Advanced fire-rated glass floor systems are afoot

March 6, 2018

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Photos © Virginia Hamrick Photography/Glavé & Holmes Architecture

by Jeff Razwick
In 2001, the first recognized fire-rated glass floor system made headlines for its ability to expand glazing in a variety of building types, from increasing admissible daylight to supporting structural loads while defending against the spread of fire. (For more, read Michael Rae and Greg Butler’s “The Design and Installation of Glass Flooring and Fire-rated Glass Flooring,” a 2003 paper obtained from the Centre for Window and Cladding Technology. Visit www.bath.ac.uk/cwct/cladding_org/fdp/paper27.pdf[2].) Today, such assemblies are generating a second wave of interest for their ability to enhance performance and design goals in areas requiring a code-approved fire barrier exist between floors.

Fire-rated glass floor systems are distinguished by an ability to provide fire resistance. As defined by the 2015 International Building Code (IBC), fire resistance is, “that property of materials or their assemblies that prevents or retards the passage of excessive heat, hot gases, or flames under conditions of use.” This capability allows tested and approved fire-resistance-rated glass floor systems to satisfy codes requiring a fire barrier between floors, helping provide building occupants with a period of safe passage during a fire.

To earn a fire-resistance designation, the entire glass floor system, including the frames, glass, and component parts, must undergo and pass the fire test. During this process, the entire floor system is placed in a large furnace, loaded, and exposed to heat and flames for a given time period. The furnace’s temperature is then raised in accordance with a time-temperature curve per national standards. To pass the fire test, the system must:

Glass floor systems meeting these qualifications ensure the assembly provides both structural integrity and fire safety. Independent testing agencies, such
as Underwriters Laboratories (UL), verify these standards are upheld by evaluating and testing glass floor systems in accordance with:

Today, a small, but growing number of glass floor systems in the United States meet such standards. They are listed and classified with independent testing agencies with fire-resistance ratings up to two hours, and are available for both interior and exterior applications. Examples include lobby floors, atriums, corridors near exits, and other public egress areas at risk for fire progression.

Design teams initially specified these high-performing systems as a way to reclaim unusable daylighting space in areas requiring a fire barrier between floors. Increasingly, they are using it to push the limits of what is possible in areas with stringent fire and life safety requirements. Multiple projects found across the United States are already showcasing this type of assembly’s value. From coast to coast, the following installations demonstrate how design teams are using the multifunctional assembly to combine form and function in a powerful way.

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Designed to emulate a mullioned window, a fire-rated glass floor system at Christopher Newport University (Newport News, Virginia) fuses contemporary and classical themes.

Light well
When a private media lab in Massachusetts recognized the need for additional research space to continue pushing the bounds of innovation, it envisioned a facility where design and technology converge. The transfer of abundant daylight was central to creating the imaginative physical space. One project setback was figuring how to effectively stream natural light from the building’s skylight through the sixth floor and down into the central atrium below, while meeting two-hour fire-rated codes.

Commonly specified floor systems like concrete would meet the horizontal separation’s stringent fire and life safety codes, but block light. The material’s opaque form would prevent diffuse daylight from filtering throughout the building. The media lab’s solution was a custom, fire-rated glass floor system, referred to as the ‘light well.’

The specified fire-resistance-rated glass floor system is impact resistant, approved for loads up to 732 kg/m2 (150 psf), and fire-rated for up to two hours. During the day, it transfers diffuse sunlight from the above skylight to an atrium 10 m (35 ft) below. The atrium extends through the third, fourth, and fifth floors. It allows natural light to pass down into areas incapable of otherwise receiving sunlight from above.

The fire-rated glass floor system also incorporates a layer of protection sandwiched between two, 12-mm (0.5-in.) clear, tempered layers of glass, making the system translucent rather than transparent. The transparent interlayer provides individuals walking on the sixth floor with privacy from any occupants below. Depending on the selected interlayer or walking surface properties, the fire-rated glass floor system’s translucency can range from fully transparent to nearly opaque. Manufacturers and suppliers can provide the specifications to indicate an interlayer’s visible light transmittance, helping ensure both privacy and light transfer project goals are met.

By night, lights from the fifth-floor ceiling illuminate the floor’s translucent surface. They transform the floor into an elegant focal point, and create a sense of imagination and creativity extending into the evening hours.

An infill solution
While it is growing increasingly popular to use fire-rated glass floor systems to harness natural light in innovative ways, as evidenced in the private media lab, some design teams require the assembly to do significantly more. A case in point is the Northwestern University’s Engineering Life Sciences infill in Evanston, Illinois.

When Flad Architects was tasked with bridging two of the campus’ existing building wings to meet the need for more space, it faced the challenge of providing students with ample access to daylight. The catch was that the light needed to be balanced. Too much direct sunlight could harm specialized instruments in the nuclear magnetic resonance lab and other ground floor areas.

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Small fire-rated glass floor system segments line the perimeter of a main staircase in La Crema Estate at Saralee’s Vineyard in Windsor, California, pictured above.
Photos courtesy Technical Glass Products

The desired solution was a large, central atrium that would allow soft light to spill down and throughout the building to promote student well-being. One potential setback with drawing light through the atrium was meeting fire and life safety codes. The firm needed a code-approved floor to divide the shaft into two segments, and to provide a barrier to fire and chemicals in case of an accident.

To satisfy fire and life safety codes and help illuminate the infill, the design team used a fire-rated glass floor system.

“We needed a fire barrier in the atrium, but we did not want researchers and students to be in the dark,” said Matt Garrett, project architect at Flad Architects. “The fire-rated glass floor system allowed us to compartmentalize a very large volume of space without blocking off access to daylight.”

Keeping in mind the additional need for balanced light transfer, the firm specified the fire-resistance-rated glass floor system with ceramic-etched laminated glass. It creates a mild opacity that allows the system to diffuse daylight from above the atrium down into the nuclear magnetic resonance ground-floor lab.

“The soft, milky appearance of the fire-rated glass floor system was really important from a daylighting perspective,” explained Garrett. “Direct sunlight could damage the highly specialized instruments in the nuclear magnetic resonance lab. The pattern on the glass creates just enough opacity to allow for the transfer of soft, even light.”

Students studying on the fire-rated glass floor system can see the shape of instruments in the lab below. At the same time, the translucent glass provides privacy from ground-floor occupants looking up toward the light portal above.

“It’s great to see the students are comfortable on the fire-rated glass floor. They have no hesitation to spend time studying on it,” added Garrett.

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A ‘light well’ streams diffuse light by day, and serves as an elegant focus point by night at a media lab in Massachusetts.

A student success center’s design statement
Another project using a fire-rated glass floor system beyond conventional design standards is the Student Success Center at Christopher Newport University in Newport News, Virginia.

The original project design by Glavé & Holmes Architecture called for clear sightlines stemming from the main landing on the second floor of the student success center to the oculus 33 m (110 ft) above. However, the fire-exhaust system required in the atrium proved cost prohibitive. Forced to think beyond traditional building methods, the firm landed on a 4.5-m (15-ft) diameter fire-rated glass floor system. It acts as a code-approved fire barrier and viewing portal in a highly visible, design sensitive area—a duality crucial to the project’s success.

The fire-rated glass floor system not only provides critical defense against the spread of flames, smoke, and heat, but also sets off the building’s crowning dome. The stunning circular assembly features an outer and an inner ring with 12 glass sections. A solid inner ‘doughnut’ directs the eye through the fourth floor to the building’s distinctive dome. Transparent glass panels allow light to stream through the glass sections to the lower levels, adding depth and dimension to the optical environment. Aesthetically, the fire-rated glass floor system has been designed to emulate a mullioned window, fusing the university’s classical and contemporary design themes.

In addition to enabling views to the dome, the fire-rated glass floor system is suitable for high traffic pedestrian levels in the frequently used student center. Its textured, top-surface glass provides students and faculty with the necessary traction to walk across its surface without slipping, helping maximize usable walking space. As an added benefit, the fire-rated glass floor system incorporates switchable privacy glass on the walkable surface. With the flip of an electric switch, it becomes translucent to provide privacy during large events.

In practice
There are numerous ways design teams can employ fire-rated glass floor systems to improve light transfer, visibility, and aesthetics in horizontal separations with strict fire and life safety requirements. To use the assembly to its full potential, one should keep in mind the following considerations during the specification process.

Use surface treatments
In order to go beyond daylighting and make a powerful design statement underfoot, fire-rated glass floor systems are available with a variety of glass floor color and texturing options. One popular option is to use ceramic frits, which are melded to the glass surface, thereby creating visually engaging and bold design statements suitable for large glazed sections. For a more custom look, floors can feature one color, or even vibrant, alternating patterns. It is also possible to apply lettering, logos, and other decorative patterns in the form of decals or custom painting.

To ensure a fire-rated glass floor system’s slip-resistance is suitable to its location and has an appropriate Dynamic Coefficient of Friction (DCOF), particularly for indoor wet areas, it is important to engage the manufacturer or supplier early during the design process. They can point design firms to walking surface solutions, like anti-slip acid-etched glass, that provide a coefficient of friction, calculated in accordance with ANSI A137.1:2012 Section 9.6, Procedure for Dynamic Coefficient of Friction (DCOF).

Incorporate interlayers
In addition to surface treatments, fire-rated glass floor systems are available with various interlayers. These can further enhance the visual impact of the floor, add color, or create greater visual obscurity. For example, by varying the level of opacity, design teams can play with light, enhancing visual depth and engagement. To evaluate how various interlayers affect a fire-rated glass floor system’s light transmission, consider engaging the walking surface manufacturer or supplier. Many can provide specifications to indicate an interlayer’s visible light transmittance.

On a practical level, it is ideal to use more obscure interlayers for floors where modesty is a concern, including those where people are directly visible to individuals on lower levels.

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Students study on a fire-rated glass floor in Northwestern University’s Engineering Life Sciences building in Evanston, Illinois.
Photo courtesy Darris Harris and Technical Glass Products

Add backlighting
The benefits of fire-rated glass floor systems are not just limited to the daytime. Through strategic backlighting, films, and frits, design teams can turn these light portals into elegant design statements by night. For example, to achieve
a backlit appearance, the project team can install lights in the ceiling below the system. This allows for light transfer by day, but, at night, the glazed floor surface is illuminated.

Think geometrical
While fire-rated glass floor systems meet a complex set of performance requirements, they are not restricted to simple installation configurations. It is possible to install them in circular orientations, as well as vary the geometry of glass floor slabs. One should contact the manufacturer or supplier early during the design process to see what configurations are possible.

Varied sizes
Fire-rated glass floor systems do not have to be expansive to be effective. A popular daylighting alternative is to employ individual glass floor slabs. These small portals in corridors or gathering areas can admit light to interior spaces in a more limited manner. This was done effectively in the remodel of La Crema Estate at Saralee’s Vineyard in Windsor, California. Brayton Hughes Design Studio chose to line the perimeter of the main staircase with fire-rated glass floor system segments. The innovative configuration allows the system to draw light from the upper level down to the ground floor while providing critical fire resistance.

In general, individual glass panel sizes for modular systems are approximately 1210 mm (48 in.) by 1270 mm (50 in.). They can be used individually or together to create expansive configurations. If designs call for glass floor slabs in smaller or larger panels, one should contact the manufacturer or supplier to see what is possible.

Conclusion
More buildings with stunning glass floors are announced each year. As technology continues to evolve, a growing number will feature fire-rated glazed floor systems. In order to stay ahead of this trend and learn how to use the material to its full potential, design professionals should contact manufacturers for the latest material specifications. Correct use of fire-rated glass floor systems in structures hinges on codes, performance characteristics, aesthetic goals, and other contributing factors.

 FIRE-RATED GLASS FLOOR SYSTEM CHECKLIST
Although there are many factors to consider when it comes to fire-rated glass floor systems, the following checklist can help guide proper specification.

1. Check for adequate fire protection
Before specifying a fire-rated glass floor system, it is important to ensure a third-party testing agency, such as Underwriters Laboratories (UL), has evaluated it in accordance with ASTM E119, Standard Methods for Fire Tests of Building Construction and Materials, National Fire Protection Association (NFPA) 251, Standard Methods of Tests of Fire Resistance of Building Construction and Materials, and UL 263, Fire Tests of Building Construction and Materials. This step helps ensure the floor system provides the necessary fire safety and structural integrity.

2. Verify load requirements
While the architect or structural engineer is responsible for calculating a fire-rated glass floor system’s load requirements, it is crucial to verify the specified product could meet these predetermined standards. Where questions arise, manufacturers and suppliers can aid in providing the necessary product information.

3. Consider impact safety
Another important step is to consider a fire-rated glass floor system’s impact safety. Surface damage from heavy foot traffic or long-term wear can reduce its load-carrying capacity. As a result, when specifying fire-rated glass floor systems in lobbies, common areas, and other heavily used rooms, one should consider selecting a system that can incorporate protective treatments. Fire-rated glass floor systems with a walking surface separate from the structural layer also make it easier for glaziers to replace the individual surface panels if they are damaged.

4. Account for slip resistance
Occupational Safety and Health Administration’s (OSHA’s) minimum requirement for slip resistance is a static coefficient of friction of 0.50. Since this is a general standard, care should be taken to ensure a fire-rated glass floor system’s slip resistance is suitable to its location. For example, a fire-rated glass floor system in a study area may have different slip resistance needs than one near an entryway, where people might track water across its surface. Manufacturers or suppliers offer a variety of surface treatments to improve traction, including embossed glass, cast glass, and ceramic frit texturing Design teams can work with them to identify which solutions have a coefficient of friction that has been calculated in accordance with the requirements of ANSI A137.1:2012 Section 9.6, Procedure for Dynamic Coefficient of Friction (DCOF).

5. Consider aesthetics
Glass floor color and texturing options are available to support aesthetic goals while maintaining adequate slip resistance and daylight admission. Along with surface treatments, various interlayers can be incorporated to further enhance the visual impact of the floor, add color, or create greater visual obscurity.

Jeff Razwick is the president of Technical Glass Products, a supplier of fire-rated glass and framing systems, and other specialty architectural glazing. He writes frequently about the design and specification of glazing for institutional and commercial buildings. Razwick is a past-chair of the Glass Association of North America’s (GANA) Fire-Rated Glazing Council (FRGC). He can be contacted via e-mail at jeffr@fireglass.com[7].

Endnotes:
  1. [Image]: https://www.constructionspecifier.com/wp-content/uploads/2018/03/Opener-glass-floor.jpg
  2. www.bath.ac.uk/cwct/cladding_org/fdp/paper27.pdf: http://www.bath.ac.uk/cwct/cladding_org/fdp/paper27.pdf
  3. [Image]: https://www.constructionspecifier.com/wp-content/uploads/2018/03/Student.jpg
  4. [Image]: https://www.constructionspecifier.com/wp-content/uploads/2018/03/Winery.jpg
  5. [Image]: https://www.constructionspecifier.com/wp-content/uploads/2018/03/lab.jpg
  6. [Image]: https://www.constructionspecifier.com/wp-content/uploads/2018/03/northwestern.jpg
  7. jeffr@fireglass.com: mailto:jeffr@fireglass.com

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