-protection installation should then be checked against the actual reduced rating specifically authorized by the design.

References/Topics: 2021 IBC Table 601, Footnote “a”; Type IV-C bearing walls supporting roof construction only.

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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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IBC Table 722.7.1(2) assigns a 40-minute protection contribution to 5/8-inch Type X gypsum board . Therefore, option D is correct.

The same table assigns 25 minutes to 1/2-inch Type X gypsum board. Consequently, option B overstates the protection contribution of the thinner Type X panel. Ordinary gypsum board values appearing elsewhere in Section 722 cannot simply be substituted for the specific mass timber noncombustible protection values in Table 722.7.1(2). Options A and C therefore do not state the protection contribution recognized by the mass timber table.

These assigned values are particularly important when multiple layers are required. For example, a two-hour building element requires at least 80 minutes of noncombustible protection under Table 722.7.1(1), which can be satisfied prescriptively with two properly installed layers of 5/8-inch Type X gypsum board, each contributing 40 minutes.

The contribution is valid only when the gypsum board is installed and fastened in accordance with Section 722.7.2.

References/Topics: 2021 IBC Tables 722.7.1(1) and 722.7.1(2); Section 722.7.2; Type X gypsum noncombustible protection.

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Type IV-B construction is fundamentally protected mass timber construction, but the 2021 IBC permits specifically limited areas of interior mass timber to remain exposed. Section 602.4.2.2.2 establishes two independent exposure limits. Unprotected portions of mass timber ceilings, including attached beams, are limited to 20 percent of the floor area of the dwelling unit or fire area. Unprotected portions of mass timber walls, including attached columns, are limited to 40 percent of that floor area . Accordingly, option C correctly states the permitted percentages.

These percentages do not operate in isolation. Exposed areas must also comply with Section 602.4.2.2.4, which establishes separation requirements between unprotected mass timber surfaces. Where both walls and ceilings are exposed within the same dwelling unit or fire area, Section 602.4.2.2.3 requires use of the mixed-unprotected-area equation rather than independently maximizing both percentages.

Option A describes neither Type IV-B nor its controlled-exposure concept. Option B incorrectly characterizes Type IV-B as requiring complete encapsulation. Option D reverses the ceiling and wall percentages.

References/Topics: 2021 IBC Sections 602.4.2.2.2, 602.4.2.2.3 and 602.4.2.2.4; Type IV-B permitted exposed mass timber.

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