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Executive Perspectives

EXECUTIVE PERSPECTIVE: Birds, glass, and sports stadiums

Deborah Laurel

16 Sep 2014

As we approach the centennial of The Migratory Bird Treaty Act of 1918, enacted to make it unlawful to kill America’s native birds, threats to the future of many species are on the rise. Various communities across the U.S. have reached the conclusion that the time to employ bird-friendly building design has arrived. Meanwhile, new building construction is expanding with the population, and glass buildings have become ubiquitous. A Pilkington industry report notes that 6 million tons of glass was installed in North America in 2008 alone. Birds are facing a rapidly rising wave of hazard.

As an architect, I encountered the collision problem at completion of one of our projects when the director complained that birds were crashing into the windows. I began to work with Audubon, The American Bird Conservancy, architects, and scientists to identify alternative approaches to glass that can lower the risk of a fatal collision. Interestingly, our testing has shown that visible marks on glass, covering as little as 5% of the surface, can reduce collisions by up to 95%. In addition to marking glass with a permanent pattern, such as ceramic frit, lowering glass reflectivity is equally important. Just as there are many recipes for bread, there are many recipes for requisite energy coatings on glass. Among common architectural glass products, coating reflectivity ranges from 5% to a high of 40%. In simple terms, this highly reflective glass is coated with a mist of “silvered” metal oxides resulting in 60% transparency. As an example, Minnesota Audubon’s data on the specified glass for the upcoming Minnesota Viking’s stadium indicates 30% reflectivity, an alarmingly high rating. Add to this plans to include a new park adjacent to the mirrored windows of the stadium, and the results are predictable.

As a volunteer for New York City Audubon’s Project Safe Flight I saw firsthand the destructiveness of glass installed at buildings in Manhattan. I collected migratory bird species, such as the sunflower yellow Magnolia Warbler, and other birds that had all perished by flying toward the reflection of adjacent parks in the windows of the buildings I was assigned to monitor. Project Safe Flight offers instructive data for a building similar to the stadium, the Jacob Javits Convention Center. It is a large glass curtainwall exhibit hall that opened in 1986. The reflectivity of the original glass was 35%. In three months of Project Safe Flight monitoring during the fall of 2007, 75 collision fatalities were collected. Recently, the building skin was replaced with a mix of clear and dot frit glass with a low 8% reflectivity. Fall 2013 post-construction monitoring totaled only four fatalities, a 95% reduction!

The proposed stadium for the Minnesota Vikings, designed with 200,000 square feet of monumental glass walls, is an example of the grave threat posed by a reflective glass building. It is a fatal avian collision trap. Although Minnesota Audubon has approached the Minnesota Sports Facilities Authority with information on safer glass options, the Vikings have declined to revisit the stadium design.

Viracon, a Minnesota based company, supplied the glass for Javits, and they also will provide glass for the new Vikings stadium. Our inquiries with Viracon have revealed that glass similar to the stadium selection, but with much lower reflectivity, is available at negligible increase in cost. The addition of ceramic frit may add up to 20% to the glass material cost, but this is a tiny fraction of the myriad trade costs required to build a stadium. And frit adds long term benefits including energy-saving solar shading, as well as control of glare, that is desirable in a stadium. Just as there are many types of glass, there is a wide range of pricing.

Perhaps a bird-friendly selection can be identified for less than the $1.1 million cost cited. Structural steel erection has just begun at the stadium, so it may be 9-12 months before the windows are released for fabrication. That’s enough time to change course. The Minneapolis City Council has passed a resolution asking the Vikings to add frit to the glass. The State of Minnesota has a $498 million stake in the stadium, as part of a joint venture with the Vikings. Surely a prominent State appointed institution such as the Minnesota Sports Facilities Authority can find a way to join Audubon and initiate a change of the specified stadium glass.

Across the nation, changing our approach to glass is critical to the future of America’s native birds, such as the Ruby-throated Hummingbird, a species that is on the top ten list of window collision casualties collected in Minnesota.

Glass is what we make it. It’s time to make it safer.

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