7
Fire-Resistive Construction
Fire resistance is the major factor in determining classification of construction types. Structural materials are broadly classified as combustible or noncombustible. Noncombustible materials provide greater resistance to fire by their nature. But even noncombustible structural materials can be weakened by exposure to fire. Materials that have capabilities to resist fire of a designated intensity for a length of time as determined by fire tests can be applied to structural materials to achieve required fire resistance. As we saw in the discussion of types of construction, there is a direct relationship between fire-resistance requirements by construction type to occupancy type and to the allowable number of occupants.
The code recognizes two basic methods for providing fire-resistive protection to ensure life safety in buildings. These can be classified as either passive or active protection. The differences between these approaches lie in the way they respond to the effects of fire on a building structure. Passive protection is built into the building structure and provides a barrier between the structure and the fire. Active protection such as fire sprinklers responds to fire by activation of systems to contain or suppress fire and smoke to allow the structure to remain intact for a longer period of time than without protection, thus allowing the occupants to escape. The code allows trade-offs between the provision of active versus passive fire protection. For example, the level of structural fire protection requirements may be offset by provision of fire sprinklers under certain circumstances in certain occupancies. Note that this may occur only under very limited circumstances.
In this chapter, we consider code requirements for passive fire resistance; Chapter 9 discusses active measures of fire resistance. For designers and owners, the trade-offs between passive and active fire resistance are part of the design and economic analyses that go into deciding which systems are most suitable for a given project. The consideration of passive versus active systems is part of the iterative process of comparing occupancy and site requirements to allowable heights and areas for various construction types. Again, as noted in previous chapters, design goals typically involve using the most economical construction type that meets the needs of the occupancy.
The code recognizes the efficacy of trade-offs between types of construction and types of fire protection. It also recognizes that there are limits to the value of the trade-offs between active and passive fire-resistance as they relate to types of construction and uses. Where active systems are required by the code in relationship to given criteria, such as to increase heights and areas, then the provision of active systems in lieu of passive protection is generally not allowed. The idea of a trade-off implies a voluntary selection by the designer of how to provide the required degree of fire resistance. When code provisions otherwise require active systems, they are thus not available to offset passive requirements.
Fire-Resistive Construction
Fire-Resistance Ratings
Definitions, as in other chapters, have been removed from this chapter. The texts of the definitions are contained in Chapter 2. The 2012 edition of the code moved all of the definitions, except for those of the appendices, into Chapter 2. § 202 defines fire-resistance rating as “the period of time a building element, component or assembly maintains the ability to confine a fire, continues to perform a given structural function, or both,“ as determined by tests or methods prescribed in § 703. Building Element is defined as: “A fundamental component of building construction, listed in Table 601, which may or may not be of fire-resistance-rated construction and is constructed of materials based on the building type of construction.“ The time-rating in hours indicates how long a building material, element, or assembly can maintain its structural integrity and/or heat-transfer resistance in a fire, and corresponds to the construction type designations in Chapter 6 of the code.
§ 703.2 prescribes that fire-resistance ratings be assigned on the basis of a fundamental fire test promulgated by ASTM International (formerly known as the American Society for Testing and Materials) or Underwriters Laboratories (UL). For example, ASTM Test E 119 exposes materials and assemblies to actual fire tests. UL 263 is also listed as another set of criteria. The material or assembly being tested is installed in a furnace in a condition similar to the anticipated exposure—i.e., vertical for walls, horizontal for floors or ceilings—and then exposed to a fire of a known intensity. The fire exposure is governed by a standard time-temperature curve whereby the fire grows in intensity over a given period of time, reaching a predetermined temperature at a given rate and maintaining that temperature thereafter. The sample is then exposed to the fire until failure occurs or until the maximum desired duration of protection is exceeded. This determines the fire-resistance rating in hours for the material or assembly in question.
§ 703.2.5 allows exterior bearing-wall rating requirements to equal those for nonbearing walls when all factors such as fire separations and occupancy are considered. This exception recognizes that fire resistance in exterior walls is concerned with stopping the spread of fire beyond the structure as well as protecting the structure. Since the governing criteria for this condition is preventing the spread of fire outside the building, the code recognizes that there is no point in protecting the structure to a higher level than is required for the walls enclosing the space.
§ 703.2.3 assumes that tested assemblies are not restrained under the definitions contained in ASTM E 119 or UL 263. “Restrained” refers to the ability of structural members to expand or contract under fire conditions. Assemblies considered as restrained typically have a higher hourly rating with less application of fire protection and are thus attractive to use in design. However, the code requires that such assemblies be identified on the plans. The difficulty of designing and proving that assemblies are truly restrained very often outweighs any advantages gained in reducing the quantities of fire-protection materials used. We recommend that designers follow the lead of the code section and assume all assemblies to be unrestrained when determining fire-resistance requirements.
Methods for Determining Fire Resistance
While fire ratings are fundamentally based on the ASTM E 119 or UL 263 tests to determine hourly ratings, § 703.3 allows designers to use several methods to demonstrate compliance with fire-resistive criteria. One method allows the use of ratings determined by such recognized agencies as Underwriters Laboratory or Factory Mutual. The code itself contains a “cookbook” of prescriptive assemblies in Table 721, which gives the designer a list of protection measures that can be applied to structural members, to floor and roof construction, and to walls to achieve the necessary ratings. § 722 allows the designer to calculate the fire-resistance of assemblies by combining various materials. This gives much greater flexibility to meet actual design conditions than does the very specific set of assemblies listed in Table 721.
§ 703.3 also allows engineering analysis based on ASTM E 119 or UL 263 to be used to determine projected fire resistance. This typically requires use of a consultant familiar with extrapolations from data acquired from similar fire tests to predict the performance of systems without the time and expense of performing a full-scale fire test.
§ 703.3 also acknowledges the testing measures prescribed in § 104.11, which allow the building official to approve alternate ways of meeting the code when new technologies or unusual situations are encountered. The reality of using this clause is that the building official will require testing or a consultant's verification of the efficacy of a proposed fire assembly rating in order to grant approval to alternate fire-resistance systems. The designer will need to offer convincing evidence in some form to allow the building official to determine if the proposed system is code-compliant.
Test criteria appear in § 703.4 to clarify that fire tests for rated assemblies may not include fire supression. The assemblies must pass the tests without additional coooling from fire-suppression water. This section reiterates that the requirements for passive and active protection are to be considered separately.
§ 703.5 defines noncombustibility in terms of test criteria. The characteristics that determine noncombustibility must not be affected by exposure to age, moisture, or atmospheric conditions. The code also recognizes that certain combinations of combustible and noncombustible materials may be considered as noncombustible if they meet test criteria.
Chapter 7 analyzes various construction components and conditions in light of their fire-resistance capabilities. Once again, as in other chapters, the code sections take the form of statements and exceptions. The code is organized to move from the exterior of the building to areas inside the building and then to the structure. The first set of assemblies can best be thought of as planes, both vertical and horizontal, arranged around the structural system. These planes may be bearing walls and part of the structural system, or they may be curtain walls or interior partitions independent of the structure.
Various interrelated conditions impact the fire-resistance requirements of the systems considered. Openings (and their protection), location on the property, relationships of exterior walls facing each other (as in courts), separations of interior spaces by fire walls, vertical circulation, vertical openings, protection of egress paths, smoke barriers, penetrations by utility systems, the abutment of floor systems with curtain-wall systems, and fire-resistive protection of structural systems—all must be considered. We will explore each of these sets of requirements in the same order they are presented in the code.
Per § 703.7, fire walls, fire barriers, fire partitions, smoke barriers, and smoke partitions—or any other wall that requires protected openings or penetrations—are to be identified with a permanent sign or stencil marking. The marking may be in concealed spaces when they are accessible. The markings are to occur at intervals not exceeding 30' (9144) and the lettering is to be at least 3'' (76) high and read: “FIRE AND/OR SMOKE BARRIER–PROTECT ALL OPENINGS” or similar wording. The markings are required in concealed areas where access is possible. If there is no access to a concealed space, or if there is no ceiling to form concealed spaces, then markings are not required.
Fire Resistance of Structural Members
§ 704 requires that the fire-resistance ratings of structural members and assemblies comply with the requirements for type of construction as set forth in Chapter 6 and Table 601. The ratings should be complementary in that the structure supporting a fire-resistance-rated assembly should have at least the rating of the assembly supported.
§ 704.8 prohibits inclusion of service elements such as pipes or conduits into the fire-protection covering. This recognizes that such elements can conduct heat through the fire protection to the structural member and thus potentially compromise the time rating for fire resistance.
§ 704.10 addresses the protection of structural members located on the exterior of a building. The protection of such members is set forth in Table 601 and must be as required for exterior bearing walls, for the structural frame, or as required for exterior walls based on fire separation distance per Table 602, whichever is greater.
Exterior Walls
The contents of § 705 apply more broadly than its title would suggest. The relationship to the property line of exterior walls as well as openings within and projections from the walls are covered in this section. The wall criteria also interact with the type of construction to dictate the fire resistance of the elements of the wall. This section should be read in conjunction with § 1406, which governs the use of combustible materials on the exterior face of exterior walls. Exterior egress balconies are to comply with § 1021, and exterior egress stairs are to comply with § 1027.
Projections
§ 705.2 governs the extent of allowable projections according to their relationship to the property line. The combustibility of the projections is governed by the wall construction type (which as we have seen is related to heights, areas, and occupancy types). Combustible projections extending to within 5 feet (1524) of the line used to determine the fire separation distance are to be of not less than 1-hour fire-resistance-rated construction, Type IV construction, fire-retardant-treated wood, or as required by § 1406.3.
Older IBC editions had a complicated set of standards for determining the extent of allowable projections based on how far beyond the wall the projection extended. The code now relates the extent of an allowable projection to the fire separation distance of the exterior wall at the projection location and expresses it as the minimum distance from the line used in determining the fire separation distance.
Minimum Distance of Projection per Table 705.2
Combustible Projection Protection per § 705.2.3
Balconies and Similar Projections
§ 705.2.3.1 requires balconies to meet the requirements of Table 601 for floor construction or to be of Type IV construction. The aggregate length of balconies may not exceed 50% of the building perimeter on each floor. This applies to all construction types. The exceptions again have a significant impact on how this section is applied in practice. The exceptions are:
- On buildings of Type I or II construction that are three stories or less in height, fire-retardant-treated wood may be used for elements such as balconies or exterior stairs that are not used as required exits.
- Untreated wood may be used for pickets and rails at guardrails that are under 42'' (1067) in height.
- Balconies and similar appendages on buildings of Type III, IV, or V construction may be of Type V construction. Also fire sprinklers may be substituted for fire-resistance ratings when sprinklers are extended to these areas.
Multiple Buildings on the Same Property
§ 705.3 assumes that, when determining the protection requirements for multiple buildings on the same property, an imaginary line exists between the buildings or elements. The code does not specify that the imaginary line be located midway between the elements, so the designer is free to locate the property line at any point between the elements in question as long as the wall protection requirements are met based on the distance to the assumed property line. The intent of § 705.3 is to prevent the spread of fire by radiant heating or convection. The impact of these conditions may be diminished by distance or by wall treatments, such as having openings in one wall face a solid wall on the opposite side of the assumed property line.
Where an S-2 parking garage of construction Type I or II-A is erected on the same lot as a Group R-2 building and there is no fire separation distance between these buildings, then the adjoining exterior walls between the buildings are permitted to have occupant-use openings in accordance with § 705.8. However, opening protectives in such openings shall only be required in the exterior wall of the S-2 parking garage, not in the exterior wall openings in the R-2 building, and these opening protectives in the exterior wall of the S-2 parking garage shall be not less than 1½-hour fire protection rating per § 705.3.
Fire-Resistance Ratings
§ 705.5 requires that the fire-resistance ratings for exterior walls be as prescribed by Tables 601 and 602. Based on the intent of the code to prevent the spread of fire from one property to another, when an exterior wall is located more than 10' (3048) from the property line, the fire exposure is assumed to be from the inside. When an exterior wall is located 10' (3048) or less from the property line, the exposure must be assumed to come from either inside or outside the building. This recognizes that another building may be built on the lot line on the adjacent property.
Openings
While § 705.7 contains detailed calculations (Equation 7-1) for determining the fire-resistance rating of protected openings, we will focus on the simpler calculation contained in § 705.8 and Table 705.8. These relate location on the property to the percentage of wall openings and whether the openings are protected or not. For windows in exterior walls to be protected they must comply with the opening protection requirements of § 716.
Protected Openings
Where openings are required to be “protected,” the code considers them to be protected per § 705.8.2 if fire doors, fire shutters, and fire window assemblies comply with § 716. Additional active fire-protection measures can also allow increases in the area of openings. For example, the provision of a fire-sprinkler system (adding an active fire-protection system to passive measures) is built into Table 705.8 to allow more unprotected openings in sprinklered buildings under most conditions.
Vertical Separation of Openings
§ 705.8.5 regulates the vertical relationship of openings to each other. These requirements do not apply to buildings less than three stories in height, or when fire sprinklers are provided. Again, provision of an active system allows more freedom in determining whether passive systems must also be incorporated.
Excerpt from IBC Table 705.8
Vertical Exposure
For multiple buildings on the same property, § 705.8.6 requires the protection of openings in any wall that extends above an adjacent roof. This protection can be provided in various ways: by distance, by opening protectives, or by protection of the roof framing and its supporting structure. The principle is one of reduction of the likelihood of fire spreading from one location to another. The buildings must be separated by a minimum distance, some method of fire protection applied to the openings, or the construction facing the openings must be protected.
Fire protection of openings in exterior walls other than windows and doors must be addressed as part of the design as well. Expansion and seismic joints, wall and floor intersections, ducts, louvers and similar air-transfer openings must comply with the detailed requirements of sections discussed later in this chapter.
Parapets
§ 705.11 makes a general statement that parapets shall be provided at exterior walls of buildings. The purpose of parapets is to impede the spread of fire from one building to another by providing a barrier to fire and radiant heat transfer if fire breaks through the roof membrane.
The exceptions that follow reduce or eliminate the need for parapets if any of the conditions are met. The list of exceptions becomes the code criteria, not the more general opening statement that parapets will always occur. Note that there may be extensive construction work involved to avoid a parapet. The converse is also true that the provisions noted in the exception can be avoided by providing a parapet. The exceptions, where parapets are not required, can be summarized as follows. No parapets are needed where:
- The wall satisfies the fire-separation distance criteria in accordance with Table 602.
- The building area does not exceed 1,000 sf (93 m2) on any floor.
- The roof construction is entirely non-combustible or of at least 2-hour fire-resistive construction.
- The roof framing is protected against fire exposure from the inside, as illustrated to the right.
- In residential occupancies, a fire barrier is provided by sheathing the underside of the roof framing, or the roof sheathing is of noncombustible materials for 4' (1219) back from the roof/wall intersection and the entire building has a Class C or better roof covering.
- § 705.8 allows the wall to have 25% or more of its openings unprotected due to the building's location from a property line.
Fire Walls
§ 202 defines a fire wall as a fire-resistance-rated wall whose purpose is to restrict the spread of fire. To perform this function, a fire wall must extend continuously from the building foundation to or through the roof, and have sufficient structural stability to withstand collapse if construction on either side of it collapses.
Structural Stability
§ 706.2 requires that a fire wall have a structural configuration that allows for structural collapse on either side while the wall stays in place for the time required by the fire-resistance rating. Walls constructed per the requirements of NFPA 221 will be deemed to comply with this section. Using a double wall is the clearest way to comply with the structural collapse requirements.
The interrelated requirements of seismic design and sound control must be carefully considered along with the structural stability criteria, as all of these requirements are integrated into a project. This should be discussed early in the design process with the AHJ.
Materials
§ 706.3 requires fire walls to be constructed of noncombustible materials, except in Type V construction, where they can be of fire-protected combustible construction.
Fire-Resistance Ratings
§ 706.4 bases the required fire-resistance ratings of fire walls on occupancy. For most occupancies, fire walls are required to have 3-hour fire-resistance ratings. Table 706.4 allows 2-hour ratings in Type II or V buildings for certain occupancies. Where different occupancies or groups are separated by a fire wall, the more stringent requirements for separation rating will apply.
Horizontal Continuity
§ 706.5 specifies that fire walls are to be continuous horizontally from exterior wall to exterior wall, and extend at least 18'' (457) beyond the exterior surface of the exterior walls.
Vertical Continuity
- Where a fire wall projects above a roof that slopes at more than 2:12 the fire wall is to project above a point that is 30'' (762) above a point measured 4' (1219) laterally from the top of the wall.
- No horizontal offsets in the fire wall are permitted.
The same principles for turning the fire separation construction perpendicular to the fire wall at exterior walls apply to where fire walls meet roof construction. Roof construction is to be noncombustible, of fire-retardant-treated wood, or have fire-resistive materials applied on the inside to protect the roof framing. For design purposes, it is best to presume that this fire protection of roof construction extends a minimum of 4' (1220) on each side of the fire wall when framing is parallel to the wall and the full length of the span when the framing is perpendicular to the fire wall.
Exceptions to 30'' (762) extension of fire wall above roof:
Penetrations and Joints
Openings, penetrations, and joints are required to have fire protection per sections occurring later in Chapter 7. Per § 706.11, ducts are not allowed to penetrate fire walls on property lines. Exceptions allow ducts at fire walls not located at lot lines where fire assemblies per § 717 protect the duct penetrations and the aggregate area of openings does not exceed that permitted under § 706.8.
Stepped Roofs
When a fire wall serves as the exterior wall of a building and separates buildings having different roof levels, the criteria of § 706.6.1 apply to the lower roof. This may also apply to construction of the wall for a designated height and opening protection. The lower roof allowance is one option available.
Fire Barriers
Fire barriers are similar to fire walls but with simpler criteria. They are used to separate interior exit stairways from other egress components, to separate different occupancies, or to divide a single or mixed occupancy into different fire areas. Required fire-resistance ratings for fire barriers are determined by their use. Barriers used in means of egress protection are rated per the applicable sections in Chapter 10. Occupancy separation ratings are per Table 508.4. Fire resistance ratings between fire areas are to be per Table 707.3.10.
Fire Partitions
Fire partitions are the next level of fire-resistive wall construction below fire walls and fire barriers. They typically have 1-hour fire-resistance ratings and are primarily used for separations between listed building elements.
Fire partitions have the same relationship to exterior walls as fire walls and fire barriers. They also have similar requirements for penetrations, openings, and ductwork as for the other groups of partition types.
Fire partitions are to be securely attached to one of the following:
Per § 708.4.2, in combustible construction where fire partitions do not extend to the underside of the floor or roof sheathing, deck, or slab above, the space above and along the line of the fire partition shall be provided with one of the following:
Smoke Barriers and Horizontal Assemblies
Smoke Barriers and Smoke Partitions
§ 709 and § 710 treat smoke barriers as fire barriers, but with emphasis on restricting the migration of smoke. Smoke barriers are required to have a 1-hour rating with 20-minute-rated opening protectives. Smoke partitions are required to restrict smoke movement but are not required to have a fire-resistance rating.
Openings in smoke barriers are to be protected per § 716. There are exceptions for opposite-swinging and sliding doors in I-2 occupancies.
Horizontal Assemblies
§ 711 describes the requirements for floor/ceiling assemblies and roof/ceiling assemblies that require a fire-resistance rating. Their required fire-resistance rating is determined by their use. The rating is primarily determined by the fire-resistance rating based on type of construction as dictated by Table 601. When separating occupancies or dividing a single or mixed occupancy into fire areas, the fire-resistance rating of the horizontal assembly must also be examined against the requirements of Table 508.4 and Table 707.3.10.
The criteria for penetrations of horizontal assemblies are more stringent than those for vertical assemblies, as the passage of smoke and gases vertically between floors of a building is of great concern and is facilitated by natural convective forces.
Where ducts are not required to have fire or smoke dampers complying with § 717 they are required to be treated as penetrations, and the spaces around the penetrations to be sealed per this section.
Horizontal assemblies have the same continuity requirements as for vertical assemblies. Penetrations, joints, and ducts are to be protected as for vertical assemblies; refer to § 707, § 712, and § 713.
Fire Resistance of Interior Walls
Proportional Examples of Fire-Resistance-Rated Construction at Interior Walls
Not all types of the fire-resistance barriers illustrated below apply in all occupancies. Those that do not apply in Group E or Group B occupancies are noted. The drawings are not to scale; they are for comparison and reference purposes only.
Vertical Openings
Vertical openings through floors can allow the movement of fire or smoke between floors. This represents a clear hazard to life safety that must be addressed in the design of the building. The code addresses treatments for various types of vertical openings. One of these treatments is the enclosure of openings in shafts. This is covered in § 713. Other provisions for treatment of openings are contained in § 712.
There are several items listed under § 712.1 that spell out requirements for vertical openings. The subsection numbers are as listed below:
Shaft Enclosures
The code requires that shafts not have multiple purposes. Penetrations in shaft walls are limited to those related to the purpose of the shaft. For example, ducts serving occupied spaces should not run through interior exit stairways, but ducts supplying air to the enclosure may be provided as long as penetration protection requirements are met to maintain the fire rating of the enclosure.
§ 713.13 addresses refuse and laundry chutes. The code recognizes that these shafts may interconnect many floors of a building. Requirements are included to provide a shaft, but also included are requirements to separate the chutes from the rest of the building with 1-hour-rated access rooms on each floor and 1-hour-rated termination rooms at the bottom of the shaft. Active fire protection is also required for these shafts per § 903.2.11.2.
§ 713.14 requires that elevator, dumbwaiter, and other hoistway enclosures be constructed in accordance with § 713 and Chapter 30. The requirements for elevator, dumbwaiter, and similar hoistways have been moved from §713.14 to Chapter 30, which covers elevators.
Penetrations and Joint Systems
Penetrations
§ 714 requires that penetrations be protected to maintain the fire-resistive integrity of the assembly being penetrated.
The governing criteria for penetration protection systems are that they prevent the passage of flame and hot gases into or through the assembly. Penetration treatment requirements are based on the size and quantity of penetrations. The requirements for through-penetration fire stops call for tested assemblies meeting minimum criteria for resistance to the passage of flame and hot gases. The basic criteria are that the required fire resistance of the penetrated assembly not be compromised or reduced. Certain limited penetrations by small pipes or electrical components of specified sizes are allowed by exceptions.
Penetration firestop systems are given “F” and “T” ratings. An F-rating is related to the time period that a through-penetration firestop system limits the movement of fire through a rated assembly. This rating should be nominally equal to the rating of the building assembly where the penetration is located. A T-rating applies to any penetration, not just through penetrations, and measures how long it takes to raise the temperature of an assembly by 325°F (163°C) on the opposite side of the assembly from a fire of specified size. Since the 2012 edition, the IBC also addresses “L” ratings (air leakage) for penetrations of smoke barriers.
Fire-Resistant Joint Systems
§ 715 requires expansion, seismic movement, and construction control joints to be treated in a similar manner to penetrations. The goal is that joints do not compromise the fire-resistive capabilities of the horizontal or vertical assemblies where they occur. Joints in fire-rated assemblies are to be fire-tested to match the assembly rating. Such joint assemblies are tested before and after movement to verify that the joints maintain their fire resistance after anticipated movements occur.
- § 714.6 requires that even non-rated horizontal assemblies have annular spaces filled to resist the free passage of flame and products of combustion.
- Penetrating items may connect no more than two stories if so treated.
- Noncombustible items may penetrate up to five stories if approved noncombustible sealing materials are used.
Opening Protectives
§ 716 addresses the requirements for protection of openings in fire-resistance rated walls. The openings may be either doors or glazed openings (windows). A glazed opening may occur in either a wall or within a door. It is permissible to have openings in fire-resistance rated walls, but the protection provided at the opening must provide some specified level of fire resistance so that the fire resistance of the wall is not compromised by the presence of the opening. Clearly doors are required to get into spaces, including rated exits. Also, it is often desired that vision panels occur in doors, or that windows occur in rated walls. This section provides the requirements for the various types of “opening protectives” that may be used in various circumstances.
The requirements of § 716 for the protection of openings in fire-resistive construction often allow the opening protectives to have lower ratings than those for the wall where they are located. For example, a 2-hour-rated fire wall typically requires a 1½-hour-rated opening protection assembly. Opening protectives are typically tested assemblies, so the designer can select compliant protection assemblies based on their tested performance.
Fire-rated glazing is a defined term in § 202. The definition contains two other defined terms. The first is “fire protection rating,” which is defined as “The period of time that an opening protective will maintain the ability to confine a fire….” The second term is “fire-resistance rating,” the relevant portion of which is “The period of time a building element, component or assembly maintains the ability to confine a fire….” These terms allow the use of glazing that can either be tested as an opening protective or be of more robust transparent or translucent fire-resistant materials, such as ceramics or glass block that are tested as building materials and not just as glazing.
Glazing materials are often tested and rated to a higher degree of protection than the code requires for a given situation. The code allows the use of glazing that exceeds the minimum requirements as long as the assembly meets the applicable minimum requirements as well. For example, glazing may meet the hose stream test when it is not needed, but such glazing would also need to meet the applicable time limits for fire-rated glazing.
| Marking | Marking Definition | Commentary |
| W | Meets wall assembly criteria | This will be a material, such as glass block or transparent ceramic material, that is more a transparent wall than a glass window. |
| FC | Meets floor/ceiling criteria | See § 2409.1 for requirements for glass in walkways, elevator hoistways, and elevator cars. |
| OH | Meets fire window criteria including the hose stream test | This is a window assembly that can take the force of a fire department hose stream and withstand both the hydraulic pressure from the hose and the thermal shock of water cooling after heating due to fire exposure. |
| D | Meets fire door assembly criteria | Glazing to occur at fire doors |
| H | Meets fire door assembly hose stream test | Similar to “OH,” but for fire doors |
| T | Meets 450°F temperature rise criteria for 30 minutes | Called out for certain specific instances in various parts of § 716 |
| XXX | Time in minutes of either the fire protection or fire-resistance rating of the glazing assembly | e.g., a 1-hour rating would be “60” and a 1½-hour rating would be “90.” |
Ducts and Air Transfer Openings
Ducts and air-transfer openings going through fire-rated assemblies must be treated in some way to prevent compromising the fire resistance of the assemblies that the ducts pass through. Note also that there are some duct penetration provisions in this section that apply to ducts in floor assemblies that are not fire-resistance-rated. Ducts without dampers are treated as penetrations per § 714. Where ducts must remain operational during a fire or smoke emergency—for example, in an atrium smoke-control system—they cannot have dampers. Alternate protection must be provided to maintain the integrity of fire protectives. Fire and smoke dampers must be tested and listed assemblies. Dampers must be provided with access for maintenance, testing, and resetting the assemblies when they close. These access panels must not compromise the fire rating of the fire assembly where they are located.
The fire-resistive requirements for fire and smoke dampers are based on the type of assembly penetrated. Requirements are stated in the familiar pattern of basic requirements followed by exceptions. The assembly types are organized in the same hierarchy as in other parts of this chapter.
Concealed Spaces
Fire can spread rapidly inside concealed spaces in combustible construction if the spread of fire or movement of hot gases is not restricted. § 718 sets out requirements for fire-blocking and draft-stopping. Note that these provisions apply only to concealed locations in combustible construction or in areas containing combustible construction.
The purpose of each requirement is to restrict or eliminate the spread of fire or the movement of hot gases in order to prevent the spread of fire within concealed spaces. These criteria typically apply to buildings with combustible construction, but they also apply where combustible decorative materials or flooring is installed in buildings of noncombustible construction.
Sprinklers are often a mitigation measure for draft-stopping of concealed spaces. However, note that in such circumstances the concealed spaces must usually be sprinklered as well as the occupied spaces.
Combustible construction materials are not allowed in concealed spaces in Type I or II buildings except when permitted by § 603, when Class A finish materials are used, or when combustible piping is installed in accordance with the International Mechanical and Plumbing Codes.
- Fire-blocking is the term used for the provision of materials of construction to restrict the free passage of flame through concealed spaces to other parts of a building.
- § 718.2.1 specifies the kinds of material that may be used for fire-blocking.
- Draft-stopping is the term used for the provision of materials or devices to restrict the movement of air within open spaces concealed in combustible construction, such as floor and ceiling cavities and attics. Draft-stopping in floors is to be per § 718.3 and draft-stopping in attics is to be per § 718.4.
- Draft-stopping is required to subdivide attics and other concealed roof spaces.
Plaster and Thermal- and Sound-Insulating Materials
Plaster
Plaster is accepted as a fire-resistance-rated material when applied as prescribed in § 719. Plaster assemblies must be based on tested assemblies. Plaster may be used to substitute for ½'' (12.7) of the required overall assembly thickness when applied over concrete. Minimum concrete cover of ⅜'' (9.5) at floors and 1'' (25.4) at reinforced columns must still be maintained.
Thermal- and Sound-Insulating Materials
§ 720 recognizes that thermal and acoustical insulating materials often have paper facings or contain combustible materials. When installed in concealed spaces, the materials must have a flame-spread index of not more than 25 and a smoke-developed index of not more than 450. Per an exception, cellulosic fiber loose-fill insulation with the requirements of § 720.6 are not required to meet a flame-spread index requirement but shall be required to meet a smoke-developed index of not more than 450.
Prescriptive Fire Resistances
The tables in § 721 provide a laundry list of assemblies deemed to comply with fire-resistance requirements for the times noted when installed at the thickness indicated. There are tables for various elements:
- Table 721.1(1) for Structural Elements
- Table 721.1(2) for Wall and Partition Assemblies
- Table 721.1(3) for Floor and Roof Systems
The assemblies listed are by no means an exhaustive list. The designer will often refer to other testing agencies that are acceptable to the code, such as Underwriters Laboratory or Factory Mutual, to find assemblies that meet the needs of the project. The designer must use these assemblies with care and identify where they are used in a project. Modifications to assembly designs should be done with caution as this may negate their approval and necessitate fire testing to prove their efficacy.
Structural Elements
Wall and Partition Assemblies
Floor and Roof Systems
Calculated Fire Resistances
When project conditions cannot be met using prescriptive assemblies, § 722 provides a methodology to calculate the fire-resistive performance of specific materials or combinations of materials. These calculations are developed for use in the code and meant to apply only to the section in which they are contained. They are designed to facilitate design and documentation of fire assemblies so that the designer and the building official will have reasonable assurance of the performance of the calculated assembly under actual fire conditions. The formulas are based on data for heat transfer in structural members, thermal conductance of insulating materials, conduction in materials, fire-test data of the fire resistance of various building materials; individually and in concert with each other, along with anticipated loads on assemblies in place.
The designer can use the data contained in this section to determine fire resistance for assemblies that do not fit neatly into the prescriptive, pretested categories contained in § 721.
On the following pages are several examples for both structural protection and assembly calculations to illustrate the principles at work in this section.
§ 722.2 Concrete Assemblies
Typical concrete has either siliceous or carbonate aggregate; for our example, we will assume the use of siliceous aggregate.
§ 722.5 Steel Assemblies
Fire protection for steel columns is dependent on the weight per lineal foot (W) of the column and the heated perimeter (D) of the column, which is related to the physical dimensions of the column.
Table 722.5.1(1) shows W/D ratios for typical columns. We will assume a W12 × 96 column.
§ 722.6 Wood Assemblies
These calculations may be used only for 1-hour rated assemblies. We will assume a wall located more than 10' (3048) from the property line. Thus the fire side is presumed to be on the interior of the building, per § 722.6.2.3.
