Fire Resistance Of Concrete Masonry Construction

Concrete masonry, due to its inherent durability, reliability, and superior fire resistance characteristics, is well suited to a range of fire protection applications when complying with the life safety requirements of contemporary building codes. The International Building Code (IBC) (REF. 1) defines three wall types for fire protection — fire wall, fire barrier and fire partition — depending on the level of protection intended for the type of occupancy and intended use of the building. The key attributes of these three assembly types include:

• Fire Walls: Unless the entire building is constructed of combustible materials, fire walls are required to be constructed using noncombustible materials and thus provide the highest level of robustness and fire safety. During a fire, fire walls are also required to allow the collapse of the structure on either side without collapse of the fire wall itself. As such, fire walls effectively isolate and separate buildings or sections of a building.
• Fire Barrier: Fire barriers have less stringent code requirements compared to fire walls and are typically used to separate sections within a building, such as the walls of a stairwell shaft, to compartmentalize the building and allow for safe egress during a fire.
• Fire Partitions: Compared to fire walls and fire barriers, fire partitions generally offer less fire protection and are generally designed to limit the spread of fire within a given area of a building.

Designing and detailing for fire safety is a complex task with many facets, including addressing structural stability, fire resistance, vertical and horizontal continuity, and protecting openings and penetrations in walls. It is beyond the scope of this Tech Note to include every code provision and exception for fire safety design for all project conditions. As such, the information contained herein should be reviewed carefully to ensure conformance to local building code requirements and project-specific needs. In addition, the details shown here may not be the only ones that will comply with stipulated performance objectives but are included as examples. Project-specific needs will dictate the final detailing decisions.

SOLUTIONS SUMMARY

Building codes take a multifaceted approach to protecting life and property during a fire. These requirements address the combustibility, flame spread, smoke release, and structural stability of the systems used to mitigate the occurrence and spread of fire within buildings while allowing the safe evacuation of occupants when necessary. The inherent attributes of concrete masonry make it an ideal choice in meeting and exceeding the minimum building code requirements. The fire resistance of concrete masonry assemblies is most commonly determined using the equivalent thickness method. This calculation procedure accommodates a nearly limitless combination of unit sizes and configurations, combined with an array of aggregate types used in producing the concrete masonry units, to determine the fire resistance of the completed concrete masonry assembly, as shown in TABLE 1 below:

1.0 BALANCING FIRE DESIGN OBJECTIVES

The application of balancing fire design objectives can vary based on project-specific requirements, but they generally include addressing each of the following:

• Mitigating the formation of fires by controlling potential sources of ignition and fuel loads within buildings.
• Use of sensors to detect heat, smoke, flame, or gas to warn occupants and permit a safe evacuation.
• Installing automatic sprinkler system to control a fire at its point of origin.
• Limit the spread of fire and smoke through compartmentation and provide occupants with a safe egress path during an evacuation.

Each of these design considerations targets a different aspect of the broader fire safety objectives of building codes. Of each of these topics, however, only compartmentation is considered a passive fire safety strategy, whereas mitigation, detection, and suppression strategies require maintenance, are subject to human error or neglect, or rely on equipment that may be faulty. As such, addressing each of these aspects ensures the highest level of life safety and property protection.

2.0 FIRE-RESISTANCE RATINGS OF CONCRETE MASONRY ASSEMBLIES

A common feature of all wall assemblies that form a part of a building’s fire safety system is that they must have a fire resistance rating, which varies depending on the use, siting, size and other building variables. In accordance with the IBC, the fire resistance of concrete masonry assemblies can be determined through one of multiple compliance options. These include:

• Physical evaluation in accordance with ASTM E119, Standard Test Methods for Fire Tests of Building Construction and Materials (REF. 2) or UL 263, Fire Tests of Building Construction and Materials (REF. 3). While two distinct standards, the testing procedures outlined in ASTM E119 and UL 263 are nearly identical, and as such produce very similar fire-resistance ratings for concrete masonry assemblies. Full-scale testing may also be associated with a listing service such as UL Solutions or FM Global (REF. 4).
• Calculated fire resistance determined in accordance with Section 722 of the IBC. The calculated fire-resistance method is an adaptation of the standard ACI/TMS 216.1, Code Requirements for Determining Fire Resistance of Concrete and Masonry Construction Assemblies (REF. 5). The calculated fire resistance is derived from hundreds of tests conducted on concrete masonry assemblies tested in accordance with ASTM E119.
• Prescriptive detailing requirements in accordance with Section 721 of the IBC. These include commonly used concrete masonry wall assemblies that are deemed to comply with a prescribed level of fire resistance based on historical testing in accordance with ASTM E119 or UL 263.
• Alternative modeling or designs based upon engineering analyses or alternative sources of documentation, research or testing.

Private commercial listing services allow the designer to select a fire-rated assembly that has been previously tested, classified and listed in a published directory of fire-rated assemblies. The listing service also monitors materials and production to verify that the concrete masonry units are and remain in compliance with appropriate standards, which usually necessitates a premium for units of this type. The system also is somewhat inflexible in that little variation from the original tested wall assembly is allowed, including unit size, shape, mix design, constituent materials and even the plant of manufacture.

Further, because full-scale fire testing of representative test specimens is not practical in daily practice due to time and financial constraints, the calculation method is the most commonly applied option for determining the fire-resistance rating of concrete masonry assemblies. The calculation method is based on extensive testing and research that established relationships between the physical properties of the concrete masonry used to construct an assembly and the resulting fire-resistance rating of that assembly

2.1 Calculated Fire-Resistance Ratings – Wall Assemblies

The calculated fire resistance of concrete masonry wall assemblies is based on the results of hundreds of full-scale tests conducted in accordance with the ASTM E119, which measures four performance criteria during the course of the test:

• Resistance to the transmission of heat through the wall assembly
• Resistance to the passage of hot gases through the wall, sufficient to ignite cotton waste
• Load-carrying capacity of load-bearing walls
• Resistance to the impact, erosion and cooling effects of a hose stream on the assembly after exposure to the standard fire

An assembly must successfully pass each of these performance criteria for the duration of the assigned rating period. The fire resistance rating of concrete masonry is typically governed by the heat transmission criteria. From the standpoint of life safety (particularly for firefighters) and salvageability, this failure mode is preferable to a structural collapse endpoint, characteristic of many other building materials.

The two key design variables that influence the calculated fire resistance of a concrete masonry assembly include:

• The type of aggregate used in the production of the concrete masonry unit, recognizing that different aggregate types have different thermal conduction properties. The aggregate categories are listed in TABLE 1 in the Solutions Summary section. For aggregates not listed in TABLE 1, full-scale fire testing is usually required (REF. 26). Because the availability of specific aggregate types varies from region to region, it is best practice to simply specify the minimum fire-resistance rating and not a specific aggregate type unless that aggregate type is known to be available in the region.
• The equivalent thickness of the concrete masonry unit. Equivalent thickness is the solid thickness that would be obtained if the volume of concrete contained in a hollow unit were recast without core holes, as illustrated in FIGURE 1. The equivalent thickness is determined in accordance with ASTM C140/C140M, Standard Test Methods for Sampling and Testing Concrete Masonry Units and Related Units (REF. 6), and is reported on the ASTM C140 test report. If the equivalent thickness is unknown, but the percent solid of the unit is known, the equivalent thickness of a hollow unit can be determined by multiplying the percent solid by the unit’s actual thickness.

Estimated equivalent thickness values for typical two-cell, three-web concrete masonry units are provided in TABLE 2. The equivalent thickness of a 100% solid unit or an assembly where all cells are filled with an approved material is equal to the actual unit thickness.

Applying the information in TABLE 1, the fi re-resistance rating of a nominal 10 in. (254 mm) concrete masonry unit meeting the requirements of ASTM C90 and manufactured using expanded clay aggregate can be determined. Based on the results of ASTM C140 testing, these units have an actual measured thickness of 9.64 in. (245 mm) and are 47% solid. The resulting equivalent thickness (Te) of these units is then:

From TABLE 1, the fi re-resistance rating of a concrete masonry unit manufactured with expanded clay aggregate and having an equivalent thickness of 4.5 in. (114 mm) is halfway between 3 and 3.25 hours, or approximately 3.1 hours.

2.1.1 Cell Fill Materials

ACI/TMS 216.1 includes several options for increasing the equivalent thickness of the assembly when all open cells are filled with an approved material. When only a portion of the open cells are filled with an approved material (such as this case for partially grouted construction), the equivalent thickness of the assembly is taken equal to the equivalent thickness of the concrete masonry unit.

If all cells of hollow unit masonry are filled with an approved material, the equivalent thickness of the assembly is the actual thickness. This also applies to partially grouted concrete masonry walls where all ungrouted cells are filled with an approved material. Cell fill materials recognized by ACI/TMS 216.1 include: grout meeting the requirements of ASTM C476 (REF. 13); sand, pea gravel, crushed stone or slag aggregates that comply with ASTM C33 (REF. 14); pumice, scoria, expanded shale, expanded clay, expanded slate, expanded slag, expanded fly ash or cinders that comply with ASTM C331 (REF. 15); perlite meeting the requirements of ASTM C549 (REF. 16); or vermiculite complying with C516 (REF. 17). The use of other materials to fill the cells of concrete masonry construction (such as foam plastic insulation) does not impact the calculated fi re resistance of the assembly. More information on code requirements for protection of foam plastic insulation in walls can be found in Section 6.

Returning to the previous example of the nominal 10 in. (25 mm) concrete masonry unit produced using expanded clay aggregate, if an assembly constructed with these units were to be solid grouted, the resulting equivalent thickness would be taken equal to the actual unit thickness, or 9.64 in. (245 mm). From TABLE 1, the minimum required equivalent thickness for a 4-hour fire rating is 5.1 in. (130 mm). Because building codes do not stipulate fire-resistance periods exceeding 4 hours, the rating of this assembly would be reported as 4 hours, recognizing that its actual performance would exceed this rating.

2.1.2 Blended Aggregate Concrete Masonry Units

Rarely are concrete masonry units produced using a single aggregate type, but instead a combination of two or more aggregate types to achieve targeted unit properties such as unit density, compressive strength or desired aesthetic. Per Footnote B of TABLE 1, the equivalent thickness of units manufactured with a blend of different aggregate types is determined based on the proportion of each aggregate type used. This can be expressed by EQUATION 1.

For example, the required equivalent thickness of an assembly constructed of units made with expanded shale (80% by volume), and calcareous sand (20% by volume), to meet a 3-hour fi re-resistance rating is determined as follows: from TABLE 1, the equivalent thickness required for a unit produced using expanded shale for a 3-hour rating (T1) is 4.4 in. (112 mm). Similarly, the equivalent thickness required for a unit produced using calcareous sand for a 3-hour rating (T2) is 5.3 in. (135 mm). The resulting required minimum equivalent thickness for the 80%/20% blend of expanded shale and calcareous sand is then:

2.1.3 Multi-Wythe Wall Assemblies

The fire-resistance rating of multi-wythe walls consisting of two or more wythes of masonry is determined using the fire-resistance rating of each wythe plus the contribution of the continuous air space between each wythe of masonry, provided that the thickness of the air space is at least 0.5 in. (13 mm) and not more than 3.5 in. (89 mm). The combined fi re-resistance rating of a multi-wythe assembly (Rmw) is determined using EQUATION 2.

When the multi-wythe wall is constructed using a combination of concrete and clay masonry units, as illustrated in FIGURE 2, then the fire-resistance rating of the clay masonry wythe needs to be determined in accordance with TABLE 3. In applying Equation 2, it does not matter which wythe of masonry is exposed to the fire.

Consider a multi-wythe assembly constructed with a concrete masonry backing having a fire-resistance rating of 1.8 hours (R₁) and a clay brick veneer having a fire-resistance rating of 1.2 hours (R₂) separated by a 1 in. (25 mm) continuous airspace (A1 = 0.30). The resulting fire rating of this combined assembly is calculated as:

The majority of multi-wythe masonry walls will have calculated fire-resistance ratings that exceed the maximum 4-hour requirement by most building codes. As such, the rating of these assemblies would generally be reported as 4 hours.

2.2 Concrete Masonry Columns

Concrete masonry column fire testing evaluates the ability of the column to carry design loads under standardized fire test conditions. Based on a compendium of fire tests, the fire-resistance rating of reinforced concrete masonry columns is based on the least plan dimension of the column as indicated in TABLE 4. The minimum required cover over the vertical reinforcement is 2 in. (51 mm).

2.3 Concrete Masonry Beams (Lintels)

Fire testing of concrete masonry beams and lintels evaluates the ability of the member to sustain design loads under standardized fire test conditions. This is accomplished by ensuring that the temperature of the tensile reinforcement does not exceed 1,100°F (593°C) during the rating period.

The calculated fire-resistance rating of concrete masonry lintels is based on the nominal thickness of the lintel and the minimum cover of longitudinal reinforcement as summarized in TABLE 5. The cover requirements protect the reinforcement from strength degradation due to excessive temperature during the fire exposure period. Cover requirements may be provided by masonry units, grout or mortar. When reinforcement is not necessary for spanning an opening, such as when masonry arches are used, limiting the temperature rise in the reinforcement is not relevant.

2.4 Steel Columns Protected by Concrete Masonry

Fire testing of a steel column protected by concrete masonry evaluates the structural integrity of the steel column under fire test conditions by measuring the temperature rise of the steel. Input variables needed to calculate the fi re protection provided by wrapping steel columns in concrete masonry (Rsc) include the perimeter of the steel column (ps), the cross-sectional area of the steel column (Ast), the thermal conductivity of the concrete masonry (kcm), the density of the concrete masonry (wcm), and the interior perimeter of the concrete masonry protection (p), as expressed in EQUATION 3.

2.5 Effects of Finish Materials on Fire-Resistance Ratings

When drywall, plaster, or stucco finishes are used on concrete masonry walls, the IBC and ACI/TMS 216.1 include provisions accounting for the additional fire resistance provided by these materials. When finishes are accounted for in determining the fire rating of the assembly, the masonry alone must provide at least one-half of the total required rating, and the contribution of the finish on the non-fire-exposed side cannot be more than one-half of the contribution of the masonry alone. This is to ensure the masonry provides the necessary structural integrity during a fire.

Certain finishes deteriorate more rapidly when exposed to fire compared to when they are on the non-fire side of the wall. For finishes on the non-fire-exposed side of the wall, the finish is converted to an equivalent thickness of concrete masonry by multiplying the finish thickness by the factor given in TABLE 6. The resulting equivalent thickness of the finish (Tef) is then added to the concrete masonry wall equivalent thickness (Te) and used in TABLE 1 to determine the fire-resistance rating of the assembly.

For finishes on the fire-exposed side of the wall, a time is assigned to the finish in accordance with TABLE 7. This time is added to the fire-resistance rating determined for the base wall and non-fire-exposed side finish, if any. The times listed in TABLE 7 are essentially the length of time the various finishes will remain intact when exposed to fire on the fire-exposed side of the wall.

Unless the building code stipulates that the assembly only needs to be rated for fire exposure from one side of the wall, these two checks are performed assuming each side of the wall is the fire-exposed side. The resulting fire rating of the wall assembly is the lower of these two values.

For example, consider a concrete masonry assembly manufactured with limestone aggregate having an equivalent thickness of 3.9 in. (99 mm). Interpolating the fire-resistance rating of this unit from TABLE 1, the result is 1.92 hours. Inaddition to the rating provided by the base concrete masonry assembly, if one side of this assembly is to receive a 0.75 in. (19 mm) coating of a portland cement-sand plaster and the other side finished with a 0.5 in. (13 mm) layer of gypsum wallboard, the resulting fire-resistance rating of the assembly would be that which yields the smaller rating period considering the fire occurring on either side of the assembly (unless the assembly is only required to be rating for fire exposure from one side).

Assuming the fire occurs on the portland cement-sand plaster
side of the wall, the total wall assembly fire resistance is
determined as follows:

• Per TABLE 6, the multiplying factor for a 0.5 in. (13 mm) thick gypsum wallboard finish (non-fire-exposed side) installed over concrete masonry produced using limestone aggregate is 3.00. The resulting equivalent thickness of this stucco finish is then: (0.5 in.)(3.00) = 1.5 in. (38 mm). This gives a total equivalent assembly thickness of (3.9 in.)+(1.5 in.) = 5.4 in. (137 mm). Interpolating from TABLE 1, the fire-resistance rating for this composite block-stucco assembly would be 3.42 hours.
• Similarly, per TABLE 7, the increase in fire resistance for a 0.75 in. (19 mm) portland cement-sand plaster (fire-exposed side) is 20 minutes, or 0.33 hours. Adding this increase to the previously calculated rating of 3.42 hours: (3.42 hours)+(0.33 hours) = 3.75 hours.
• Repeating the above checks, but now assuming the gypsum wallboard side of the assembly will be exposed to fire:
• From TABLE 6, the multiplying factor for portland cements and plaster installed over limestone concrete masonry units is 1.00. Therefore, the equivalent thickness of the stucco finish is: (1.00)(0.75 in.) = 0.75 in. (19 mm). This gives a total equivalent assembly thickness of (3.9 in.)+(0.75 in.) = 4.6 in. (117 mm). Interpolating from TABLE 1, the fire-resistance rating for this composite block-stucco assembly would be 2.58 hours.
• Per TABLE 7, the increase in fire resistance for a 0.5 in. (13 mm) gypsum wallboard (fire-exposed side) is 15 minutes, or 0.25 hours. Adding this increase to the previously calculated rating of 2.58 hours: (2.58 hours)+(0.25 hours) = 2.83 hours.

Because it generally isn’t known which side of an assembly will be exposed to fire, the lower fire-resistance rating will control the design. In this example, the governing fire rating is 2.8 hours.

Finishes that are assumed to contribute to the total fire-resistance rating of a wall must be continuous over the surface to which it is applied and installed in accordance with the requirements set forth by the building code. Gypsum wallboard may be furred or attached directly to the masonry wall using adhesive and fasteners. When furring members are used with gypsum wallboard, the spacing of the furring is limited to 24 in. (610 mm) and fastened using self-tapping drywall screws spaced 12 in. (305 mm) on center along the length of the furring strips. When gypsum wallboard is adhered to the masonry
backing, it is secured in place using at least one masonry nail for each 2 ft² (0.19 m₂) of panel surface.

3.0 STRUCTURAL STABILITY OF FIRE WALLS

Fire walls, fire barriers, and fire partitions are required to have the minimum fire-resistance rating and continuity stipulated by the building code for the intended use and occupancy of the building. Because of their unique role in separating buildings or sections of buildings, fire walls must have sufficient structural stability under fire conditions to remain standing for the duration of time indicated by the fire-resistance rating, even with the collapse of construction on either side of the fire wall.

Because most design criteria relating to the fire-resistance rating, protection of openings and penetrations, and vertical and horizontal continuity are prescriptive, the primary challenge when designing and detailing a concrete masonry fire wall relates to maintaining the structural stability of the wall under fire conditions. There are various methods of designing, detailing and constructing fire walls for structural stability during a fire, including: (a) cantilevered or freestanding walls, (b) laterally supported and tied walls, and (c) double-wall construction.

3.1 Cantilevered and Freestanding Fire Walls

Cantilevered walls do not depend on the floor or roof framing for structural support. The wall is cantilevered from the foundation by grouting and reinforcing, or by prestressing. Freestanding walls also do not require support from the floor or roof but are instead designed to span horizontally between pilasters or masonry columns integral to the wall, as illustrated in FIGURE 4.

Thermal expansion of the adjacent floor or roof system during a fire can result in additional loads being applied to the wall, which must be considered when designing and detailing both the floor/roof as well as the concrete masonry wall. Cantilevered walls also often require substantial foundations to accommodate lateral wind or seismic loads. As such, cantilevered walls may not be ideal for all projects, particularly for very tall walls or where poor soil conditions exist.

3.2 Laterally Supported Fire Walls

Laterally supported fire walls are anchored to the roof or floor that they vertically support, which in turn provides lateral support to the fire wall. As with any fire wall, adequate clearance between the framing and the concrete masonry fire wall is necessary to allow for framing expansion or deformation without exerting unaccounted-for loads onto the wall.

Laterally supported fire walls generally fall into two different categories:

• Break-Away: These types of fire walls are designed and detailed similarly to non-rated assemblies, except they utilize break-away connectors to anchor the masonry to the roof/floor system. Break-away anchors are manufactured with metals having melting points lower than structural steel (generally about 800 °F (427 °C)), so that in the event of fire, the connectors on the side of the wall subject to fire will fail before those on the non-fire side, allowing the roof/floor system on the side of the wall to fall free of the fire wall. FIGURES 5-7 illustrate examples of detailing load-bearing and non-load-bearing laterally supported fire walls.
• Tied: Tied fire walls are a type of laterally supported fire wall where the floor/roof structure is not supported by the fire wall; instead, the floor/roof structure on each side of the fire wall supports the roof/floor structure on the opposite side. Thus, the two floor/roof structures are tied together across the fire wall. Tied fire walls require the floor/roof system on the non-fire-exposed side of the assembly to resist the forces generated due to the collapsing floor/roof assembly on the fire-exposed side of the fire wall. FIGURE 8 illustrates detailing options for tied fire walls. FIGURE 8A illustrates a double-column detail that uses a through-wall tie to connect the primary steel on both sides of the fire wall. In this detail, the primary framing steel is parallel to the fire wall and supported on fire-proofed columns. One column is used on each side of the fire wall to support the roof system for that portion of the building. Both steel columns and primary support beams/trusses should be aligned vertically and horizontally with the columns and beams/trusses on the opposite side of the wall. If the primary steel is not parallel to the fire wall, FIGURE 8B shows a through-wall tie that can be used.

As an alternative to using two steel columns, FIGURE 8C shows one steel support column encased entirely within the concrete masonry fire wall. Methods of calculating the fire resistance provided by the concrete masonry enclosure are covered in the steel column fire protection section. This system creates a single column line tied at the top of the wall to the horizontal floor/roof framing. Detailing the connection of the steel beams to the concrete masonry fire wall varies based on the framing layout, but the wall must be supported at the top and the connection must be fire protected.

3.3 Double Fire Walls

Double fire walls utilize two independent concrete masonry walls side by side, each meeting the required fire-resistance rating as shown in FIGURE 9. These assemblies are generally easier to design and detail for load-bearing conditions, especially for taller walls, but do require more interior space and materials. In the event one wall is pulled down due to fire, the other wall remains intact, preventing fire spread. Floor and roof connections to each fire wall are the same as for conventional concrete masonry construction.

4.0 FIRESTOPPING AND PENETRATION PROTECTION

In most applications, various conditions require joints or penetrations in rated assemblies, including movement joints, utility penetrations, floor/wall intersections and electrical outlets.Regardless of the type of penetrating item, gap or joint, the IBC requires that the continuity of the fire-resistant or smoke-resistant assembly be maintained with firestopping. A firestop system is an assemblage of specific materials or products used in conjunction with a rated assembly to resist the spread of fire for a prescribed time. These systems may be prescriptively designed or may be a tested/rated system.

When extending the continuity of the wall to and through the penetrating item or items, the appropriate firestop system must be selected. Key considerations include: 1) accommodating any anticipated movement, either of the penetrating item or between the penetrating item and the concrete masonry assembly; and 2) material compatibility between the firestop material, the penetrating item and the concrete masonry assembly. Without proper system selection and installation, the continuity of the fire-resistance-rated assembly can be compromised.

4.1 Through Penetrations

When the penetrating item is a steel, ferrous or copper material,
Chapter 7 of the IBC permits the annular space between the
rated concrete masonry assembly and the penetrating item to
be filled with concrete, grout or mortar provided that:

• The penetrating item has a maximum nominal diameter of 6 in. (152 mm)
• The area of the opening through the rated assembly does not exceed 144 in.² (0.09 m₂)
• The concrete, mortar or grout is installed for the full thickness of the rated assembly or the thickness required to maintain the fire-resistance rating of the assembly

FIGURE 10 illustrates this method of detailing around a through-wall penetration. In cases where the penetrating item is contained in a sleeve, the annular space includes the space between the penetrating item and the sleeve as well as the space between the sleeve and wall assembly. If one or more of these conditions for using mortar, grout or concrete around a penetration are not met, then the fi restop system must be tested in accordance with ASTM E814, Standard Test Method for Fire Tests of Penetration Firestop Systems (REF. 28), UL 1479, Fire Tests of Through-Penetration Firestops (REF. 18) subjected to a minimum positive pressure differential of 0.01 in. (2.49 Pa) of water, an approved assembly tested in accordance with ASTM E119 (REF. 2), or a building official-approved alternative per Chapter 1 of the IBC.

4.2 Membrane Penetrations

Membrane penetrations are those that penetrate only one side of a rated assembly, such as the opening for an electrical outlet. The IBC language for protecting membrane penetrations is very similar to that for through penetrations. However, there are specific prescriptive criteria that address electrical boxes no larger than 16 in.² (0.0103 m₂) in fire walls with a fire-resistance rating up to two hours. These criteria are shown in FIGURE 11 and address the maximum area of openings, the annular space between the wall and the box, and separation or protection of such boxes when installed on opposite sides of the wall.

4.3 Duct Penetrations

Non-dampered ducts that penetrate fire-rated walls must comply with the requirements for through penetrations. Dampered ducts and air transfer openings are tested to either UL 555, Standard for Fire Dampers (REF. 30) or UL 555S, Standard for Smoke Dampers (REF. 31), or both for fire/smoke dampers. Fire and smoke dampers must be tested according to the standards listed above, as there are no prescriptive damper treatments that are deemed to comply with the IBC.

4.4 Joint Protection

Per the IBC, any joint in or between rated walls, floors or roofs is required to provide a fire-resistance rating at least equal to that of the wall, floor or roof in or between which it is installed. Fire-resistant joint systems must be tested in accordance with the requirements of either ASTM E1966, Standard Test Method for Fire-Resistive Joint Systems (REF. 32), or UL 2079, Standard for Tests for Fire Resistance of Building Joint Systems (REF. 33).

Prescriptive requirements for maintaining the fire resistance of control joints are included in ACI/TMS 216.1 (REF. 5), which is adopted by reference in the IBC. The details are covered in CMU-TEC-009-23, Crack Control Strategies for Concrete Masonry Construction (REF. 34).

5.0 PROTECTING FOAM PLASTIC INSULATION

Foam plastic insulation is often used in exterior concrete masonry construction to improve steady-state thermal performance (R-value), and, in some cases, to improve air and moisture infiltration properties. Because of their potential flammability and smoke generation in the event of a fire, the IBC imposes additional requirements on these materials when they are used in exterior walls.

Foam plastic insulations include both rigid board (expanded polystyrene, extruded polystyrene, polyisocyanurate) as well as open-cell and closed-cell spray-applied polyurethane foam insulations and injection-applied aminoplast foam insulations. These insulation materials may be used on the interior or exterior surface of the masonry or in the cores (as either inserts or foam) of single-wythe masonry walls and in the cavities of masonry cavity walls. Because these types of insulation are flammable, the IBC mandates that they be protected to prevent the plastic insulation from contributing to the spread of fire in a building.

These requirements do not apply to mineral-based insulation
materials.

The performance of wall assemblies containing plastic insulation is evaluated in accordance with NFPA 285, Standard Fire Test Method for Evaluation of Fire Propagation Characteristics of Exterior Non-Load-Bearing Wall Assemblie Containing Combustible Components (REF. 35). NFPA 285 addresses the possibility of fire entering wall cavities through door or window openings, igniting foam plastic insulation, and spreading vertically to upper stories. As such, the IBC
requirement for testing under NFPA 285 generally applies to all types of construction, with a few exceptions for single-story and combustible construction.

The IBC stipulates that plastic insulation be separated from the interior of a building by a thermal barrier, which can be satisfied by a 1 in. (25 mm) minimum thickness of masonry or concrete. The IBC also requires ignition testing of plastic insulation used in exterior walls, although assemblies protected with at least 1 in. (25 mm) of concrete or masonry on the exterior are exempt from testing.

Further, concrete masonry assemblies are exempt from testing in accordance with NFPA 285 when one of the following two conditions is met:

1. Wall assemblies where the foam plastic insulation is covered on each face by a minimum 1 in. (25 mm) thickness of masonry or concrete and meeting one of the following:
   • There is no air space between the insulation and the concrete or masonry.
   • The insulation has a flame spread index of not more than 25 as determined in accordance with ASTM E84 (ref. 36) or UL 723 (ref. 37), and the maximum airspace between the concrete or masonry is not more than 1 in. (25 mm).
2. One-story buildings meeting the following conditions: the thickness of the insulation is not more than 4 in. (102 mm); the foam plastic has a flame spread index of 25 or less and a smoke-developed index of 450 or less; the plastic insulation is covered by aluminum (at least 0.032 in. (0.81 mm) thick) or corrosion-resistant steel (at least 0.0160 in. (0.406 mm) thick), provided that the insulation is not thicker than 4 in. (102 mm), and that the building is equipped with an automatic sprinkler system.

Note that TMS 402/602 requires a minimum 1 in. (25 mm) drainage space for anchored veneers. Consideration should be given for complying with these requirements as well as the exceptions above for NFPA 285 testing.

Sections 5.1, 5.2 and 5.3 review various options for complying with the IBC requirements and NFPA 285 performance objectives when the deemed-to-comply options are not applicable.

5.1 Single-Wythe Concrete Masonry Walls

Single-wythe walls may incorporate foam insulation in the cores of the masonry units as either rigid foam inserts or foamed-in-place insulation. To protect the insulation from fi re exposure, the IBC requires a minimum of 1 in. (25 mm) of concrete or masonry on the interior and exterior of the foam insulation. Because 6 in. (152 mm) concrete masonry units have a minimum face shell thickness of 1 in. (25 mm) and 8 in. (203 mm) and larger concrete masonry units have a minimum face shell thickness of 1.25 in. (32 mm) (REF. 9), this requirement is satisfied by the face shells of the concrete masonry units.

At openings, however, the insulation in the cells of single-wythe construction must also be protected at the jamb locations. Along the vertical sides of an opening, the end cell can be grouted, which also provides an anchorage location for the door or window. For the horizontal jamb, the top and bottom of the opening can be protected by the masonry or precast lintel above and the sill below, as illustrated in FIGURE 12. Provided the thickness of this protection is 1 in. (25 mm) or greater, the insulation is fully encapsulated, and the intent of the IBC is met.

5.2 Multi-Wythe Concrete Masonry Walls

Multi-wythe concrete masonry construction is most commonly masonry cavity walls, which often incorporate foam plastic insulation in the cavity formed by the two masonry wythes. In this case, there is more than 1 in. (25 mm) of masonry on both the interior and exterior; therefore, the focus is on protecting the insulation at opening locations.

FIGURE 13 shows a window top-of-opening detail in a concrete masonry cavity wall. In this scenario, 1 in. (25 mm) of mortar is slushed into the cavity below the insulation to provide the required level of protection. In addition, testing (Ref. 38 and 39) has shown that mineral wool insulation board exposed at openings in a masonry cavity wall is sufficient to pass NFPA 285 requirements. Note that mineral wool insulation cannot be exposed to the moisture in the drainage cavity. If used, it must be behind flashing or similarly protected. FIGURES 14-16 illustrate various options to protect the plastic insulation within a masonry cavity wall system.

5.3 Exterior Insulation Systems

Per the IBC, there are two compliance options for walls with foam plastic insulation on the wall exterior, such as exterior insulation and finish systems (EIFS). The first option is to protect the insulation with a 0.875 in. (22 mm) minimum thickness of cement stucco. The second option is to test the wall assembly in accordance with NFPA 268, Standard Test Method for Determining Ignitability of Exterior Wall Assemblies Using a Radiant Heat Energy Source (REF. 40) and demonstrate that the wall surface does not exhibit sustained flaming.