93-Tall-Mass-Timber-Buildings 93-Tall-Mass-Timber-Buildings Questions and Answers

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.

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

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.

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

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.

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

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.

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

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.

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

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.

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

The minimum additional protection is 1/2-inch gypsum board or an approved equivalent thermal barrier , making option C correct.

The wall in the question functions as an occupancy separation. Under IBC Section 508.4.4.1, mass timber elements serving as fire barriers or horizontal assemblies separating occupancies in Type IV-B or IV-C construction must be separated from the building interior by an approved thermal barrier consisting of gypsum board at least 1/2 inch thick , or a material satisfying both applicable NFPA 275 thermal-barrier tests.

Because the wall separates two interior occupancies, each face is exposed to interior space; consequently, the thermal-barrier requirement applies to both surfaces .

This requirement must not be confused with the wall ' s two-hour fire-resistance rating. The underlying mass timber wall must independently satisfy the required two-hour assembly performance. The 1/2-inch gypsum protection is an additional thermal-barrier condition imposed because the rated separation is constructed of mass timber in Type IV-C.

Option D would provide substantially more gypsum protection than the specific occupancy-separation provision requires.

References/Topics: 2021 IBC Sections 508.4.4 and 508.4.4.1; Type IV-B/IV-C mass timber occupancy separations; approved thermal barriers; NFPA 275.

Yes. The allowance applies to both Type IV-B and Type IV-C construction , making option D correct.

IBC Section 508.4.4.1 regulates the construction of required separations between adjacent occupancies. Where the required separation is formed by a fire barrier or horizontal assembly, mass timber elements are specifically permitted to serve that function in Type IV-B or Type IV-C construction provided the mass timber is separated from the building interior by an approved thermal barrier.

The prescribed thermal barrier is gypsum board not less than 1/2 inch thick , or another material that has been tested and meets both the Temperature Transmission Fire Test and Integrity Fire Test acceptance criteria of NFPA 275.

The requirement is supplemental to the actual fire-resistance rating required for the occupancy separation. In other words, simply installing 1/2-inch gypsum board does not independently create the required fire barrier; the underlying mass timber assembly must also provide the applicable rated performance.

Type IV-HT is not included in this specific Section 508.4.4.1 mass timber allowance.

References/Topics: 2021 IBC Section 508.4.4.1; Type IV-B and IV-C occupancy separations; NFPA 275 thermal barriers.

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

The minimum required fire flow is 500 gallons per minute. Therefore, option C is correct.

Under 2021 IFC Section 3313.2, an approved water supply must be available when combustible building materials for the building under construction are delivered to the project site. The hydrant supplying the required flow must be located within the prescribed distance of the combustible materials as measured along an approved fire apparatus access route. Where one hydrant cannot provide coverage to all combustible material locations, additional hydrants are required.

The 500-gpm requirement is the initial minimum associated with the delivery of combustible building materials. It should not be confused with the potentially greater fire-flow requirements applicable after vertical construction of a Type III, IV, or V building begins. Depending on fire separation distance and the building’s calculated final fire-flow demand, a larger supply may be required under subsequent provisions.

Options A and B provide inadequate suppression capacity. Option D is not the baseline amount prescribed for the condition stated in the question. Inspectors and site safety personnel should verify that the water source is operational and accessible before substantial quantities of mass timber arrive on-site.

References/Topics: 2021 IFC Sections 3313.1 and 3313.2; construction-site water supply and combustible building materials.

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

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.

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

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.

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

The 1/2-inch lag screws attaching the structural steel ledger require fire protection, making option D correct. These fasteners are structural components of the ledger-to-CLT connection and therefore form part of the connection whose fire performance must be maintained for the required duration.

AWC Technical Report 10 states that wood structural connections—including their connectors, fasteners, and participating members—must be protected from fire exposure for the required fire-resistance time . Protection may be provided by wood cover, fire-rated gypsum board, other approved materials, or a combination.

TR10 distinguishes structural connection fasteners from small fasteners used merely to hold sacrificial protection in place. The report specifically explains that fasteners attaching protective wood strips need not themselves be protected, provided they are sufficiently long to keep the protection in position throughout the required exposure.

In the illustrated ledger connection, the 1/2-inch lag screws transfer structural load between the steel ledger and CLT wall. Their thermal protection is therefore integral to maintaining connection capacity.

References/Topics: AWC Technical Report No. 10 Sections 4.5 and connection examples; thermal protection of structural connectors and fasteners.

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

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.

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

Option D is the incorrect statement. IBC Section 722.7.2.1 requires the panel edges of the face layer , rather than the base layer, to be taped and finished with joint compound. Fastener heads on the face layer must also be covered with joint compound.

The other three provisions accurately reproduce the code. Each gypsum-board layer must be secured with Type S drywall screws long enough to penetrate the mass timber at least 1 inch when driven flush. Screws for the base layer are installed at 12 inches on center in both directions . Subsequent layers use the same general spacing but are offset from screws in the preceding layer. In addition, the panel edges of each succeeding layer must be offset 18 inches from the panel edges of the previous layer.

These details are not merely workmanship recommendations. They form part of the installation conditions under which the protection contributions in Table 722.7.1(2) can be credited.

References/Topics: 2021 IBC Section 722.7.2.1, Items 1–9; fastening, panel-edge offset, and finishing of Type X gypsum protection.

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

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.

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

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.

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

The IFC does not require daily inspection documentation to be stored in a fire- and water-resistant safe. Therefore, option C is the exception.

The owner or the owner’s authorized agent must establish and maintain the required construction-site fire-prevention program and designate a site safety director. The site safety director is responsible for completing a daily fire-safety inspection covering the building and exterior project areas. The results must be documented, retained on-site until the certificate of occupancy is issued, and made immediately available to the fire code official upon request. Options A, B, and D accurately reflect these administrative requirements.

The purpose is not merely record retention. Daily inspections are intended to identify conditions such as obstructed fire apparatus access, blocked hydrants or fire department connections, exposed temporary wiring, improper hazardous-material storage, uncontrolled combustible debris, unavailable extinguishers, impaired standpipes, and deficient hot-work controls.

A special inspector is not automatically the site safety director. However, observations involving installed passive protection or unsafe construction conditions should be communicated through the approved reporting process. The owner remains accountable for implementing the site safety plan and maintaining the required documentation.

References/Topics: 2021 IFC Sections 3303.1 through 3303.3; site safety director and daily fire-safety inspection records.

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

The code provides a specific combustible-material exception for qualifying water-resistive barriers , making option D correct. The exterior-protection provisions for Types IV-A, IV-B, and IV-C require the exterior side of mass timber walls to receive noncombustible protection with at least a 40-minute assigned protection time, and components of the exterior wall covering are generally required to be noncombustible.

A water-resistive barrier may be combustible only where it satisfies stringent fire-performance criteria. Among those criteria, the 2021 IBC limits peak heat-release rate and total heat release under ASTM E1354 and establishes flame-spread and smoke-developed limits under ASTM E84 or UL 723. The provision therefore does not create a blanket exemption for arbitrary combustible membranes.

Insulation, exterior cladding, and architectural components forming part of the regulated exterior wall covering must comply with the applicable noncombustibility requirements unless some other express code allowance applies. The WRB is the specifically identified exception tested by this question.

During inspection, product identification and fire-test documentation should be checked rather than assuming that a membrane qualifies merely because it is marketed as a water-resistive barrier.

References/Topics: 2021 IBC Sections 602.4.1.1, 602.4.2.1 and 602.4.3.1; exterior wall protection and qualifying water-resistive barriers.

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

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).

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

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 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.

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