With football season kicking off, new features in NFL and collegiate stadiums will be top of mind for owners, athletes, and fans across the country. Stadium roof trends have varied over the years with the goal of creating stunning destinations and elevating the fan experience.
Compared to the sleek, artistic designs of today’s sports facility construction projects, the Hubert H. Humphrey Metrodome in Minneapolis, Minnesota seems basic. But, back in 1981, the air-supported roof, made of Teflon-coated fiberglass and held up by a cable net structure, was considered an innovative design.
“The Metrodome was ingenious for its time,” says Erik. “Inflatable roofs like the dome were popular in places like Texas and Florida to give fans a climate-controlled environment. The design eventually went to the wayside because the material is opaque and did not allow light to filter inside the structure.”
With NFL games traditionally being played outside, owners began requesting fully enclosed stadiums that provided an open-air feel. In the late 90s and early 2000s, the design solution was operable roofs that retracted to let in fresh air and sunlight.
NFL Stadium Trends of the Past: Operable Roof Elements That Bring the Outdoors In
NRG Stadium, home of the Houston Texans, was completed in 2002 and was the first NFL stadium built with a retractable roof. Two large sliding panels constructed of steel and translucent fabric span 180,000 square feet and open to expose the entire field.
AT&T Stadium, home of the Dallas Cowboys, features a single-span roof with two transparent, operable panels measuring 65,000 square feet total. The design also incorporated end zone platforms with operable doors to bring more of the outside in.
The roof of Mercedes-Benz Stadium, home to the Atlanta Falcons and the Atlanta United FC, features eight petal-shaped panels that open to fill the field with a large circle of natural light. The idea behind this design was to mimic the feeling of standing under the oculus of the Pantheon.
Though impressive both architecturally and aesthetically, operable roofs are not frequently opened. In fact, NRG Stadium made headlines when it opened its retractable roof for the first time six years after opening. Retractable roofs are also expensive to build and maintain and create significant design and construction challenges.
Given their minimal return on investment, owners stopped requesting retractable roof panels, leading architects and stadium contractors to seek alternatives that provided owners with the indoor/outdoor feel fans desire.
Current NFL Stadium Roof Trends: A Better Alternative to Retractable Elements
Long before the trend hit the U.S., stadium contractors in Europe and East Asia were designing roofs with translucent EFTE (Ethylene tetrafluoroethylene) panels. ETFE is a highly durable, lightweight alternative to glass that provides enough light transmission to create an open-air feel while providing the coverage needed to keep out rain and snow.
“ETFE panels are a more economical way to design a long-span roof system because of the material weight and structural requirements,” explains Dan Wacker, director of preconstruction at Mortenson. “Mechanized roof components require a lot of steel, which adds weight and cost. Temporary bracing and supports to erect the system add time and cost to construction. On top of that, the installation—and later maintenance—of the motors that operate the retracting components add up to a very expensive system.”
The aesthetic appeal of ETFE, paired with its technical benefits and cost savings over using operable panels, quickly made this material the new “retractable” in NFL stadium roof designs.
U.S. Bank Stadium, home of the Minnesota Vikings, was the first NFL stadium to utilize ETFE panels. Half of the stadium features a conventional roof with a steel frame, metal deck, and a non-transparent TPO (Thermoplastic Polyolefin) roofing membrane. The other half consists of a steel structure with panels of translucent ETFE pillows that let enough light in to sometimes require sunglasses inside the stadium.
Due to the long Minnesota winters with plenty of snow accumulation, the ETFE pillows were designed to partially deflate under the weight of snow. Compressors located high in the catwalk kick in to reinflate the pillows as the snow melts. The feature added significant cost to the design, but as this stadium was designed for year-round use, there were ROI considerations and risk mitigation that came with eliminating the inconvenience, repair expense, and lost revenue associated with a roof collapse.
Designing for the Location and Climate
“There is no one-size-fits-all answer when it comes to stadium design,” states Dan. “The design elements used in each sports stadium project are specific to the climate, location, and how they plan to use the venue.”
Allegiant Stadium, home of the Las Vegas Raiders, features ETFE panels spanning the center of the stadium roof. The stadium’s initial design called for fully transparent panels like U.S. Bank, but a few twists developed through design evolution.
When Raiders owner Mark Davis attended Super Bowl LII at U.S. Bank Stadium, he determined the sunny environment would be “too bright” for his fans. Additionally, using fully transparent panels in a hot desert climate would not comply with energy code requirements or keep fans cool during games.
The solution for Allegiant Stadium’s roof was fritting, a process that involves printing a pattern under the top layer of each ETFE pillow. The silver frit patterns reflect heat and light and can be printed to provide as high as 95% opacity.
It All Comes Down to the Complexity and Cost
Though EFTE panels are less costly than retractable panels, long-span steel systems remain one of the most expensive elements of a stadium design. To alleviate this cost, Allegiant Stadium utilized a cable net roof instead of a steel long-span system. The heavier the roof, the more structural support is needed, which results in a larger footprint, foundation, and structure, and added cost. Cable net systems are significantly lighter, requiring less structural support and therefore, less steel.
“The complexity of modern stadium roofs requires significant planning to get things right,” says Dave Mansell, field operations manager at Mortenson. “Construction partners need to get involved early in the design and planning phases of the project to help owners develop the most efficient and cost-effective structural strategies for their stadium.”
What’s Next in NFL Stadium Roof Designs?
While ETFE is a current trend in NFL stadiums, it begs to question: “What's next?” An owner's vision and a designer's creativity will continue to evolve to meet project demands. New lightweight materials are being invented and tested every day, as are materials that are stronger, more economical, and more dynamic.
Stadium roofs of the future could very much utilize electrochromic (shade/color changing) technology—one day the roof is blacked out for a big concert, then with the flip of a switch, the roof turns transparent to let the sun through for noon kickoff the next day.
Advancements in video technology have also sparked conversations about how roofs become an integral part of the visual experience, where components like an LED media mesh become an integral component of the roofing material itself. While we can't quite predict the future, what is certain is that the demand for new or renovated stadiums is at an all-time high. And there is no question that we will continue evolving as a sports design and construction community.
Building Stadiums Efficiently and Economically
Architects want to design the most iconic, unique, and memorable stadium possible. Team owners want to see their vision materialize into an innovative venue that attracts fans, creates a home field advantage, and maximizes revenue, all without breaking the bank. Achieving these objectives requires having a construction partner that knows the industry and has the expertise to find the most economical solutions for a stadium design.
“You can pretty much draw anything you want,” says Dan. “turning that vision into a reality requires collaborating with an experienced builder that provides guidance early in the design phase. Using our extensive sports construction expertise and in-depth data analysis, Mortenson helps owners and architects complete projects for the lowest total cost while maintaining the owner’s vision.”
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