page_title: Hubert H. Humphrey Metrodome
section_title: Roof
hierarchical_section_title: Hubert H. Humphrey Metrodome / Features / Roof
caption_attribution_description: inside of Metrodome roof used after 2010.
context_page_description: The Hubert H. Humphrey Metrodome was a domed sports stadium located in downtown Minneapolis, Minnesota. It opened in 1982 as a replacement for Metropolitan Stadium, the former home of the National Football League's Minnesota Vikings and Major League Baseball's Minnesota Twins, and Memorial Stadium, the former home of the Minnesota Golden Gophers football team.
  The Metrodome was the home of the Vikings from 1982 to 2013, the Twins from 1982 to 2009, the National Basketball Association's Minnesota Timberwolves in their 1989–90 inaugural season, the Golden Gophers football team until 2008 and the occasional home of the Golden Gophers baseball team from 1985 to 2010 and their full-time home in 2012. It was also the home of the Minnesota Strikers of the North American Soccer League in 1984. On January 18, 2014, the Metrodome roof was deflated, signaling the beginning of demolition work. The Vikings played at the University of Minnesota's TCF Bank Stadium for the 2014 and 2015 NFL seasons, ahead of the planned opening of U.S. Bank Stadium in 2016.
context_section_description: The Metrodome's air-supported roof was designed by the inventor of air-supported structures, David H. Geiger, through his New York-based Geiger Berger Associates, and manufactured and installed by Birdair Structures. An air-supported structure supported by positive air pressure, it required 250,000 ft³/min (120 m³/s) of air to keep it inflated. The air pressure was supplied by twenty 90 hp (67 kW) fans. The roof was made of two layers: the outer layers were Teflon-coated fiberglass and the inner was a proprietary acoustical fabric. By design, the dead air space between the layers insulated the roof; in winter, warm air was blown into the space between layers to help melt snow that had accumulated on top. At the time it was built, the 10 acres (4.0 ha) of fabric made the roof the largest expanse ever done in that manner. The outside Teflon membrane was 1/32 of an inch thick and the inner liner of woven fiberglass was 1/64 of an inch thick. The entire roof weighed roughly 580,000 pounds (260,000 kg). It reached 195 ft (59 m), or about 16 stories, at its highest point.
  To prevent roof tears like those that occurred in its first years of service, the Metropolitan Sports Facilities Commission adopted a twofold strategy: When snow accumulation was expected, hot air was pumped into the space between the roof's two layers. Workers also climbed on the roof and used steam and high-powered hot-water hoses to melt snow. In addition, before the storm that caused the December 2010 collapse, the inside of the stadium was heated to nearly 80 °F (26.7 °C).
  To maintain the differential air pressure, spectators usually entered and left the seating and concourse areas through revolving doors, since the use of regular doors without an airlock would have caused significant loss of air pressure. The double-walled construction allowed warmed air to circulate beneath the top of the dome, melting accumulated snow. A sophisticated environmental control center in the lower part of the stadium was manned to monitor weather and make adjustments in air distribution to maintain the roof.
  Because it was unusually low to the playing field, the air-inflated dome occasionally figured into game action during baseball games. Major League Baseball had specific ground rules for the Metrodome. Any ball which struck the Dome roof, or objects hanging from it, remained in play; if it landed in foul territory it became a foul ball, if it landed in fair territory it became a fair ball. Any ball which became caught in the roof over fair ground was a ground rule double. That has only happened three times in its history – Dave Kingman for the Oakland Athletics on May 4, 1984, University of Minnesota Gophers player George Behr and Corey Koskie in 2004. The speakers, being closer to the playing surface, were hit more frequently, especially the speakers in foul ground near the infield, which were typically hit several times a season, which posed an extra challenge to infielders trying to catch them. However, beginning with the 2005 season, the ground rules for Twins games were changed such that any batted ball that struck a speaker in foul territory would automatically be called a foul ball, regardless of whether or not it was caught.
  The dome's roof color made it close to impossible to catch balls without taking the eye off the ball. As a result, fielders frequently lost balls in the roof. An example of this is seen in a home run derby put on by a softball entertainment crew prior to a Twins game. Taken at field level, the balls generally tended to be lost in the roof.
caption: Metrodome roof (2011–2013)
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