Greening Beloit College Rooftops

Greening Beloit’s Rooftops
Menyon Heflin
ENVS 250: Environment and Society
Beloit College
Professor Yaffa Grossman

The History and Increasing Popularity of Green Roofs

As environmental consciousness has increased in the last century, people from

across the globe, including members of civil society, the epistemic community, industry,

and the political arena, have developed interests in sustainability and so-called

sustainable development (Robinson 2004). Although “sustainable development” has

come under attacks by many academics who maintain that it is impossible to develop in

a sustainable manner (Robinson 2004), many members of industry have still sought to

develop practices and products that are more environmentally friendly and reduce the

negative environmental impacts associated with consumption. While this may, in many

instances, be a ploy to simply lure customers, some businesses do take the concept of

protecting the environment seriously.

Of the many products and practices that have come out of the environmental

movement, one of the most notable is the so-called “green roof.” Defined by

Oberndorfer et al. (2007) as “roofs with a vegetated surface and substrate,” green roofs

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have been gaining in popularity. Although green roofs themselves are the product of

the last few decades, they were borne out of the roof gardens of ancient times, the most

famous of which was, undoubtedly, the hanging gardens of present-day Syria’s

Semiramis, 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-covered

homes of Northern Europe and those sod-roofed homes of early European settlers to

America’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 the

market for them, at present, is not very developed, they are well established throughout

Europe (Greenroofs.com 2008, Oberndorfer et al. 2007). Despite the efforts of industry

leaders in North America, green roofs remain less popular than in Europe, in part

because many state and local governments across the continent provide a variety of

incentives (Greenroofs.com 2008), and in some places in Germany, for example, green

roofing is a requirement (Oberndorfer et al. 2007). This has resulted in a large market

for green roofs and related services in countries such as Switzerland, Austria, France

and Germany, where an estimated 14% of flat roofs are now greened (Greenroofs.com

2008, 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).

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Intensive green roofs are characterized by deep substrates and diverse plantings that

make 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 can

function as additional living or working space, and they typically have greater aesthetic

value, and require more labor, than extensive green roofs (Oberndorfer et al. 2007). In

contrast, 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), and

they also require less maintenance and are more concerned with function than usable

space and aesthetics (Oberndorfer et al. 2007).

The Environmental Benefits of Green Roofs

Green roofs also serve a variety of environmental purposes. As populations

expand, not only are increasingly large amounts of natural areas co-opted into

civilization, but more and more area in both the suburbs and the cities has to be

converted to impervious surfaces (Getter and Rowe 2006). Consequently, the need to

replace lost green space has become paramount in most urban settings, with green roofs

widely 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 air

pollution from diesel engines (cited in Getter and Rowe 2006). They can also reduce

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sulfur dioxide and nitrous oxide in the area immediately above the green roof, and

remove particulate matter that contributes to respiratory problems (Getter and Rowe

2006).

Green roofs can also reduce the urban heat island effect by providing shade and

insulation (Getter and Rowe 2006, Oberndorfer et al. 2007). Because this reduces the

energy required to cool buildings, it subsequently also reduces the building’s energy

consumption (Getter and Rowe 2006). The air temperature of green roof buildings can

be 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 annual

energy consumption by up to 15% (Wong et al. 2003).

Many scientists argue that people must take an active role in designing

ecosystems in the future (Palmer et al. 2004), and green roofs may be a way of doing

just that. As habitat is destroyed as a result of urbanization, green roofs can play an

important role in increasing biodiversity in highly populated areas by providing critical

habitat (Getter and Rowe 2006, Oberndorfer et al. 2007). The creatures most likely to

benefit 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 the

displacement of native species, some scientists think that green roofs can serve as

potential havens for increasingly threatened native plant species (Beardsley 2007,

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Dewey et al. 2004, Monterusso et al. 2005), although there is considerable concern over

whether many native species can tolerate the harsh environments associated with

rooftops (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 for

building 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 for

reducing 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 as

much runoff as a comparably-sized woodlot (Van Woert et a; 2005). Whereas only

25% of rainfall is absorbed in cities, approximately 95% of rainfall is absorbed in

forests (Scholz-Barth 2001). Excessive stormwater runoff causes a multitude of

problems (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 up

harmful particles from the atmosphere above cities and from the impervious surfaces

over which it flows (Van Woert et al. 2005). The contaminants in urban stormwater

runoff are dangerous to both environmental and human health and include heavy metals,

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animal wastes, pesticides, oils, salts, and a variety of nutrients which can overload

natural systems (Getter and Rowe 2006, Van Woert et al. 2005). Runoff with many

nutrients and organic matter can cause eutrophication of the water bodies into which it

empties, killing many aquatic species (Getter and Rowe 2006).

Excessive stormwater runoff can pose additional risks to human lives, because it

increases the likelihood of flooding (Getter and Rowe 2006). Obviously, flooding can

also cause extensive property damage, too. Large amounts of stormwater runoff can

also exceed the carrying capacity of city sewage treatment facilities, especially when

the sewer system consists of a single pipe that routes both wastewater and sewer

materials 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 to

ecosystems and to human health (Getter and Rowe 2006). Extensive runoff from

impervious surfaces can also damage ecosystems by increasing erosion and damaging

vegetation (Van Woert et al. 2005).

Many people have hoped that green roofs could retain a large portion of

stormwater, thereby reducing runoff and helping to solve this ubiquitous urban problem

(Van Woert 2005). Their hopes have been realized. The substrate of green roofs stores

water, which is later absorbed by the plants (Greenroofs.com 2008). Industry estimates

for stormwater retention are promising. Green roofs retain between 20% and 40% of

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the rainfall received in winter and between 70% and 90% of the rainfall received in

summer (Greenroofs.com). A study by Van Woert and colleagues confirms these

industry statistics (Van Woert 2005). In a fourteen month study, they found that a

vegetated roof maintained between 69.2% to 75.6% of precipitation received during

heavy rainfalls, in which roofs received over 6 mm of rain (Van Woert 2005). In light

rainfalls of less than 2 mm precipitation, however, the green roofs retained more than

96% of rainfall, and the amount of retention was 100% on several occasions (Van

Woert 2005).

Local Green Roofs

The City of Beloit and surrounding areas have recently faced various degrees of

flooding, 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 water

runoff from rooftops, in unknown, however. In the mist of such events, the city has

been exhibiting great environmental concern. For example, it recently won first place

among cities in its population category in the national American in Bloom Contest,

which rates cities on beautification and environmental initiatives (City of Beloit, WI

2008). Beloit’s commitment to the environment extends beyond its government and

involves educational institutions, private citizens, and businesses. As such, Beloit is

currently home to two green roofs, with two more planned. Both of Beloit’s green roofs

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are located on the rooftops of businesses, and both of those in the works will be located

on the rooftops of schools, including Beloit College’s new science center and Beloit

Memorial High School.

The city’s first green roof was constructed on the top of the ABC Supply

Company National Headquarters in 2001, and the company, whose headquarters in on

the banks on the Rock River, has been heavily involved in green roof development in

the United States, using its combination extensive/intensive green roof as a showcase to

promote green roofs and a research laboratory to further develop the technology that

makes them possible (Green Grid Roofs 2008 a). Locally headquartered ABC Supply

Company, Inc. was one of two collaborating firms responsible for developing the

GreenGrid green roofing system that is prevalent in the United States, using its

prefabricated modules that are pre-planted and ready for installation upon arrival (Green

Grid Roofs 2008 a). Because the company is involved in developing and marketing

green roofing systems, the rooftop is designed to be a showroom that features both the

intensive and extensive roofing systems previously mentioned (Green Grid Roofs 2008

a). The 10,370 ft2 local roof also serves as a laboratory, where developers test various

plants for their tolerance of the harsh rooftop environment, the insulation and

stormwater runoff prevention of various combinations of plants and substrates, and

other components that could be potentially incorporated into the roofing systems (Green

Grid Roofs 2008 a).

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In contrast, the Neese Memorial Rooftop Garden, (completed in 2006), is a less

ambitious 5,320 ft.2 intensive green roof on the top of Beloit Memorial Hospital (Green

Grid Roofs 2008 b). Whereas its local counterpart at the ABC Supply Company

Headquarters is only privately accessible, this roof is accessible to the public (Green

Grid Roofs 2008 b). Filled with perennials and shrubs, the garden was funded from

private donations, including one from ABC Supply Company, and it is designed to be a

sort of escape for hospital employees, patients, and their families (Green Grid Roofs

2008 b).

The Potential Role of Local Greenroofs in Stormwater Runoff

Prevention

Although these two rooftops will, undoubtedly, facilitate some reduction in

stormwater runoff, they are two of only a few rooftops in the City of Beloit. Although

it is a city, Beloit, WI, has much more of a suburban character, with fewer commercial

buildings, more single-family residential homes and smaller apartment buildings, and

more side streets. Consequently, in order to determine if green roofs could actually

make a real difference in the flood stage of the Rock River, which runs through the

middle of the city and the surrounding areas, I calculated what proportion of surface

area is rooftops.

To do this, I used aerial photographs, each consisting of 3,808 square

millimeters of map surface. All photographs were obtained from www.mapquest.com,

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and they were all taken from the same height, with the same degree of zooming, so that

I could determine the nature of the different surface features (Mapquest 2008). Using

the 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 to

cover the entire city of Beloit, but I tried to get a representative sample of the different

types of areas. Therefore, my calculations are intended to serve as a proximate estimate

for 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 and

calculated what percent of each area consisted of rooftops. Next, I averaged the

percents to get an average total percent of rooftop surface for the City of Beloit. My

results indicate that, on average, 19.17% of the surface of Beloit, WI is covered by

rooftops.

This suggests that, even if all rooftops in the city were greened, a maximum of

only about 20% of the rainfall would be prevented from running off the surface. While

this number seems substantial, it is small compared to the potential stormwater runoff

reduction that greenroofs can provide in highly urbanized areas, where a much larger

portion of the impervious surfaces and a much larger percent of the total surface area is

devoted to rooftops. It is also in these areas that greenroofs have greater impacts on

heat island reduction (Getter and Rowe 2006). Furthermore, as a maximum potential

reduction in runoff, the estimated 20% is unlikely to ever be achieved. Not only are

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green roofs too expensive for many residential consumers, whose homes comprise the

majority of rooftop surfaces in Beloit, but the maximum runoff reduction only occurs

during summer and light rainfalls (Van Woert et al 2005). Consequently, the likelihood

of the City of Beloit’s stormwater runoff ever being substantial and helping to mitigate

increasing 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.
<http://www.urbanhabitats.org.vo4n01/index.html>. Last accessed: 2 May 2008.

City of Beloit, WI. 2008. <http://www.beloit.ci.wi.gov>. 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.
< http://www.greengridroofs.com/projects/commercial/projects_ggpilot.htm>. Last
accessed: 1 May 2008.

Green Grid Roofs (b). 2008. The Neese Memorial Rooftop Garden. Green Grid Roofs.
< http://www.greenroofs.com/projects/pview.php?id=690>. Last accessed: 1
May 2008.

Greenroofs.com. 2008. About green roofs. Greenroofs.com.

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<http://www.greenroofs.org/index.php?option=com_content&task=view&id=26&It
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. <www.mapquest.com>. 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.

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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.

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Greening Beloit College Rooftops

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