Greening Beloit College Rooftops


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Greening Beloit College Rooftops

  1. 1. Greening Beloit’s Rooftops Menyon Heflin ENVS 250: Environment and Society Beloit College Professor Yaffa GrossmanThe History and Increasing Popularity of Green Roofs As environmental consciousness has increased in the last century, people fromacross the globe, including members of civil society, the epistemic community, industry,and the political arena, have developed interests in sustainability and so-calledsustainable development (Robinson 2004). Although “sustainable development” hascome under attacks by many academics who maintain that it is impossible to develop ina sustainable manner (Robinson 2004), many members of industry have still sought todevelop practices and products that are more environmentally friendly and reduce thenegative environmental impacts associated with consumption. While this may, in manyinstances, be a ploy to simply lure customers, some businesses do take the concept ofprotecting the environment seriously. Of the many products and practices that have come out of the environmentalmovement, one of the most notable is the so-called “green roof.” Defined byOberndorfer et al. (2007) as “roofs with a vegetated surface and substrate,” green roofs 1
  2. 2. have been gaining in popularity. Although green roofs themselves are the product ofthe last few decades, they were borne out of the roof gardens of ancient times, the mostfamous of which was, undoubtedly, the hanging gardens of present-day Syria’sSemiramis, which are now considered one of the seven wonders of the world(Oberndorfer et al. 2007). Other ancient roots of green roofs include the sod-coveredhomes of Northern Europe and those sod-roofed homes of early European settlers toAmerica’s Great Plains (Worden et al. 2004). The modern green roof, however,originated in Germany in the twentieth century (Oberndorfer et al. 2007, Worden et al.2004). Whereas in North America green roofs are just gaining in popularity and themarket for them, at present, is not very developed, they are well established throughoutEurope ( 2008, Oberndorfer et al. 2007). Despite the efforts of industryleaders in North America, green roofs remain less popular than in Europe, in partbecause many state and local governments across the continent provide a variety ofincentives ( 2008), and in some places in Germany, for example, greenroofing is a requirement (Oberndorfer et al. 2007). This has resulted in a large marketfor green roofs and related services in countries such as Switzerland, Austria, Franceand Germany, where an estimated 14% of flat roofs are now greened (Greenroofs.com2008, Van Woert et al. 2005). Today’s green roofs can be divided into two distinct categories: “intensive”green roofs and “extensive” green roofs (Kohler et al. 2001, Oberndorfer et al. 2007). 2
  3. 3. Intensive green roofs are characterized by deep substrates and diverse plantings thatmake the roof very closely resemble a traditional, ground level garden (Kohler et al.2001, Oberndorfer et al. 2007). These roofs are usually built so that roof top canfunction as additional living or working space, and they typically have greater aestheticvalue, and require more labor, than extensive green roofs (Oberndorfer et al. 2007). Incontrast, extensive green roofs have a much shallow substrate (Kohler et al. 2001,Oberndorfer et al. 2007) that typically does not exceed 10 cm (Kohler et al. 2001), andthey also require less maintenance and are more concerned with function than usablespace and aesthetics (Oberndorfer et al. 2007).The Environmental Benefits of Green Roofs Green roofs also serve a variety of environmental purposes. As populationsexpand, not only are increasingly large amounts of natural areas co-opted intocivilization, but more and more area in both the suburbs and the cities has to beconverted to impervious surfaces (Getter and Rowe 2006). Consequently, the need toreplace lost green space has become paramount in most urban settings, with green roofswidely viewed as a potential remediation technique (Getter and Rowe 2006). The services provided by green roofs are many (Oberndorfer et al. 2007,Worden et al. 2004, Getter and Rowe 2006). Green roofs can help to mitigate airpollution from diesel engines (cited in Getter and Rowe 2006). They can also reduce 3
  4. 4. sulfur dioxide and nitrous oxide in the area immediately above the green roof, andremove particulate matter that contributes to respiratory problems (Getter and Rowe2006). Green roofs can also reduce the urban heat island effect by providing shade andinsulation (Getter and Rowe 2006, Oberndorfer et al. 2007). Because this reduces theenergy required to cool buildings, it subsequently also reduces the building’s energyconsumption (Getter and Rowe 2006). The air temperature of green roof buildings canbe as much as thirty degrees Celsius cooler than that of their conventional counterparts,and as a result, residents of these green roofed buildings can reduce their total annualenergy consumption by up to 15% (Wong et al. 2003). Many scientists argue that people must take an active role in designingecosystems in the future (Palmer et al. 2004), and green roofs may be a way of doingjust that. As habitat is destroyed as a result of urbanization, green roofs can play animportant role in increasing biodiversity in highly populated areas by providing criticalhabitat (Getter and Rowe 2006, Oberndorfer et al. 2007). The creatures most likely tobenefit from green roofs are birds, insects, and microorganisms (Getter and Rowe 2006,Oberndorfer et al. 2007), many of which can be rare or endangered (Brenneisen 2006,Kadas 2006). Given the prevalence of invasive species in disturbed areas and thedisplacement of native species, some scientists think that green roofs can serve aspotential havens for increasingly threatened native plant species (Beardsley 2007, 4
  5. 5. Dewey et al. 2004, Monterusso et al. 2005), although there is considerable concern overwhether many native species can tolerate the harsh environments associated withrooftops (Getter and Rowe 2006). Other benefits of green roofs include noise reduction (Getter and Rowe 2006),increased roof lifespan (Oberndorfer et al. 2007), and improved human health forbuilding occupants (Worden et al. 2004).The Role of Green Roofs in Reducing Stormwater Runoff One of the most touted benefits of green roofs, however, is their capacity forreducing stormwater runoff, thereby preventing pollution (Getter and Rowe 2006,Kohler et al. 2001, Oberndorfer et al. 2007, Van Woert et al. 2005, Worden et al. 2004).In urban areas, the impervious surfaces of a city block cause an estimated five times asmuch runoff as a comparably-sized woodlot (Van Woert et a; 2005). Whereas only25% of rainfall is absorbed in cities, approximately 95% of rainfall is absorbed inforests (Scholz-Barth 2001). Excessive stormwater runoff causes a multitude ofproblems (Getter and Rowe 2006, Kohler et al. 2001, Oberndorfer et al. 2007, Scholz-Barth 2001, Van Woert et al. 2005., Worden et al. 2004). Urban runoff picks upharmful particles from the atmosphere above cities and from the impervious surfacesover which it flows (Van Woert et al. 2005). The contaminants in urban stormwaterrunoff are dangerous to both environmental and human health and include heavy metals, 5
  6. 6. animal wastes, pesticides, oils, salts, and a variety of nutrients which can overloadnatural systems (Getter and Rowe 2006, Van Woert et al. 2005). Runoff with manynutrients and organic matter can cause eutrophication of the water bodies into which itempties, killing many aquatic species (Getter and Rowe 2006). Excessive stormwater runoff can pose additional risks to human lives, because itincreases the likelihood of flooding (Getter and Rowe 2006). Obviously, flooding canalso cause extensive property damage, too. Large amounts of stormwater runoff canalso exceed the carrying capacity of city sewage treatment facilities, especially whenthe sewer system consists of a single pipe that routes both wastewater and sewermaterials to the treatment plants (Getter and Rowe 2006). In such so-called “combined”sewage systems, a large rainfall can cause sewage treatment facilities to overflow,dumping raw waste into rivers and streams, which poses additional threats toecosystems and to human health (Getter and Rowe 2006). Extensive runoff fromimpervious surfaces can also damage ecosystems by increasing erosion and damagingvegetation (Van Woert et al. 2005). Many people have hoped that green roofs could retain a large portion ofstormwater, thereby reducing runoff and helping to solve this ubiquitous urban problem(Van Woert 2005). Their hopes have been realized. The substrate of green roofs storeswater, which is later absorbed by the plants ( 2008). Industry estimatesfor stormwater retention are promising. Green roofs retain between 20% and 40% of 6
  7. 7. the rainfall received in winter and between 70% and 90% of the rainfall received insummer ( A study by Van Woert and colleagues confirms theseindustry statistics (Van Woert 2005). In a fourteen month study, they found that avegetated roof maintained between 69.2% to 75.6% of precipitation received duringheavy rainfalls, in which roofs received over 6 mm of rain (Van Woert 2005). In lightrainfalls of less than 2 mm precipitation, however, the green roofs retained more than96% of rainfall, and the amount of retention was 100% on several occasions (VanWoert 2005).Local Green Roofs The City of Beloit and surrounding areas have recently faced various degrees offlooding, and runoff from impervious surfaces, such as rooftops has, no doubt,contributed to these events, at least to some extent. The full impact of storm waterrunoff from rooftops, in unknown, however. In the mist of such events, the city hasbeen exhibiting great environmental concern. For example, it recently won first placeamong cities in its population category in the national American in Bloom Contest,which rates cities on beautification and environmental initiatives (City of Beloit, WI2008). Beloit’s commitment to the environment extends beyond its government andinvolves educational institutions, private citizens, and businesses. As such, Beloit iscurrently home to two green roofs, with two more planned. Both of Beloit’s green roofs 7
  8. 8. are located on the rooftops of businesses, and both of those in the works will be locatedon the rooftops of schools, including Beloit College’s new science center and BeloitMemorial High School. The city’s first green roof was constructed on the top of the ABC SupplyCompany National Headquarters in 2001, and the company, whose headquarters in onthe banks on the Rock River, has been heavily involved in green roof development inthe United States, using its combination extensive/intensive green roof as a showcase topromote green roofs and a research laboratory to further develop the technology thatmakes them possible (Green Grid Roofs 2008 a). Locally headquartered ABC SupplyCompany, Inc. was one of two collaborating firms responsible for developing theGreenGrid green roofing system that is prevalent in the United States, using itsprefabricated modules that are pre-planted and ready for installation upon arrival (GreenGrid Roofs 2008 a). Because the company is involved in developing and marketinggreen roofing systems, the rooftop is designed to be a showroom that features both theintensive and extensive roofing systems previously mentioned (Green Grid Roofs 2008a). The 10,370 ft2 local roof also serves as a laboratory, where developers test variousplants for their tolerance of the harsh rooftop environment, the insulation andstormwater runoff prevention of various combinations of plants and substrates, andother components that could be potentially incorporated into the roofing systems (GreenGrid Roofs 2008 a). 8
  9. 9. In contrast, the Neese Memorial Rooftop Garden, (completed in 2006), is a lessambitious 5,320 ft.2 intensive green roof on the top of Beloit Memorial Hospital (GreenGrid Roofs 2008 b). Whereas its local counterpart at the ABC Supply CompanyHeadquarters is only privately accessible, this roof is accessible to the public (GreenGrid Roofs 2008 b). Filled with perennials and shrubs, the garden was funded fromprivate donations, including one from ABC Supply Company, and it is designed to be asort of escape for hospital employees, patients, and their families (Green Grid Roofs2008 b).The Potential Role of Local Greenroofs in Stormwater RunoffPrevention Although these two rooftops will, undoubtedly, facilitate some reduction instormwater runoff, they are two of only a few rooftops in the City of Beloit. Althoughit is a city, Beloit, WI, has much more of a suburban character, with fewer commercialbuildings, more single-family residential homes and smaller apartment buildings, andmore side streets. Consequently, in order to determine if green roofs could actuallymake a real difference in the flood stage of the Rock River, which runs through themiddle of the city and the surrounding areas, I calculated what proportion of surfacearea is rooftops. To do this, I used aerial photographs, each consisting of 3,808 squaremillimeters of map surface. All photographs were obtained from, 9
  10. 10. and they were all taken from the same height, with the same degree of zooming, so thatI could determine the nature of the different surface features (Mapquest 2008). Usingthe grid of millimeter squares, I traced the area of roof tops for fifteen different areas,including residential, industrial, and downtown locations. Logistically, I was unable tocover the entire city of Beloit, but I tried to get a representative sample of the differenttypes of areas. Therefore, my calculations are intended to serve as a proximate estimatefor the total amount of surface area in Beloit that is covered by rooftops. I then counted how many of the millimeter squares were in rooftop andcalculated what percent of each area consisted of rooftops. Next, I averaged thepercents to get an average total percent of rooftop surface for the City of Beloit. Myresults indicate that, on average, 19.17% of the surface of Beloit, WI is covered byrooftops. This suggests that, even if all rooftops in the city were greened, a maximum ofonly about 20% of the rainfall would be prevented from running off the surface. Whilethis number seems substantial, it is small compared to the potential stormwater runoffreduction that greenroofs can provide in highly urbanized areas, where a much largerportion of the impervious surfaces and a much larger percent of the total surface area isdevoted to rooftops. It is also in these areas that greenroofs have greater impacts onheat island reduction (Getter and Rowe 2006). Furthermore, as a maximum potentialreduction in runoff, the estimated 20% is unlikely to ever be achieved. Not only are 10
  11. 11. green roofs too expensive for many residential consumers, whose homes comprise themajority of rooftop surfaces in Beloit, but the maximum runoff reduction only occursduring summer and light rainfalls (Van Woert et al 2005). Consequently, the likelihoodof the City of Beloit’s stormwater runoff ever being substantial and helping to mitigateincreasing flooding problems, is, unfortunately, highly unlikely.Works Cited:Beardsley, T. M. 2007. The Earth above. BioScience 57: 811.Brenneisen, S. 2006. Space for urban wildlife: Designing green roofs as habitats in Switzerland. Urban Habitats 4: 27-39. <>. Last accessed: 2 May 2008.City of Beloit, WI. 2008. <>. City of Beloit, WI, Beloit, WI. Last accessed: 1 May 2008.Dewey, D., P. Johnson, and R. Kjelgren. 2004. Species composition changes in a rooftop grass and wildflower meadow. Native Plants 5: 56-65.Getter, K. L. and D. B. Rowe. 2006. The role of extensive green roofs in sustainable development. Horticultural Science 42: 1276-1285.Green Grid Roofs (a). 2008. ABC Supply Company Headquarters. Green Grid Roofs. <>. Last accessed: 1 May 2008.Green Grid Roofs (b). 2008. The Neese Memorial Rooftop Garden. Green Grid Roofs. <>. Last accessed: 1 May 2008. About green roofs. 11
  12. 12. < emid=40>. Last Accessed: 1 May 2008.Kadas, G. 2006. Rare invertebrates colonizing green roofs in London. Urban Habitats 4: 66-86.Kholer, M., M. Schmidt, F. W. Grimme, M. Lear, and F. Gusmao. 2001. Urban water retention by greened roofs in temperate and tropical and climate. Technology Resource Management and Development – Scientific Contributions fir Sustainable Development 2: 151-162.Mapquest, Inc. <>. Mapquest, Inc.Monterusso, M.A., D. B. Rowe, and C. L. Rugh. 2005. Establishment and persistence of Sedum spp. and native taxa for green roof applications. Horticultural Science 40: 391-396.Oberndorfer, E., J. Lundholm, B. Bass, R. R. Coffman, H. Doshi, N. Dunnett, S. Gaffin, M. Kohler, K. K. Y. Liu, and B. Rowe. 2007. Green roofs as urban ecosystems: Ecological structures, functions, and services. BioScience 57: 823-833.Palmer, M., E. Bernhardt, E. Chornesky, S. Collins, A. Dobson, C. Duke, B. Gold, R. Jacobson, S. Kingsland, R. Kranz, M. Mappin, M.L. Martinez, F. Micheli, J. Morse, M. Pace, M. Pascual, S. Palumbi, O.J. Reichman, A. Simons, A. Townsend, and M. Turner. 2004. Ecology for a crowded planet. Science 304: 1251-1252.Robinson, J. 2004. Squaring the circle? Some thoughts on the idea of sustainable development. Ecological Economics 48: 369-384.Scholz-Barth, K. 2001. Green roofs: Stormwater management from the top down. Environmental Design & Construction 4: 63-70.Van Woert, N. D., D. B. Rowe, J. A. Andresen, C. L. Rugh, R. T. Fernandez, and L. Xiao. 2005. Green roof stormwater retention: Effects of roof surface, slope, and media depth. Journal of Environmental Quality 34: 1036-1044.Wong, N. H., Y. Chen, C. L. Ong, and A. Sia. 2003. Investigation of thermal benefits of rooftop garden in the tropical environment. Building and Environment 38: 261- 270. 12
  13. 13. Worden, E., D. Guidry, A. A. Ng, and A. Schore. 2004. Green roofs in urban landscapes. Environmental Horticulture Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Fort Lauderdale, FL. 13