'While this is very unique to Minnesota and North America, this is not the first time that ETFE has been used in a cold-weather environment by any means.' 'You won't see them sitting in the stands,' said Brendan Moore, the senior project manager of the building's enclosures for Mortenson Construction, the general contractor of the project. There's also a system of thin cables to help support the ETFE panels. With an asymmetrical design and a catch-basin gutter system around it, this roof will be far better equipped for heavy snow. The Metrodome, remember, collapsed under the weight of a 17-inch snowstorm in 2010. Light studies of the site conducted by HKS concluded that 60 per cent usage on the south side of the ship-shaped building would provide as much sunshine for the seats as if the whole top was covered with ETFE. The upper layer of foil is fritted to limit the greenhouse effect, and the air helps maintain the desired thermal performance. It's due to its physical strength but also its ability to kind of elastically respond to things,' Peck said. 'You think about that actually resisting all of the climate conditions of Minneapolis, and it's quite impressive. There are three foil layers in each panel, with low-pressurized air in between for a total width around 65 centimetres25 inches. The ETFE material is in thin foil sheetsjust a tiny fraction of an inch thick. The panels being used on US Bank Stadium average roughly three metres by 90 metres 10 feet by 300 feet, so only 75 will be needed to maximize transparency. Taylor was joined on that trip by Edward Peck, a vice-president and facade specialist for Thornton Tomasetti, the Chicago structural engineering firm for the stadium. There's Allianz Arena in Munich as well as a couple of soccer stadiums in New Zealand, where Taylor visited shortly after HKS got the Minnesota project. The Water Cube in Beijing, used for swimming at the 2008 Olympics, became the largest building to incorporate ETFE. One of the ETFE pioneers was the founder of the German company Vector Foiltec, which was selected as the manufacturer for the US Bank Stadium roof. Tested to withstand weather from hail to hurricanes, ETFE began to be used in the 1980s for structures like shopping malls, zoos and schools, primarily in Europe. ETFE was originally developed by chemical company DuPont in the early 1970s as aeronautics insulation. There are a handful of ETFE buildings around the United States, like a train station in Anaheim, an amphitheatre in Kansas City, and a water park in Wisconsin Dells, Wis., but this will be the biggest. We think the perception of sitting in a facility enjoying a game when it's either raining or snowing outside and still feeling like you're experiencing an outdoor stadium is going to be phenomenal.' 'This'll be one of those well-recognized buildings in the industry. 'The easy way out would have been a simple roof,' said Kevin Taylor, the senior vice-president at HKS Architects who's managing the project for the Dallas-based firm. The memory of the Teflon-covered Metrodome, cozy and quirky but dingy, was still fresh.

With high-definition televisions at home serving as stiff competition for ticket sales in a northern climate where sunny autumn afternoons are savoured, natural light was a high priority. The transparent roof on the south side will be complemented by five 95-foot-tall pivoting glass doors on the front of the building, letting actual fresh air in on warm days. 'Clear is the new retractable,' said Vikings executive vice-president for stadium development Lester Bagley, repeating a slogan coined as the design was revealed more than two years ago. So the Vikings entered a new era of transparency: The $1.076-billion (U.S.) US Bank Stadium will open next season, boasting the only ETFE roof on a sports facility in the United States. The retractable roof would have cost more, but the Vikings realized through researching other NFL venues that roofs are rarely retracted enough to make them worth the extra expense.

Public financial support for the project was never going to prevail unless the facility was usable year-round for a variety of events, so an open-air stadium wasn't a viable option. The space-age product, scientifically categorized as a copolymer plastic, lets in light like glass would. Sixty per cent of the colossal venue, some 248,000 square feet of it, will be covered solely by this transparent material called ETFE. Look higher for the clues to this tongue-twister, all the way up to the roof of Minnesota's new stadium. It's not one of quarterback Teddy Bridgewater's audible calls, nor is it a term for a three-wide receiver set in the Vikings offence.

Vikings stadium design