by Thom Zaremba, shareholder at Roetzel & Andress
I’m often asked questions about energy codes and fire-rated glass. First, why do the model energy codes keep changing their minimum glass requirements? Second, does fire-rated glazing need to meet energy code requirements?
Energy conservation requirements for commercial buildings are generally governed by one of two model energy codes: ASHRAE 90.1 and the International Energy Conservation Code (IECC). ASHRAE is typically used for larger, more complex commercial buildings, while the IECC is typically used for smaller, less complicated buildings. They are both minimum codes. There’s also the International Green Construction Code (IgCC), or ASHRAE 189.1. It’s “above code,” meaning it’s more stringent than a minimum code and commonly used when constructing government buildings.
With that background, why do the energy code requirements for glass keep changing? Unlike opaque walls, glass in windows and doors provides occupants with natural daylight and outside views, essential to maintaining a safe and healthy environment. However, opaque walls can be packed with insulation and wrapped for airtightness, meaning it’s pretty easy to make them more energy-efficient than windows or doors.
But never fear—low-E coatings are here! When specified with insulating glass units (IGU) of two or more lites of glass covered with microscopically thin, low-E, spectrally selective coatings within energy-efficient framing materials such as warm-edge spacers, doors and windows can join insulated opaque walls to deliver significant energy savings.
Since the advent of IGUs and low-E coatings, advances in door and window technology have saved a lot of energy. However, the glass and glazing industry is constantly improving. New high-performance glazings (vacuum insulating, electrochromic and thin triple technologies—to name a few) are regularly showing up in the marketplace.
These constantly improving technologies predictably lead to an endless stream of increases in energy performance stringencies for glass. Fortunately, glass industry representatives are busy ensuring that these changes are both technically feasible and cost-effective, meaning that the increased cost of making doors and windows more energy-efficient will be offset by reduced building energy costs over a reasonable period.
The next question: Is fire-rated glazing required to meet energy code requirements? As with many code issues, the answer is yes and no. The answer is “yes” if installed in the building’s envelope. All window and glazed door assemblies in a building envelope must comply with applicable energy codes. However, the answer is “no” if the window or door is in a wall or corridor inside the building’s envelope.
At this point, the real question is: Can glazing assemblies be made to meet both the building code’s fire-rated requirements and the energy code’s ever-increasing stringencies? The answer to this question is a resounding “yes!”—there are glazing assemblies that meet both!
While I would not presume to detail how fire-rated window manufacturers build their glazing assemblies to meet energy code requirements, one reasonably common way is to manufacture the fire-rated assembly with an attached sacrificial IGU. Together, they can meet both fire-rated and energy-conservation requirements. In a fire, the energy-saving IGU is sacrificed while the fire-rated components remain intact to protect against the passage of fire.
Do these dual-purpose assemblies cost more? Of course, they do. But climate change makes energy conservation increasingly important. Likewise, in a building fire, using fire-rated glazing assemblies to prevent vertical flames from spreading from one building to the next is important.
Don’t believe it? Just ask Mrs. O’Leary’s cow!