City of Minneapolis Target Center Arena

Project Name: City of Minneapolis Target Center Arena Year: 2009 Owner: City of Minneapolis Location: Minneapolis, MN, USA Building Type: Commercial Type: Extensive System: Custom Size: 113000 sq.ft. Slope: 1% Access: Inaccessible, Private Submitted by: Kestrel Design Group & Greenroofs.com Designers/Manufacturers of Record: Waterproofing Membrane & Insulation: Sika Sarnafil Roofing Consultant: Inspec Landscape Architect/Greenroof Designer: Kestrel Design Group, Inc. General Contractor: Stock Roofing, a Tecta America Company Architect: Leo Daly Electric Field Vector Mapping (EFVM?): International Leak Detection (ILD) Drainage & Filter Layer: Colbond Irrigation: KISSS Water Retention Layer: American Engineering Fabrics Growth Media: rooflite? Extensive MCL Pre-Vegetated Mat Manufacturer: Sempergreen Consultation for Skyland USA (rooflite): J?rg Breuning, Green Roof Service LLC

The 20,500-seat Target Center is home of the NBA?s Timberwolves, concerts and other events, and when the Target Center Arena needed a new roof, the City of Minneapolis chose to model a sustainable building and stormwater management approach by re-roofing with a green roof. At 113,000 sf, the Target Center Arena green roof, the fifth largest extensive green roof and the first green roof installed on an arena in North America (as of August, 2009), mitigates the urban heat island effect, greens views from above, provides wildlife habitat and improves urban air quality on a scale that is not feasible at grade in an urban area like downtown Minneapolis, and will last twice as long as a conventional roof. It also mitigates stormwater runoff from a significant amount of impervious surface in a downtown location where space does not permit use of other Low Impact Development Techniques for stormwater management at grade. "Nearly 1 million gallons of storm water will be captured annually by the 2.5 acre green roof to prevent drainage into the Mississippi River," (Target Center website). Such positive impacts on local water bodies are valuable in a City that prides itself on its legendary waterbodies: The City of Lakes in the Land of 10,000 Lakes. The City of Minneapolis Target Center Arena greenroof was completed in September, 2009.

A state-of-the-art waterproofing membrane was used to withstand constant dampness, high alkalinity, and exposure to plant roots, fungi and bacterial organisms as well as varying hydrostatic pressures. To test for leaks and facilitate pinpointing the exact location of leaks throughout the roof?s lifespan so that the amount of overburden removed can be minimized, an Electric Field Vector Mapping? (EFVM?) leak detection system was installed. The Target Center green roof consists of a 2.75 inch deep growing zone in the center of the main arena roof structure and a deeper 3.5-inch growing zone around the perimeter where the structural capacity is greater to maximize the growing medium available for plant growth. The growth media used was rooflite? Extensive MCL, engineered for the Target Center by Skyland USA. A pre-grown sedum mat was supplemented with native plugs and seed to enhance plant diversity and ecological resilience and to reflect the mix of flora found in the dolomite bluffs overlooking the Mississippi and Minnesota rivers - over 30 species live on the roof. Planted with a variety of Sedums and Minnesota prairie plants including Columbine, Lanceleaf Coreopsis, Wild Strawberry, Dotted Blazing-Star, and Lupine. The lupines were planted to target the Karner Blue Butterfly, a federally listed endangered butterfly that needs lupines to survive. From afar, the pattern of the pavers that divide the growing zones reveal a design based on veins of a leaf. See the City of Minneapolis Press Release below for the complete plant lists. Designer Peter MacDonagh of the Kestrel Design Group said "There is a 20-year maintenance guarantee on the project for the vegetation?no more than four square feet of bare soil on the roof at any time,? (AIArchitect). More than 11 miles of sustainable, water-efficient irrigation lines with piping spaced every 24" were installed to water the plants during plant establishment and droughts, and 14,000 cement pavers were laid for firebreaks and roof protection. "While the project called for 50% recycling of materials, the Tecta (America) team set its own goal of recycling 100% of the old roof, resulting in an estimated 450 tons of existing rock and 590 tons of existing pavers, 140 tons of existing roofing membrane and more than 60 truckloads of existing roof insulation," (AIArchitect, see below).

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The Target Center is located at 600 North 1st Avenue, Minneapolis, MN 55403. Call 612.673.1600 or visit their website and greenroof page here, where you can also see a video of the project. The Target Center Arena received a Special Recognition Award of Excellence from Green Roofs for Healthy Ciites in 2010 - read more here (also read the cover story in the Fall 2009 Living Architecture Monitor). Read the City of Minneapolis Press Release of September 10, 2009 here, the October 19, 2009 Eco-Structure article by David Sokol "Game On" here and the October 30, 2009 AIArchitect article by Russell Boniface "Vegetated Green Roof Completed on Minneapolis? Target Center" here. For additional information regarding this project, contact L. Peter MacDonagh of the Kestrel Design Group, Inc., Green Roof Designer. Learn about the following companies in The Greenroof Directory: Skyland and rooflite?; Sika Sarnafil; Tecta America (also Stock Roofing at: http://www.stockroofing.com/); and Sempergreen. The City of Minneapolis Target Center Arena was featured in The 2010 Greenroofs of the World? Calendar for the month of April.

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