Green Roofs: The Future of Combating UHI

Green roofs add a beautiful shade of natural green to a dull urban environment.


Skyler Hall – Plant, Soil, and Insect Sciences

Joseph Lyons – Building Construction Technology Sciences

Anthony Tiso – Pre-Veterinary Sciences

University of Massachusetts, Amherst



HOOK!!!!! Located in Southern California, Los Angeles [LA] is one of the most popular tourist destinations in the United States and draws in millions of people annually. In 2016 alone, nearly 46 million people visited the city (CBS Los Angeles, 2016). LA is the second largest city in the America, rivaled only by New York City. According to Population USA (2019), in the most recent census survey, Los Angeles has a resident population size of roughly 4 million people and it is estimated that by the summer of 2019 it could potentially rise well over that number. It is predicted that by 2050, the population will have increased by 3.5 million people (World Population Review, 2019). This ever increasing population of the city has a significant impact on cities and the urban environment. Increased buildings lead to higher temperatures through trapped carbon emissions, lack of vegetation, and decreased albedo. All of these factors lead to the Urban Heat Island Effect [UHI]. The urban/city area is significantly warmer than the  surrounding suburban and rural areas. In some cases it was noted that temperatures in major cities could be as much as 22℉ hotter in the evenings compared to the surrounding areas (North Carolina Climate Office, 2019).


As populations and urbanization in the city continues to increase more buildings are erected, more roadways built, and more cars brought in for transportation. Subsequently, more green spaces and vegetated areas become isolated pockets. As these green spaces become more limited and  man-made infrastructure is made more prominent, it causes temperatures in the city to rise even further  due to more energy being consumed and emitted in order to heat and cool buildings, along with the increase in carbon emission from cars and other transportation. (Razzaghmanesh, Beechman, & Salemi, 2016). This is caused by albedo. Albedo is one of the major factors in increasing the temperatures in urban areas. It is defined by the amount of light, mainly sunlight, that hits a surface and is transmitted back out without being absorbed by that material (North Carolina Climate Office, 2019a). This means that materials that have a high albedo, which include most man-made building materials, absorb heat and trap it within the city rather than releasing it back into the atmosphere.

The burning of fossil fuels causes Carbon dioxide concentration in the atmosphere to increase, which raises temperatures. The trapped carbon dioxide is one of the primary gases responsible for trapping heat in Earth’s atmosphere and one of the leading causes of man-made climate change (National Aeronautics and Space Administration, 2019). Rising temperatures lead to dramatic changes in the climate which cause erratic weather patterns including droughts, floods, wildfires, severe storms which can be seen in California and beyond (County of Los Angeles Public Health, 2019). In 2018 California saw one of the worst series of wildfires in the state’s history: The Camp, The Woolsey, and Hill Fires. In total these fires burned roughly 231,000 acres of land and caused roughly 50 deaths (CBS News, 2018). Increasing temperatures are responsible for the droughts and increasingly dry weather conditions that California is experiencing which lead to the severe fires that have been occuring. High temperatures are especially centered around urban areas and noticeably greater than surrounding rural areas. As mentioned previously, the burning of fossil fuels contributes to excess carbon dioxide in the atmosphere. The trapped carbon dioxide is especially high in areas where there is a lot of fossil fuel usage, e.i. urban areas and large cities.

Because UHI is caused by the raising of air temperatures, it affects the amount of energy needed to heat and cool buildings. By increasing outdoor air temperatures by a few degrees average, this phenomenon can drastically affect the temperate needs of the indoor environments in buildings. As temperatures increase, the usage of cooling systems also increase, especially during the warmer months of summer. It would appear that there is a circular relationship between the Urban Heat Island Effect and building energy demands. Heating and cooling systems are mainly powered by fossil fuels, such that as energy demand to maintain building temperature increases so does the UHI and vise versa. If this continuous feedback loop can be broken or slowed it will significantly decrease the need for fossil fuels to cool buildings  in urban areas and in a larger scale, globally. If buildings were equipped with a green roof, the UHI effect could be dramatically decreased. Green roofs would not only help with the sequestration of excess carbon in the urban atmosphere by having the plant species absorb the carbon, but reduce the usage of fossil fuels through passive cooling (evapotranspiration) and reduce albedo, which is the reflection of solar radiation that could be absorbed by the green surface. Understanding the dynamic system between the burning of fossil fuels and UHI is essential to understanding how to slow climate change in urban environments.

As time progresses, UHI will continue to increase and the changes in the the environment will become more severe, which will negatively affect quality of life in urban environments. Quality of life will begin to be impacted because of the increase in air pollutants in the atmosphere due to the ability of carbon to trap in heat and will then cause a smog over the area. Green roof surfaces will help reverse these effects of climate change in urban environments and improve daily lives by helping to mitigate the use of fossil fuels for cooling systems. If more green roofs are implemented they would have the ability to help help uptake excess carbon in the atmosphere surrounding the city. We propose the implementation of intensive green roofs on commercial buildings will help to reduce the UHI effect in Los Angeles. If Los Angeles begins to initiate policies that building owners can receive grants towards the cost of building a green roof it will increase the amount of green roofs in the city.

An intensive green, which is a vegetation covered roof that has a soil depth of 6 inches or more, a weightload that is up to 150 lbs/ft2, this roof may include trees or scrubs, and requires irrigation, fertilization, and more maintenance compared to an extensive roof (Plant Connection, Inc 2019). The cost will inevitably rise if you need to employ a landscape gardener to design the roof for you, which is common when installing a green roof onto a larger surface. The quantity and type of plant species you decide to implement will also be factored into the cost. The most common low growing plant species are much cheaper, than those roofs that wish to be fit with larger plants or trees.

Many cities around the United States are beginning to branch out into the expanding market that is green roofs. At the forefront of the green wave are the cities of  New York City and Philadelphia. In New York City there have been a a number of ways that lawmakers have tried to get building owners to implement green roofs into their buildings. Building a green roof is no small nor inexpensive task. In NYC they are offering grants that will incur the cost of building the green roof for the building owners (Schaeffer, 2018). By allowing grants to go towards the building of green roofs, NYC hopes to increase the amount of green roofs in the booming metropolis. By having grants made to go towards the building of green roofs, NYC hopes to increase the amount of green roofs in the booming metropolis. As well as grants many urban cities are also implementing tax breaks and other monetary incentives to build green roofs. For example, the Philadelphia Department of Revenue (2018) initiated the “Green Roof Tax Credit”, which will allow for building owners to to get back half (50%) of the cost of building a green roof that supports vegetation up to $100,000. The implementation of tax deductions and abatements for the building of green roof surfaces gives a monetary incentive to build these beneficial structures. This will most likely increase building owner’s willingness to care about green roofs  if it benefits them in the short term as well as having a monetary cost taken out in taxes. According to Thering (2017) at the University of Minnesota, the price that can be incurred from building a green roof can be upwards of $464,000 whereas a traditional roof may only cost $335,000. This can be especially important for commercial buildings and warehouses where a lot of resources are being used to maintain the temperatures in these facilities. On average, Walmart Super centers can range anywhere from 180,000 to 250,000 ft2 (Institute for Local Self-Reliance, 2008). As one could imagine, heating and cooling this building takes a tremendous amount of energy to regulate temperature, which ultimately comes from the burning of fossil fuels. If properly installed, it is estimated that green roofs could save nearly $200,000 (Thering, 2017). This number is dependent on many factors including roof size, plant type, and region in which the building is located. In an experiment to test the effectiveness of the cooling capacity of green roofs, Jim (2015) tested two experimental plots on the roof of an apartment building. A perennial peanut variety, sedum, and a control plot were used in this experiment. The air conditioning use of the vacant apartment below was monitored. Data showed that the control plot (bare roof) had and energy consumption of 67.02 kW as compared to the the perennial peanut and sedum plots which used 67.16 kW and 54.00 kW of energy respectively (Jim, 2015, p. 66). This experiment demonstrates the possible cooling power that plants can have on buildings. This form of cooling is known as passive cooling because it does not take an outside energy input in order to function.

New York City is using April 22nd, also known as “Earth Day”, which is the largest environmental movement in the world (Earth Day Network, 2019) as a means on pushing for the installation of green roofs in the boroughs. This day each year, is one specifically dedicated to reducing waste, energy, and pollution. This provides the city officials with a structured day of environmental promotion and a greater way to address the public if they have not heard of this growing movement. The approval for funding and public outreach to educate the public about how these surfaces not only affect the environment, but the cities infrastructure such as tunnels and roads will be a driving factor for the city. Many officials speak on behalf of the water run off and storm water that accumulates into the city which is important since NY is surrounded by water. The excess water that would be reduced by the planted surfaces would help reduce flooding in the streets as well as the construction of the structures that are under constant ware. The available space, specifically on the roofs of the numerous buildings in the city has yet to be tapped into yet according to Congressman Joe Crowley (NYC EPA 2019). Since the city has such a large amount of open roof space, New York could be a great place to start a big movement that could provide the influence for other cities to join.

Building green roofs also come with a myriad of possibilities and benefits for a large city like New York. With a green roof, they get to see plant life everyday. Green roofs are also beneficial to marketing standards, where communities are interested in companies that are willing to install a roof with the mindset of saving the environment. (Cooper, 2018). Insulation also goes up with the installation of a green roof. Green Roofs also assist in dampening noise. The multifaceted surfaces of plants and porous nature of the material help to both deflect and absorb noise not only of the city but can also assist in dampening rooftop mechanical equipment (Cooper, 2018). An extensive green roof has been shown to decrease surrounding noise levels by 40 decibels (Vegetal i.D. ®, n.d.).

Some would argue that green roofs are an unrealistic measure of affecting climate change for a number of reasons including: the major cost, their effectiveness, and where they can be built. As aforementioned, there is an inherently high cost to building a green roof, as there is much planning and mapping out that must occur before installing a green roof into a building.     An intensive green, which is defined by a roof that has a soil depth of 6 inches or more, a weightload that is up to 150 lbs/ft2, this roof may include trees or scrubs, and requires irrigation, fertilization, and more maintenance compared to an extensive roof. An extensive roof has a soil depth of 3-6 inches, much lighter in weight ranging from 15-50 lbs/ft2 , limited plant species to be planted, and lower requirement of maintenance, irrigation, and nutrient requirements (Plant Connection Inc., 2019). Extensive green roofs also tend to be simpler, primarily using hardy little plants. These types of roofs require least amounts of added structural support, as compared to an intensive roofs. The plus side of this roof is the little amount of maintenance needed. (Environmental Protection Agency, 2019). Extensive green roofs have limited energy efficiency, and the plant types used are limited. They also do not provide the recreational ability that intensive green roofs exhibit (Hammond, n.d.). Intensive green roofs, on the other hand, are more complex. Some intensive green roofs are even fully accessible to the public and have trees growing on them. These roofs require much more structural support due to the increased weight of the larger plants and foot-traffic of people. The cost goes up with all of these factors present, and the labor and maintenance required is much greater than that of an extensive green roof (EPA, 2019). While there are benefits to intensive green roofs, disadvantages are included as well. The complex irrigation systems for some larger intensive green roofs are expensive and difficult to maintain. The larger diversity of the plants also increase cost and maintenance, making this much more time consuming than its extensive counterpart. The added load drives the cost up even higher, and the roof now needs an elaborate and intricate drainage system for water collection and removal. (Hammond, n.d.).

A way to improve upon the structure of a green roof is by adding a type of roof structure that allows one to build a green roof without having to remodel the building’s existing roof. Most of the population first thinks of building these roofs using a flat roof, which is by far the most common type of green roof structure. Yet, some small roofing businesses have developed a type of grid system that holds a green roof on a steeply sloped roof. Small cells are connected to metal rods that wrap over the peak of the roof, and then the roof has small footholds into the roof. The cell depth ranges from around four inches to eight inches deep to incorporate the soil which holds the plant life. (Green Roof Solutions, 2019).

As the green spaces become increasingly rare in large cities it is important to try to reclaim that vegetation. Studies have shown that there is a direct correlation between cooler air temperatures in cities and vegetation. Meaning, that in parts of New York City where there was more vegetation present it was documented that the air temperature was reduced. In fact, it was found that when compared to areas that were mostly m

As environmental protection and sustainability movements continue grow throughout the years, green roofs are on the forefront of generating a great impact on the urban heat island effect. Green roofs, if implemented into Los Angeles will have a significant positive impact on the urban environment by reducing the Urban Heat Island Effect. Many major cities have already begun the process of installing these systems into their communities. By bringing green spaces into the




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  3. Great article! Green roofs are a fantastic solution for combating the urban heat island effect and promoting sustainability in urban areas. I actually recently wrote an article on “zero waste at the workplace” and I think incorporating green roofs into office buildings could be a great way to reduce waste and promote eco-friendly practices. Thank you for highlighting the importance of green roofs in combating UHI!

  4. Green roofs are becoming increasingly popular as a means of combating the urban heat island (UHI) effect, which is a phenomenon where urban areas experience higher temperatures than surrounding rural areas. By incorporating vegetation and soil into a building’s roof, green roofs can reduce heat absorption and improve air quality. In addition to their environmental benefits, green roofs can also provide insulation, reduce noise pollution, and even serve as recreational spaces. While the initial cost of installing a green roof can be higher than traditional roofing materials, the long-term benefits and potential cost savings make them an attractive option for many building owners and developers. As cities continue to grow and the effects of climate change become more pronounced, Loodgieter Amsterdam green roofs may become an increasingly important tool for combatting the UHI effect and promoting sustainable development.

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