U.S. Bank Stadium goes for the green

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From the 66,200 seats in the new U.S. Bank stadium’s bowl to the lighting in the nearby club space, there’s a lot of purple to be seen in Minnesota Viking’s new home.

Yet the project designers always had another color at the back of their minds: green.

In fact, the 2012 stadium legislation that authorized public financing for the $1.1 billion stadium required an “en

vironmentally and energy efficient” design, and directed the project team to “make an effort” to achieve LEED certification or its equivalent.

The stadium, built by Golden Valley-based Mortenson Construction and designed by HKS of Dallas, is well on its way to receiving some level of LEED certification, said Michele Kelm-Helgen, chairwoman of the Minnesota Sports Facilities Authority.

“This was one of the things that the state and the city had highlighted as being important,” Kelm-Helgen said in an interview Monday, just two days before the first official event is to take place in the stadium. “We really focused on it from day one.”

LEED plaques are still somewhat hard to find on NFL stadium walls, but they’re becoming more common. LEED certification takes into account everything from whether a project makes efficient use of energy and water to whether it provides access to mass transit.

Four existing NFL stadiums now have LEED certifications: Soldier Field, in Chicago; Levi’s Stadium, in San Francisco; M&T Bank Stadium, in Baltimore; and Lincoln Financial Field, in Philadelphia, said Sheri Brezinka, executive director of the U.S. Green Building Council’s Minnesota chapter.

Levi’s Stadium achieved “LEED Gold,” the U.S. Green Building Council’s second-highest level of certification and the top ranking among NFL stadiums. (The Atlanta Falcons are aiming for LEED Platinum for their new stadium, which is scheduled to open in 2017.)

U.S. Bank Stadium is meanwhile on its way to receiving LEED Certified, the most basic level, Brezinka said.

“You could not say it’s the greenest, with a few other stadiums coming in with higher certifications,” Brezinka said. “But you could say it’s definitely in the top echelon of green stadiums across the country.”

A report from Dallas-based HKS, which led the design team for the stadium, boasted of the structure’s “authentic sustainability.”

Although the 1.75 million-square-foot U.S. Bank stadium is nearly twice as big as the Metrodome – the structure it replaced, the project team says it will actually use less energy and water than its predecessor.

The energy costs will be 16 percent lower than those incurred at the Metrodome, according to the HKS report. It will also use less artificial light (37 percent), indoor water (37 percent) and outdoor water for irrigation (50 percent).

John Hutchings, HKS principal and senior vice president, singled out the stadium’s semi-transparent ETFE roof as a particularly remarkable feature.

The ETFE roof — along with the building’s high-performance glass — brings abundant natural light into the seating bowl. It also allowed for a single “ridge beam” design that prevented the need for an additional 2,000 tons of steel. The estimated savings on structural steel came to $3 million.

“As opposed to what was here in the Metrodome — a fabric roof that was hermetically sealed — you can see blue sky and white clouds and a lot of daylight, which reduces our lighting load,” Hutchings said during a recent stadium tour.

Some of the other green features are less obvious.

The stadium’s mechanical systems, for example, are highly efficient, as is the building’s LED lighting. In December 2014, the Vikings agreed to pay an extra $1.249 million to ensure that the 1.7 million watts of sports lighting needed at the stadium came from LEDs.

Ted Mondale, chief executive and executive director of the Minnesota Sports Facilities Authority, said at the time that the use of LED light would result in about $300,000 worth of savings a year.

Low-flow fixtures in the restrooms will save about 5.67 million gallons of water in the inside, while native plants and efficient irrigation systems will reduce the need to use water for landscaping by 50 percent, HKS says.

A system of “vertical air risers” will meanwhile recirculate air from the upper reaches of the building to the stadium bowl to help keep fans comfortable in the winter.

As for its site, the project gets green-building points for being close to public transportation. Eventually, more than one-third of the people who attend the games are expected to use mass transit, “which is a very sustainable approach,” Hutchings said.

Another plus: When the Metrodome was torn down to make way for the new stadium, most of the materials recovered from the demolition were reused or recycled. By building on the same site, the project team avoided the need to excavate an additional 500,000 cubic yards.

About 80,000 tons of concrete, 4,500 tons of steel, and 300 tons of roof cable from the old stadium were recycled, Kelm-Helgen said.

“It was important to us not to have all that go into the landfills,” she said.