Mar 26, 2018

Storm Water Shootout

New Chicago Blackhawks facility meets sustainability goals with green roof

New Chicago Blackhawks facility meets sustainability goals with green roof

Chicago: where deep-dish pizza, fluctuating temperatures and worshipped sports teams collide. The new MB Ice Arena on the city’s Near West Side addresses at least two of these characteristics. The facility features a green roof capable of weathering hot Chicago summers and blustery Midwest storms, and it is the new home of the Chicago Blackhawks. It may even serve deep-dish pizza, too. 

The Sustainable City

“Chicago kind of hangs their hat on being the leader in green roofs,” Kevin Serena, garden roof technical sales coordinator for American Hydrotech, told SWS.

Within city limits, Chicago boasts more than 500 green roofs, covering nearly 5.6 million ft, according to the city of Chicago. The city encourages such projects on new developments, with the Chicago Sustainable Development Policy and the Chicago Stormwater Ordinance Manual providing guidance. According to the city, the goal of the Chicago Sustainable Development Policy is to “enhance the sustainable performance of projects receiving city assistance. It requires development projects that are receiving financial assistance or special approvals from the city to include sustainable elements.” The policy includes a point system for two compliance paths: projects not certified through a listed building certification and projects seeking building certification. Green roofs contribute quite a few points to the projects, making it easier for new developments to comply with the policy. According to Serena, the Chicago Sustainable Development Policy requires at least 50% of new construction roofs to be green.

In its Chicago Stormwater Ordinance Manual, the city also recommends green roofs as a volume control best management practice (BMP). It offers a guide sheet, which includes design guidelines, minimum design requirements, maintenance guidelines and a worksheet for quantifying BMP performance for building to comply with the Chicago Stormwater Management Ordinance. The resources help individual projects and make the city greener.

New Chicago Blackhawks facility meets sustainability goals with green roof

There are more than 500 green roofs in Chicago.

Urban Jungle

Northeast Illinois averages 36.83 in. of precipitation annually. While the Metropolitan Water Reclamation District of Greater Chicago develops sprawling flood control projects, notably the Tunnel and Reservoir Plan, Chicago sewers still experience stress. Chicago uses a combined sewer system, meaning one underground sewer system conveys both wastewater and storm water to treatment plants. When there is an excess of storm water during a large rain event, the sewers overflow and release untreated wastewater and storm water to the Chicago River, which can be harmful to the environment. Any less strain on the system makes a difference. Thus, green infrastructure, like green roofs, are a worthy and sustainable investment.

According to Serena, green roofs:

  • Retain a portion of the storm water until the roofing assembly is completely saturated;
  • Delay the release of excess storm water from the building roof into a site storm water system to reduce issues related to peak flow; and
  • Reduce the overall volume of storm water through evapotranspiration of the plant material.

Despite cold Chicago winters, green roofs offer year-round storm water management. In addition, green roofs reduce noise and air pollution in urban environments. They also help cities manage the urban heat island effect. Temperature increases in urban areas are greater than in suburban areas due to the volume of roadways, parking lots and rooftops in cities, which typically are made of dark materials that absorb heat from the sun. Green roofs counteract this.

“Through the plant material, there is actually a cooling effect,” Serena said. “There have been some studies done that show green roofs have been somewhere between 40°F and 60°F cooler than the conventional roofing system.”

Green roofs are favored by building owners, as well. They protect the roofing membrane from ultraviolet deterioration, thus extending the life of the membrane. While some roofing membranes may last 10 to 15 years, a green roof can extend this to more than 50 years, Serena said, saving the building owner money.

New Chicago Blackhawks facility meets sustainability goals with green roof

Black & Green & Red All Over

The MB Ice Arena project goal was to meet or exceed Chicago’s policy targets. The arena, which opened in fall of 2017, is a 125,000-sq-ft facility serving as a training location for the Chicago Blackhawks, as well as a community space for recreational use. Located just south of the United Center, the arena will house local high school teams and offer hockey classes and leagues, public skate, fundraising, and more. It is a $65-million facility, according to the Chicago Sun Times.

The arena features two levels of green roofs. It uses an American Hydrotech Extensive Garden Roof assembly, which covers 24,000 sq ft and can hold nearly 22,000 gal of storm water, providing relief to the city’s storm sewers and meeting Chicago Sustainable Development Policy. To make the project possible, several parties had to work in tandem: the architect, HOK; the general contractor, James McHugh Construction; the roofing applicator, All American Exterior Solutions; the garden roof applicator, Christy Webber Landscapes; and the manufacturer, American Hydrotech. During installation, the crews experienced little to no major challenges.

This project used sedum mats for vegetation. The 25-sq-ft mats include 12 to 16 different varieties of sedum, a leaf succulent plant. The diverse varieties create an appearance that changes year-round, as the varieties will bloom at different points in the year. What’s more, sedum mats are a relatively inexpensive option.

According to Jim Waldschmidt, account manager for Christy Webber & Co., sedum mats were selected due to budgetary concerns. Time played a role, as well. Sedum mats do not require waiting or maintenance time for growth. Unlike some green roofs that offer only 80% coverage upon installation, sedum mats offer nearly 95%, immediately.

“It is instant green,” Willie Hedrick, division manager for All American Exterior Solutions, told SWS.

This instant coverage requires less maintenance for the contractor or building owner. Because the plugs are established so quickly, there is less threat of the plant material dying with neglect and becoming a “brown roof,” Hedrick said. Sedum prevents this. “It’s pretty hard to kill,” he added.

However, getting to this instant coverage involved several steps. First, a watertight waterproofing membrane was applied using hot rubberized asphalt, which is applied as a liquid, preventing seams.

“On the vegetative roof, you’re going to have contact with water, whether it be rainwater or when you’re irrigating a vegetative roof to get the plants established … The membrane is going to have water exposure," Serena said. "So that’s why hot rubberized asphalt is ideal for vegetative roof membranes.”

The membrane is followed by the root barrier layer, an extruded insulation layer, a water retention and drainage layer, a filter fabric, the engineered growing media and, finally, the vegetation (see Figure 1). Unlike many green roofs, this roofing application uses engineered growing media rather than traditional topsoil. Topsoil is made of organic material, whereas the engineered growing media is more lightweight and less likely to break down over time. In Chicago, the engineered growing media uses expanded clay, sand and compost. The roof includes small cups—a 4-in. retentive assembly—that hold water to sustain plants in times of drought and help with storm water management. The system holds more than 1.5 in. of water per square foot, and, as a 24,000-sq-ft project, the water retention adds up quickly.

“It was a pretty significant project,” Serena said.

New Chicago Blackhawks facility meets sustainability goals with green roof

The MB Ice Arena features two levels of green roofs, which use sedum mats for vegetation. Multiple varieties of the plant will bloom at different points in the year.

Green Roof Goaltender

Once a green roof is installed, most of the work is done. A sedum roof is very low maintenance. There will be a short establishment period requiring some maintenance to promote root growth, but sedum will then operate of its own accord.

“[Sedum] is a very drought-tolerant plant. It requires little to no irrigation,” Serena said. “Typically, the amount of precipitation we’re getting in Chicago doesn’t require irrigation of the plant material.”

After the establishment period, the green roof may require some weeding, fertilizing and drain cleaning, Hedrick added, but it is generally an attractive option. American Hydrotech places the roof under warranty for up to 25 years, but the vegetation can last for as long as it is being maintained. It was a project that, ultimately, met its goal. 

About the author

Lauren Baltas is managing editor of SWS. Baltas can be reached at [email protected].