How Fire-Resistive Glazing Is Fulfilling Aesthetic Desires and Code Requirements

By Jordan Scott

Fire-rated glazing specification is usually code driven, but that doesn’t mean it’s without aesthetic value. With upgraded machinery and facilities, fire-rated glass manufacturers can now produce fire-resistive glass sizes larger than before. This development is allowing architects to use one- to two-hour-rated glass in a variety of applications, including butt-glazed applications.

Aesthetic Protection

“Recent innovations with fire-resistive glazing and butt-glazed systems allow designers, architects and specifiers to turn fire-rated wall assemblies into clear, transparent wall assemblies as classified in the building codes,” says Mike Miller, Pacific Northwest sales manager for Vetrotech Saint-Gobain of Auburn, Wash. “These products offer a sleek, monolithic look, allowing designers to achieve longer spans of uninterrupted glass when using fire-resistive glazing.”

Use of fire-rated transparent wall assemblies is determined by codes. Egress corridors and stair assemblies are common applications. Transparent wall systems typically are tested to ASTM E119 – 20, Standard Test Methods for Fire Tests of Building Construction and Materials, or UL 10C, Standard for Positive Pressure Fire Tests of Door Assemblies. In testing, the assemblies must remain in place for either 60 or 120 minutes depending on the rating designed for, and then it must stay in the opening after a fire hose test.

Tim Nass, vice president of sales for Safti First of Brisbane, Calif., describes glass as a vehicle. He says the technology that prevents the spread of flames, smoke and radiant energy is actually between the glass lites. Many architects prefer glass’ transparency and ability to let light into a space rather than an opaque wall for applications requiring a fire-rated product. In response to that desire, fire-rated glass manufacturers have developed large fire-resistive, butt-glazed systems without mullions or framing between the glass lites.

Nass says architects want the product to blend in with its non-rated counterparts.

“From a design standpoint they don’t want it to stand out,” he says.

This is especially important when fire-rated assemblies are included as part of the building envelope. Nass explains that, in 2015, New York City changed its building code to be more geared toward fire-resistive facilities with one- to two-hour ratings. In zero lot line applications (where two buildings share the same tax lot or are close in proximity) the aim is to prevent fire damage or spread to nearby buildings.

“Architects want to ensure there’s not a skip of the record, which would happen if the rated portion included a ton of intermediate and smaller lites. They want it to match the rest of the building,” he says.

Achieving Development

The interlayers in fire-rated glass can sometimes be activated even if there isn’t an active fire.

“Typically, in day-to-day use, you want to make sure the materials are protected and don’t respond in a way that causes the glass to trigger … You don’t want a reaction to occur so we have to make sure that if the material is put in place with exposed edges the materials don’t react,” says Devin Bowman, general manager at Technical Glass Products (TGP) of Snoqualmie, Wash.

TGP’s development team spent time making sure that when the fire-rated glass material is handled, transported and delivered to jobsites or handled and transported that it will still look like transparent glass and provide the level of life safety protection needed in the event of a fire.

Bowman adds that it’s important to make sure the conditions surrounding the system are efficient so that the glass still performs and stays in place if there’s an impact or structural shifts in the building.

“There needs to be careful analysis done on the surrounding frame conditions and the ways the system is anchored,” he says, adding that the glass is usually thicker in butt-glazed systems than fully captured systems.

Nass says fire-rated glass is a “big-ticket item,” but that there’s only so much the market can bare before project teams begin looking at other options.

“We need to meet performance, code and aesthetic requirements in a way that’s compatible with the owner’s budget,” he says.

In order for the glass to have the structural integrity necessary for butt glazing, it must be thick and robust, says Nass. He explains that it must be designed in a way that an occupant is comfortable sitting behind a one- or two-hour barrier.

Bowman adds that the way the system fits within a space matters.

“When considering fire-rated glass in butt-glazed applications, it’s also important to consider material makeup and the role it plays in creating interior spaces with virtually uninterrupted views. For example, in TGP’s Fireframes ClearView System, Pilkington Pyrostop is made from a solid multi-laminate glass with layers of Pilkington Optiwhite glass, which is a nearly colorless, wireless, low-iron float glass, separated by clear intumescent interlayers,” he says. “This make-up eliminates the need for colored internal spacers or vertical mullions between adjoining pieces of glass as called for in some alternative systems. The system also features a narrow, 5-mm vertical butt joint, both of which help maintain its seamless appearance.”

Miller says Vetrotech now offers larger sizes to help designers achieve uninterrupted spans, with butt glazing free of vertical mullions. He explains that the largest technological innovation is the butt-glazed system itself.

“What was previously required to have bulky metal framing can now be designed as a full glass assembly, without compromising code,” he says.

In addition to being able to improve the aesthetics of a fire-rated application, butt-glazed, fire-resistive systems provide many other benefits, such as daylighting. Miller says these assemblies can help design teams meet LEED criteria since they promote better light transmission and improved views.

Fire-Rated Considerations for Timber Curtainwall

Interest in timber curtainwall is growing in the U.S. as many recognize the beauty of wood. Greg Header, president of Solar Innovations in Pine Grove, Pa., says that achieving a fire-rated timber curtainwall system may mean sacrificing thermal performance and aesthetics.

Timber curtainwall can be tested to ASTM E84 – 20, Standard Test Method for Surface Burning Characteristics of Building Materials. To pass the test, a fire retardant may need to be placed on the wood.

“When you do that it can change the chemical structure or bonding, which makes the wood more susceptible to checking so you don’t get the finish or aesthetic you want,” he says, adding that there are also environmental concerns.

Header says the best way to achieve a fire rating is to have sprinklers at the opening.

“Wood curtainwall is a premium product and sprinkling is the way to go. It’s better to design a building and do the openings like that for long-term sustainability,” he says. “… It also creates an overall better building design and aesthetic. Wood curtainwall becomes a great accent and defining detail.”

Header describes timber curtainwall as being in its infancy phase in the U.S. He believes that as increased demand is driven by architects, the U.S. will start to see more codes relative to timber. However, he says the codes have to meet the reality of dealing with the product.

“As of right now, sprinkling is the best way to control fire in the building envelope,” he says. “… If you turn it into something it’s not it will lose its value and beauty.”

Jordan Scott is an assistant editor for USGlass magazine.

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