Opening the Door to Fire-Rated Enclosures

To view the figures and tables associated with this article, please refer to the flipbook above.

Building codes require all commercial buildings to defend occupants and means of egress routes in the event of a fire. The specifics for these requirements depend on several factors, from the building’s full height and proximity to other buildings to the location and construction of individual elements within the building itself. While traditionally out of the scope of structural engineering, analyzing and designing a building for fire safety is increasingly interconnected with structural systems. For example, due to lot line restrictions and brand alignment, an Audi dealership in Birmingham, Michigan, needed a fire-rated exterior curtain wall. This assembly was anchored to multiple structural points on the floor and ceiling. With the added weight of fire-resistance-rated glazing, the full assembly needed additional structural analysis to ensure the anchoring and spans were within tolerances for appropriate structural loads. Further, for larger curtain walls, secondary supports might need to be spliced into the assembly. Inside a building, fire walls, fire barriers, and fire partitions all have different structural needs, which may necessitate the analysis of a structural engineer.

This interconnectedness of structural and non-structural components and the varying degrees of structural bearing fire-rated systems can provide means, as Dr. Frederick W. Mowrer writes in an article from the January 2018 issue of STRUCTURE, “it is useful for [structural engineers] to have at least a basic understanding of building fire safety issues.”

Connected to and influenced by structural components as well as integral to a means of egress system, enclosures for stairways and elevators must achieve code-driven, fire-rated standards. These code-compliant systems do not just contribute to certificate of occupancy; they also meet a baseline of occupant safety. When structural engineers can contribute to both structural efficacy and occupant safety when designing and analyzing these enclosures, they can deliver more value to the full project team and streamline planning phases. That said, there are many options for code-compliant fire-rated enclosures.

In the past, building professionals may have been limited to opaque materials which made designing these parts of the built environment purely functional. With the advent of fire-rated glazing, the potential in stairway and elevator enclosure design saw significant expansion to its ability to support occupants with daylight, visual connection, and intuitive wayfinding. However, more design choices for these parts of a means of egress system lead to more opportunities to unintentionally specify a non-code-compliant system.

When determining fire-rated requirements for enclosures, start by analyzing the building’s broader context before drilling down into wall and opening specifications, as each component’s rating is contingent on its surroundings. Offering a basic overview of fire-rated requirements for various elements of the built environment, this article will use the 2024 edition of the International Building Code (IBC) for discussing rating requirements, but project teams are encouraged to consult local codes and contact an Authority Having Jurisdiction (AHJ) to clarify any ambiguities or amendments.

When determining the code-driven requirements for enclosures, consider the full building’s context first. For instance, if a building is located within a certain code-defined distance (usually 10 feet or less) from the lot line or other buildings on the same lot, its exterior walls and openings will need to be fire-rated. This requirement is to mitigate instances in which fires spread from one building to the next.

In addition to location, the height of a building, and subsequently the number of stories its shaft enclosures connect, plays a role in determining fire-rated design requirements. According to Section 713.4 of the 2024 edition of the IBC, shaft enclosures connecting four or more stories will need their walls and barriers to achieve a fire-resistance rating of not less than 2 hours. Enclosures connecting less than four will need a minimum of 1-hour fire-resistance ratings. The discrepancies between ratings allow more time for evacuation in taller buildings and compartmentalize a fire on its floor of origin.

While this section includes an exception for applications of reduced fire-resistance ratings under certain conditions, this exception is for high-rise building enclosures “other than interior exit stairway and elevator hoistway enclosures” (IBC Section 403.2.1.2). With exemptions and code-allowed alternatives, it is encouraged to consult with an AHJ to assess the applicability of a proposed alternative and fully understand the life safety outcomes of such a tradeoff.
With these distinctions in mind, project teams can turn toward the individual elements of enclosures.

Although IBC Section 713.4 seems to make determining the fire-resistance-rating requirements for enclosures straightforward, building teams need to account for other considerations, specifically whether a wall is a fire wall, fire barrier, or fire partition. These distinctions can impact the rating requirements for enclosures. All three fire-resistance-rated assemblies are designed to restrict the spread of fire and may include opening protectives.

The main distinction between these three elements is where they terminate. Often used to separate spaces within the same space, fire partitions terminate at the floor and ceiling. They are primarily used for corridor walls and tenant separations. As such, a fire partition likely would not be part of an enclosure.

Fire barriers are more robust and must extend from the floor to the fire-resistance-rated floor-ceiling assembly (or roof) above it. These barriers may serve as walls for entering a stairway enclosure and are subject to the rating requirements listed in IBC Sections 713 (shaft enclosures), 711 (horizontal assemblies), or 707 (fire barriers) or all three.

Fire walls are the most stringently rated of the three; they are designed for structural stability, so they remain standing even if the structure on one side collapses. These walls extend the full height of a building (foundation through the roof) and require a rating in accordance with their occupancy as outlined in IBC Table 706.4, Fire Wall Fire-Resistance Ratings.

Specifically for elevator and stairway enclosures, determining if an opening is in a fire barrier or a fire wall will impact its rating and the ratings for any opening protective within the wall in question.

First, opening protectives, whether they are doors, windows, or otherwise, will need a rating that is appropriate within their barrier or wall. IBC Table 716.1(2), Opening Fire Protection Assemblies, Ratings and Markings, details the exact requirements for door assemblies given the required wall assembly rating in hours. According to this table, most door and window assemblies will need to have fire-resistance ratings equal to their wall assemblies’ ratings. There are a few variations:

If an enclosure includes an exterior wall that is rated for two or three hours, its openings will likely need to be fire-rated for 90 minutes. For 1-hour rated exterior walls, openings will need a 45-minutes rating. Doors, sidelites, transoms, and vision panels in enclosures with 2-hour fire-rated interior walls can meet code-driven requirements with fire ratings of 90 minutes. For both exceptions, the rationale is that door and window assemblies will be free of obstruction (like boxes and furniture), which is considered fuel, so these assemblies will be less likely to experience the most intense heat and flame conditions in a building fire.

This means, for tall buildings with connected egress stairways and elevator shafts, most opening protectives will need to achieve a 90-minute fire rating. Though rare for enclosures, 4-hour rated walls only require 3-hour fire-resistance-rated doors, but its sidelight or transom assembly will need a 4-hour rating.

When glass is incorporated into these openings as vision lites, sidelites, and transoms, they should be tested and rated in accordance with ASTM International’s standard ASTM E119 or UL Solutions’ standard UL 263 for fire-resistance. For full-lite fire doors, the National Fire Protection Association’s standard NFPA 252 is required. Further, for door assemblies that must also meet temperature-rise requirements, NFPA 252 adds a stipulation that, for the first 30 minutes of the fire test, the non-fire side of the door must limit the ambient temperature to no more than 250F, 450F or 650F—with 250F allowing the least amount of heat transfer. For openings that are fire-protection-rated, NFPA 257 and UL 9, UL 10B or UL 10C are the standards listed in the IBC for determining fire-protection ratings.

The IBC has a standard fire label that abbreviates which tests a glazing assembly have passed and which application uses are appropriate for the assembly.

For ASTM E119 or UL 263:

For NFPA 257 or UL 9:

For NFPA 252 or UL 10B and UL 10c:

Numbers after the letters indicate the time in minutes an assembly can provide fire resistance or fire protection.

As an example, if a glazing assembly has “D-H-T-120 OH-120 W-120” on its label, it can be used as a 120-minute fire-resistance-rated door, window or wall, has passed the hose stream test and meets temperature-rise criteria.

Size limits often apply to fire-protection-rated glazing. For instance, fire-protection-rated vision panels are usually limited to 100 square inches. For windows and other openings with this rating, the width is limited to 25 percent of the wall’s length and shall not exceed 156 square feet, according to IBC Sections 706.8 and 707.6. This is not the case for fire-resistance-rated glazing, which is treated similarly to fire barrier material. As such, fire-resistance-rated glazing can span full walls and be incorporated into full-lite fire doors.

Enclosures can be integral to creating safe and accessible commercial buildings—whether they are of average height or are true skyscrapers. In the past, to make these elements of the built environment code-compliant, project teams were often limited to opaque materials that visually cordoned off these spaces from the rest of the building.

However, advanced, fire-rated glazing assemblies now allow a wider variety of design choices for enclosures. These glazing systems allow teams to create full-lite glass doors, long stretches of floor-to-ceiling glass wall panels, large sidelights and transoms and so much more. With the added transparency, occupants can more intuitively navigate buildings, access daylight, and feel more connected to their surroundings—all without compromising their safety in the event of a fire.

Knowing the code-driven requirements for these materials can help teams more readily push the envelope on enclosure design. ■

About the Author

Devin Bowman is General Manager of Technical Glass Products (TGP) and AD Systems. With over 20 years of industry experience, Bowman is actively involved in advancing fire- and life-safety codes and sits on the Glazing Industry Code Committee (GICC). (Devin.Bowman@allegion.com)