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Stadium exhibits purple (and green) pride

From the 66,200 seats in the stadium bowl to club space lighting, there’s a lot of purple in U.S. Bank Stadium. But from the early planning stages, stadium designers and planners had another color in the back of their minds: green.

In fact, the 2012 stadium legislation that authorized public funding for the $1.1 billion stadium required an “environmentally and energy efficient” design, and directed the project team to “make an effort” to achieve LEED certification or its equivalent.

The building, built by Golden Valley-based Mortenson Construction and designed by HKS of Dallas, is on track to receive some level of LEED certification, said Michele Kelm-Helgen, chair 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 stadium hosts its first official event. “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 is based on everything from efficient use of energy and water to access to mass transit.

Four existing NFL stadiums currently have LEED certification: Soldier Field (Chicago), Levi’s Stadium (San Francisco), M&T Bank Stadium (Baltimore) and Lincoln Financial Field (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 tops among NFL stadiums. (The Atlanta Falcons are aiming for LEED Platinum for their new stadium, scheduled to open in 2017.)

U.S. Bank Stadium is on track for 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 stadium’s design, boasts of the stadium’s “authentic sustainability,” which touches on everything from the hole in the ground on the project site to the stadium’s roof.

Though the 1.75 million-square-foot stadium is nearly twice as big as the Metrodome, the building it replaced on the downtown Minneapolis location, the project team says it will actually consume less energy and water.

Energy costs will be 16 percent lower compared with 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 green-building game-changer.

The ETFE roof — along with the building’s high-performance glass — brings abundant natural light into the seating bowl, and allows for a single “ridge beam” design that saves 2,000 tons of steel, with an estimated $3 million savings in structural steel costs.

“As opposed to what was here in the Metrodome — a fabric roof that was hermitically 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 elements are less obvious.

The 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 is LED.

MSFA CEO/executive director Ted Mondale said at the time that the LED light would save about $300,000 per year.

Low-flow fixtures in the restrooms will save about 5.67 million gallons of water in the inside, while native plantings and efficient irrigation systems will reduce landscape irrigation needs by 50 percent, HKS says.

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

From a site standpoint, the project gets green building points by 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: After the Metrodome was torn down to make way for the building, most of the materials were reused or recycled. And by building on that site, the project team saved about 500,000 cubic yards of excavation.

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.

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