Green the Heat


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Green roof in city (Klinkenborg, 2009).


Tall buildings consisting of dark roofs and roads with black asphalt remove much of the vegetation that used to thrive there. It is now evident that these changes in the landscape caused severe environmental challenges. Urban areas became vulnerable to the impacts of climate change and the rapid expansion of the population only worsened the cause because of the demand for new accommodation made it normal to ignore existing problems. According to the U.S Census Bureau, 62.7 percent of the U.S. population now live in urban areas (“U.S. Cities are Home to 62.7% of the U.S. Population but Comprise 3.5% of Land Area”, 2015). Many of the environmental challenges in urban areas can be seen in forms of temperatures rising, worsening the urban heat island effect, and pollution from the release of CO2 into the atmosphere. All causing major health threats to citizens living in these areas and more sadly affecting children and the elderly who in many cases were diagnosed with heat related illnesses.

Urban heat island effect (UHI) is when an urban area experiences warmer day and nighttime temperatures than its surrounding rural areas. Urban areas are about 1.8-5.4° Fahrenheit warmer during the day and 22° Fahrenheit warmer during the night (“Heat Island Impacts”, 2017). UHI is already a significant problem to many U.S. cities and its residents health because the majority of the urban areas in the U.S is covered by dark roofs and asphalt. UHI works in ways that it absorbs sunlight that is radiated during the day and it converts that energy into heat causing dark surfaces to be hotter. Overall, it rises temperatures and proves low albedo in urban areas. Albedo measures how much sunlight reflects against the surface it hits. (“Albedo definition”, n.d.). Rural areas have higher albedo than urban areas because vegetation in comparison to asphalt reflects more sunlight. The decrease of albedo in urban areas accelerate UHI at an incredible pace (“Heat Island Impacts”, 2017). The cycle of low albedo in urban areas makes the natural cooling effect very difficult.

As climate change and UHI effect cause global and local temperatures to rise, the number of heat waves that U.S. cities experience is suddenly increasing in unprecedented ways (“Climate Change and Heat Islands”, n.d.). Miami for example experienced up to 46 more days over 90° Fahrenheit since 1977. It is predicted that cities like Washington D.C. will also experience a 20% increase in the number of dangerous heat days, or days over 105° Fahrenheit, by 2050 (“U.S. Faces Extreme Rise in Heat, Humidity”, 2016). Typically, in hot days, individuals find relief from heat during the nighttime because the air cools and temperature drops but with UHI affecting cities at night it is almost impossible for citizens in such areas to find any relief from the heat.

If our world leaders do not take actions, climate change will undoubtedly increase and worsen UHI. Residents in urban areas heavily rely on their air conditioning to cool themselves and spaces. But they fail to understand that they are contributing to climate change and UHI by consuming large amounts of energy. Such actions result in more CO2 to be released into the atmosphere and cause heat to be trapped in the air. Ironically, this positive feedback relationship of increasing air conditioning heats up the city even more and threatens citizens’ health (Akbari, 2005).

In 2003, a heat wave hit Europe and left at least 35,000 people dead. Most victims could have survived if their old buildings did not lack air conditioning and proper ventilation (Schär et al., 2004). The rapid increase in air conditioning usage during similar heat wave events cause power outages that leave entire city blocks without relief from the heat (De Bono, Peduzzi, Kluser & Giuliani, 2014). In the past twenty years, there’s been an increasing number of heat waves across the United States. Impoverished parts of the country where citizens cannot afford to cool their apartments during extreme hot days will be a greater risk for heat related death (“Climate Change and Heat Islands”, n.d.). The combination of climate change and UHI will be fatal to children and the elderly because children under the age of two account for 70% of heat stroke deaths (“17 Shocking Heat Exhaustion Statistics”, 2015). In fact, the center for disease control and prevention estimates that between 1979–2003, heat exposure caused about 8,000 premature deaths in the United States (“Climate Change Indicators: Heat-Related Deaths”, 2016). Citizens who are 65 and older are about three times more likely to die than younger adults from heat related illness (“Climate Change Indicators: Heat-Related Deaths”, 2016). It is important to put pressure on our politicians so we come to a solution given that 62.7% of the U.S. population now live in cities that is putting a large amount of people at risk for heat related illnesses (Li & Bou-Zeid, 2013).

Smog is a fine gaseous particle, mixed with dust and water vapor that makes the air hazy and difficult to breath. It is often caused by gas powered vehicles and industrial activities. These air pollutants that are released into our atmosphere easily form under hot conditions where there are large amounts of heavy motor vehicle operations. Smog can be responsible for a number of health defects ranging from minor respiratory illnesses to lung cancer (“What is Smog”, 2017). Minor exposure to smog over a prolonged period can cause premature deaths in densely populated areas. Once more, children and the elderly are the most vulnerable to this challenge and can easily expect cardiac and respiratory complications (“What is Smog”, 2017). Worldwide, it is estimated that each year nearly 2.5 million people die from the effects of air pollution (Rutledge et al. 2011). As a result of rising temperatures caused by climate change, the amount of smog in cities is expected to increase (What is Smog”, 2017).  

Fortunately, installing green roofs on newer constructed buildings provide a solution that would ameliorate the effects of UHI and, ultimately, climate change. Green roofs involve installing a thick layer of vegetation, soil, and a waterproof membrane on top of a building (“Green Roof Benefits”, 2016). The installation of green roofs could reduce UHI, and in turn, reduce heat related illnesses and mortality.

Temperatures in green roofs are found to be 1.9° Fahrenheit cooler than traditional roofs (Berardi & Hoseini, 2014). The vegetation in green roofs reflect more sunlight than dark surfaces and convert solar energy into biomass which then leads to an increase in albedo. Such results cause temperatures in urban areas to decrease, creating a natural cooling effect and allowing cities to experience less heat waves during hot days. Evapotranspiration causes the natural cooling effect because water is released from plant leaves and then into the atmosphere (Evapotranspiration, n.d.). Unlike concrete, areas beneath the vegetation surface are cooler thanks to evapotranspiration. Concrete on the other hand holds the heat and turns its underneath area warm which then leads to warmer outside temperatures. Such simulation is similar to buildings with green roofs versus traditional concrete roofs (Takakura, Kitade, & Goto, 2000).

As the human population keeps expanding at an accelerating pace, we must look towards the growing tide of heat in major cities so we can find new and innovative ways to reduce carbon emission (“Heat Island Impacts”, 2017). Decrease in energy consumption, carbon sequestration and storage green roofs will reduce and remove pollutants out of the atmosphere. Plants on green roofs capture airborne pollutants and noxious gases (“Green Roof Benefits”, 2016). If all the roofs in a city of the size of Detroit had green roofs, it would offset the CO2 emitted by 10,000 SUVs (Alter, 2009). Power plants are the primary emitters of pollutants. Through regulating the temperature of buildings with green roofs, it would reduce the demand of power plants and make great advances against air pollution (“Green Roof Benefits”, 2016). Installing green roofs on city blocks will improve the overall air quality of cities, make them safer and more livable.

The reduction of UHI lowers the demand for air conditioning and eventually energy costs. Since green roofs have thick layer of vegetation, the roof membrane needs to be well insulated for waterproofing or any given challenges. This method of maintaining green roofs secure help trap energy inside of the building. If 60% of a roof is covered in vegetation, 23% of the energy required to cool that building will be conserved (Peng & Jim, 2015). If a building uses less energy and maintains stable indoor temperature, less CO2 will be emitted into the air. Which soon, power plants would decrease their contribution of CO2 that has direct link on UHI.

A few cities have already begun projects with green roofs, but in order to create a difference in our whole population, we must expand this project further. The installation of green roofs in urban cities should become mandatory on some portion of all new buildings. The Toronto Green Roof Bylaw has proven to be successful and similar policies should become implemented in all cities. Specifically “the Bylaw requires green roofs on new commercial, institutional and residential development with a minimum gross floor area of 2,000 m2  ” (“Green Roof Bylaw”, n.d., para. 2). Buildings under 5,000 m2 only need to have 20% of their surface covered, with a 10% increase for every 5,000 m2 up to buildings over 20,000 m2 needing 60% of their roof covered in green roof (“Green Roof Bylaw, n.d.). The city’s sets of minimum requirements have a deeper vision for the future in which their building code standards show as example to many U.S cities. It is totally possible for us to adopt the same building code. In addition, to Toronto’s green roof policy many other cities have developed similar guidelines that have proven to be economically and environmentally successful. Toronto green roof policy only  proves that mandatory installation of green roofs do not cause any harm to the economy. The installation of green roofs in Toronto decreased the surrounding air temperature by up to 0.4° C during the day and 0.8° C by night. (Berardi, 2016). Mandating a policy similar to the Toronto bylaw not only fixes these problems but also economic benefits for residents and commercial investors. Therefore, it should be mandatory that all cities in the United States install green roofs on a certain portion of newly constructed buildings.

Many are concerned with the fact that green roofs are expensive. A green roof would cost around $15-$20 per square foot and if there was a 1,000 square foot roof and 20% (200 sq. ft.) of it was covered, it would cost about $3,000-$4,000 (“Lid Urban Design Tool-Green Roofs”, n.d.). Green roofs do cost a few thousand dollars more than conventional roofs because of the waterproof membrane and the soil and vegetation. It may not seem like a smart investment but green roofs are proven to be a much better investment than conventional roofs.

Most studies show durability in green roofs which in average doubles the lifespan of the roof membrane to at least 40 to 50 years (Nurmi, Perrels, & Lehvävirta, 2016). Traditional roofs, on the other hand, require replacement every 20-25 years (Rogers, 2015). Green roofs are replaced less often than conventional roofs, lowering the amount of payments. Also, property values increase when green roofs are installed. For example, property value in Canada and New York increased from 3.9% to 16.2% from the roofs that upgraded with green roofs practices (Veisten, et al. 2012). Green roofs reduces the need for heat and air conditioning which means a lowered heating and cooling bill for residents in urban areas. On average, buildings with green roofs decrease clients’ energy costs for over one year by about 6% (Berardi, 2016). In short, green roofs cost less in the long run and present a great economic opportunity for those installing them.

Currently, the cost to install green roofs is more than traditional roofs. However, if green roofs were to become mandated, then green roof costs would decrease in cost. For example, Germany’s four decades of sustainable policymaking encouraged local, state, and federal levels of government to act (Buehler et al, 2011). These choices led to lower costs in green roof production, because when an industry is regulated companies find ways of competing to create cheaper and more efficient products. With the advances in proactive polices, green roof installations in Germany can go for as low as $14.33/m2, while Finland has recently began installations and cost are as high as $46.93/m2 (Nurmi et al, 2016). Therefore, if U.S. cities were to mandate green roofs, the cost to install the green roofs would decrease significantly, making green roofs more affordable.

The installation of green roofs in urban areas should become mandatory to mitigate the impacts of UHI. As global temperatures increase due to climate change, the effects of UHI are becoming more intense, resulting in an increased mortality rate. Green roofs offer a solution to UHI by directly decreasing the surrounding air temperature through evapotranspiration, increasing albedo and therefore improving the lives of the citizens in urban areas.


Ralph Moreno Dos Santos Lop – Building and Construction Technology

Andrea Oliveira – Animal Science

Mira Heckmann – Geology


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Berardi, U., & Ghaffarian Hoseini, A. (2014). State-of-the-art analysis of the environmental benefits of green roofs. Applied Energy, 115, 411-428. doi:10.1016/j.apenergy.2013.10.047

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Peng, L. L. H., & Jim, C. Y. (2015). Economic evaluation of green-roof environmental benefits in the context of climate change: The case of Hong Kong. Urban Forestry & Urban Greening, 14(3), 554-561. doi:10.1016/j.ufug.2015.05.006

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Ralph Moreno Dos Santos Lop – Building and Construction Technology

Andrea Oliveira – Animal Science

Mira Heckmann – Geology



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