AUTHENTICALLY SUSTAINABLE U.S. BANK STADIUM

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1 AUTHENTICALLY SUSTAINABLE U.S. BANK STADIUM

2 AUTHENTIC SUSTAINABILITY DESIGNING FOR THE LEGENDARY MINNESOTA CLIMATE In 2012, HKS was commissioned to build a new home for the storied Minnesota Vikings. One of the earliest and clearest goals for the project was to redefine the notion of a sustainable stadium a unique building type that looked beyond the conventional ratings and standards to focus not on what made sense for commercial offices but what made sense for the stadium. Our approach to the form was to reflect the specific location and climate of its site. It is an old way of thinking from times when buildings had to be responsive to the environment, or they would not last or be comfortable to inhabit; this is true sustainability. The result is an iconic, sculptural shape on the Minneapolis skyline that evokes ice flows colliding together on a frozen lake, or the jagged geology that once defined the treacherous cataract of nearby St. Anthony Falls, but whose shape is grounded in practical, functional considerations.

3 FORM SOUTHERN EXPOSURE SNOW CATCHMENT BASIN SNOW SHED SNOW SHED DOWNTOWN 01 If we used a typical shallow sloped or domed roof, a huge premium would have been added to the structure of the stadium due to the snow loading requirements of Minnesota. 02 Creating a steep sloped roof forms a modern-day equivalent of indigenous structures built in northern climates and allows for snow to be efficiently shed from the roof. 03 The ridgeline is modified into an asymmetrical shape, allowing for a steeper slope on the northern face of the roof and a greater surface area with southern exposure. 04 Further adjustment of the ridgeline to maximize southern exposure for increased snow melting capability of the roof 05 Cantilevers create back-span for the ridge truss, resulting in optimal structural efficiency. The cantilevers also identify major entries into the stadium from the east and west. 06 The final form of the roof allows for snow storage at the perimeter in the most efficient structural location. This also allows for free pedestrian movement around the stadium in the winter months with minimal maintenance.

4 50 PERCENT FEWER RIDGE BEAMS Typical stadium roof framing distributes loads among two or more primary trusses. Learning from traditional Nordic roof structure, designers were able to focus the roof s weight on a single and distinctive ridge beam. The use of ETFE saved us from using 2,000 tons of steel. Using ETFE on the south roof reduced snow loads by 30 percent and yielded a reduction in the roof steel tonnage by an approximate 2,000 tons equating to a $3 million structural steel savings. OPEN TO THE SOUTH Maximizing the span of the queen post trusses allows for an overall reduction in the primary roof structures. Lofting the south roof to a 14-degree slope and maximizing the roof s southern exposure for greater snow melting ability reduced the normal heavy snow loads by an estimated 25 to 30 percent, which enabled the design team to provide a relatively lightweight, long-span steel roof design. STRUCTURE The innovative structural approach allows for one of the lightest hard-roof structures on a major U.S. stadium, in a climate with the heaviest loading requirements.

5 SITE RESPONSE Utilized public transportation with increased stops. The stadium serves as a central stop between the two main light rail lines serving the Minneapolis-St. Paul International Airport and the city of St. Paul. Incorporated additional community spaces surrounding the stadium that can be used year-round. Added 36,986 square feet of green space, equal to 20 community playgrounds. Connected to downtown via 8.5 miles of indoor skyway system, it is one of the most urban stadiums in the country. Located bike racks all around the stadium to further promote bikefriendly trails and lanes located within the community. Reduced indoor water usage by 37 percent due to low-flow technology, which equals 5.67 million gallons of water a year. Reduced landscape irrigation by 50 percent with water-efficient irrigation systems and native plantings. Urban Infill: Reused the old Metrodome site, creating a viable example of urban renewal. The U.S. Bank Stadium served as a catalyst, spurring the construction of 1.2 million square feet of office space, 28,000 square feet of retail, approximately 400 residential units and a 4.2-acre green space. The reuse of the site saved approximately 500,000 cubic yards of excavation.

6 ETFE MATERIALITY Ethylene tetrafluoroethylene (ETFE) allows solar thermal heating and natural daylighting, reducing demand for artificial lighting and structural load. The ETFE also makes visitors feel as if they are sitting outside without being exposed to the elements. It is the first building in the United States to use ETFE at this scale. Reduced the roof structural steel demand by 2,000 tons with the incorporation of ETFE, high-strength steel and a sloped roof. GLASS High-performance glass promotes connection to the outdoors and minimizes the need for artificial lighting. ZINC Zinc was used on the exterior skin because it is a natural primary material that can be recycled indefinitely which benefits all players in the chain. Zinc is not sensitive to corrosion; it protects itself by developing a patina that gives it an exceptionally long life span (50 years in an aggressive urban environment to 100 years in a protected rural environment). It requires no maintenance. Zinc continues to develop protective layers throughout its life and will self-repair imperfections and scratches, greatly reducing life-cycle costs associated with the exterior of the stadium. Diverted approximately 90 percent of demolition and construction waste from entering local landfills. These materials will be recycled. The demolished concrete is used as backfill for the surrounding area. Incorporated materials with a recycled content value exceeding 20 percent. Incorporated low-voc (volatile organic compound) materials throughout the interior of the stadium.

7 HEATING The entire south face of the roof is covered in a clear roofing material called ETFE. This allows heat from solar radiation to enter the seating bowl. HEAT RESERVOIR Light coming through the ETFE roof substantially reduces the need for daytime artificial lighting and offers the psychological benefits of natural daylight. The building contains a system of vertical air risers that in winter draw warm air from the heat resevoir above and distribute it throughout the stadium and seating bowl. ANNUAL ENERGY USAGE METRODOME 104 kbtu/sf Reduced energy cost by 16 percent by way of heat recovery, air handling units, ventilation and high-efficiency motors. Reduced lighting by 37 percent due to installation of LED sports lighting. U.S. BANK STADIUM 92 kbtu/sf The majority of Vikings games are played with temperatures well under 45 degrees Fahrenheit, with temperatures sometimes plunging below minus 10 degrees Fahrenheit. Heating typically comprises up to 50 percent of building energy use in this region, and for the stadium s designers, managing these costs was job number one. The approach was to use a combination of solar heating and capturing the stadium s heat as it rises, recirculating to patrons below. The form of the building allows air to circulate and move through the stadium in both winter and summer months in a way that is fundamentally new to this building type but closely connected to the way buildings were built in this climate traditionally.

8 COOLING HEAT RESERVOIR Heat rises and is ventilated at the upper level of the bowl. In addition to allowing the hot air to escape, this chimney effect helps to drive convection currents and pull cooler outside air from below. Cool air falls across the surface of the seating bowl, cooling patrons and avoiding cooling the unoccupied central volume of the stadium. As cooler air settles at the field level, it is recirculated to the top of the seating bowl to achieve uniform cooling. With a 365-day calendar of events, U.S. Bank Stadium must be comfortable year-round. While not as intense as its winters, Minnesota summer temperatures can frequently reach into the 90s. Cooling comfort is maintained in two primary ways. By reversing the flow of the air risers, cool air is delivered from the top of the seating bowl and cascades down over seated patrons. Heat that comes through the clear roof rises to the collector reservoir and in summer is ventilated out of the peak to the exterior, which promotes air movement and keeps the interior cool.

9 OPERATIONS IMPLEMENTED a green cleaning program to prevent use of chemicals that are potentially hazardous to employees and fans. The program addresses products and materials used for cleaning, soaps for hand hygiene, equipment with reduced sound levels, and strategies for containing and cleaning of hazardous spills. INSTITUTED a comprehensive recycling program to reduce the amount of waste hauled to the landfill after an event. Commingled recycling will be utilized to maximize recycling of paper products, plastics, glass and metals. Recycling bins will be located along the concourses and outside the stadium. INITIATED a green education program that will be an informative component of stadium tours. Visitors will learn about the strategies implemented in the stadium to reduce energy and water usage, cleanse stormwater prior to it entering the river, and the strategies implemented for recycling and maintaining a healthy environment. DESIGNED a lighting system that will allow maximum lighting controllability. This lighting system will be energized according to events, thereby reducing the overall energy demand of the stadium.