Urban Green Roof Agriculture

Amanda Nee, Dylan Bachand, Matt Dibara

You are standing on the streets of New York City. You look up, following the trail of light leading to the sun, currently eclipsed by the innumerous skyscrapers housing business people, families, politicians, performers, doctors, and everyone in between. Everything around you from the people to the structures is a result of maximizing potential. This is the appeal of the city. If there is space, a builder will build, and in that new building will be a new business with employees thinking up new ideas, and those new ideas will drive the developing world. But if the central dogma of urban development is in taking advantage of every inch, it is ironic that the greatest percentage of our cities’ area is not utilized at all.  Gazing up at these buildings, one can easily overlook the rooftops. Currently in New York City, 1200 acres of this rooftop area has shown potential beyond its primary shelter allocation and legislation has been passed to implement the transition (Department of City Planning, 2013). The Big Apple is home to most walks of life, but it is now time to welcome back farmers. Food will be grown on the roof. Green roofs, the practice of adding vegetation to the tops of buildings, is now widely discussed and progressively accepted. These green roofs replace the green space eliminated as cities grow and develop. With our planet reaching capacity, green roofs have the potential for our cities to once again grow and develop, this time, in a greener direction.

In 1999, the United Nations marked an important milestone by releasing a report assessing trends in world population and human geography, “The world has become increasingly urban. Currently, around 46 percent of the world population lives in urban areas; the majority of the world’s population will be urban by 2006” (United Nations, 1999). This assessment illustrates the necessity of innovation and sustainable growth in our most volatile regions. Today, more and more urbanized people are scrambling for means to decrease their carbon footprint. It is common for the public to begin reevaluating their food habits. Outside of our cities, it is becoming increasingly feasible to shop primarily at local farm markets, to keep a small garden, to compost, and to engage in ongoing dialogue about sustainable food production. If for the first time, more than half of our population will reside in cities, it is imperative that we start to make drastic changes within them.

So what is this craze about “local food”? Why has this campaign started to overshadow others that preach the humane treatment of animals or the fair treatment of laborers? One major reason for the success and acceptance of this local food movement is that its practice tends to lead to beneficial reform of these other injustices that large-scale agriculture has brought with it. Because of the cost of urban land, lower-income farmers are denied right to valuable property, and when property is obtained, it is likely that the soil may contain harsh pollutants that will affect the viability of the food and possibly the health of the consumer (Whittinghill, 2011, p. 318). Urban roof agriculture may solve this issue by making more land available and a reduced price and removing food from our cities floor, decreasing exposure to pollutants.

One must first understand a green roof in its simplest form before comprehending the modifications needed for food production. A green roof is a roof of a building that is “partially or completely covered with vegetation, and a synthetic growing medium, planted over a waterproofing membrane” (Qin et al., 2013, p. 12). It may also include additional layers such as root barriers, drainage and irrigation systems. Kortright (2011) makes the distinction, “Container gardens on roofs where plants are maintained solely in pots are not considered to be true green roofs” (p. 5). A typical extensive green roof section is depicted below in Figure 1 with all necessary components mentioned to maximize the efficiency of the system.

Figure 1: Extensive Green Roof Section

 

 

 

Green roofs serve several purposes for a building such as absorbing rainwater, providing insulation, renewing habitat for wildlife, and assisting to decrease air temperatures to mitigate the heat island effect.  There are two types of green roofs: “intensive roofs, with depths of 8-20 cm, able to support a wide variety of plants but are subsequently heavier and require more maintenance, and extensive roofs, which are lighter and equipt to sustain plants of very shallow root systems” (Kotright, 2011, p. 17). To maximize agricultural potential of these synthetic systems, “the increased soil depth of an intensive roof is essential to provide enough distance downward for the deeper roots of food bearing plants” (Oberndorfer et al., 2007, p. 6). Within this paper we will be discussing intensive green roofs.

We will illustrate a feasible means of remedying various urban conflicts that are brought on by over-concentrated living spaces while minimizing growing spaces. Green roofs have been widely implemented worldwide over the past few decades to improve overall quality of living. There are myriad discussions and revisions of the green roof design geared to maximize benefits on a structural, financial, and environmental basis. Our goal is to add on to this perfected model and offer a discussion regarding the potential for the green roofs to be a new facet of the local urban agriculture movement. The majority of current local agriculture initiatives take place on our city floors. These usually infertile, pollutant sinks are highly sought out, accessible by the highest bidder. The working of this land leads to many health and socioeconomic concerns (Whittinghill, 2011, p. 318). Existing green roofs can be altered to yield various agricultural crops to remedy the environmental, socioeconomic, and public health concerns laced in the current urban agricultural movement.

The idea of retrofitting these existing roofs needs to be handled on a case by case basis depending on the quality of the roof in place and the building beneath it. The “single most limiting factor is the weight of the soil which can exceed 100 pounds for one cubic foot of saturated soil” (Qin et al., 2013, p. 7). The benefit of converting an intensive green roof is that it is already designed with these loads factored in, so the only changes need to take place is within the soil itself. The “soil used in standard green roofs to support the grass vegetation usually is low in nitrates and is not fertilized enough to support growing vegetables” (Oberndorfer et al., 2007, p. 13). The way to convert the soil is to replace half of the existing soil with compost in 1:1 ratio and till it to aerate the soil (Kortright, 2011 p. 7). In addition, “earthworms, which enrich and aerate the soil are helpful in making the soil fertile enough to support vegetables” (Oberndorfer et al., 2007, p. 11). Once the soil is fertile enough, the plant type varies by roof climate, “roofs that heat up past 120 degrees Fahrenheit might not be suitable for cucumbers and tomatoes but will be fine for herbs such as parsley and rosemary, and plants such as the lima bean that can tolerate the hot sun” (Qin et al., 2013, p 9). To grow “cool season crops such as radishes and spinach it might be necessary to implement them with taller crops above in order to retain moisture and provide shade” (Qin et al., 2013, p. 12). Once the soil has been enhanced, all the elements exist to provide a green roof with agricultural vegetation, the type of vegetation depends on the climate suitability of the crop.

            Shifting food systems from the city floor to rooftops have numerous public health benefits. It would remove these food systems from high traffic areas. Contamination from automobile waste is a potential risk of positioning gardens within close proximity of busy roads. Oil commonly accumulates in the roads as well as debris from leaded gasoline. Decreasing exposure from both urban pollution and city visitors significantly decreases the public health risks that accompany food production (Seattle, 2013).

The soils of overly urbanized areas also retain heavy metal contaminants, byproducts of the industrial systems around them. Lead, arsenic, and oil are commonly found in urban soils at toxic concentrations (Seattle, 2013). The presence of these heavy metals alone does not correlate directly with the health risk, there are a few factors that further determine the risk to public health. One must first consider the type of plant that is being grown in this area, and determine the part of that plant that will subsequently be eaten. Whittinghill et al. (2011) cites a recent study illustrated the elevated risk of heavy metal absorption with green leafy plants due to high rates of evapotranspiration and decreased risk with fruit-bearing plants (p. 319). Typically in these urban areas, green leafy and high surface area vegetables will be a focus due to their inherent nutritional value as well as the ease at which they grow. The synthetic growing media utilized is also highly permeable and decreases the cation exchange capacity of normal soils, two factors that influence heavy metal uptake in the agricultural yield (Whittinghill, 2011, p. 319). Removing growth from the ground floor will significantly decrease the public health concern regarding heavy metal use, and nutritional benefits will be highlighted through the production of high nutrient vegetables.

The overuse of untreated municipal waste as nutrient enrichment of the soil is also a major downfall of the current ground floor urban agriculture movement. Workable land is scarce in urban areas and the land that is obtained requires great additions of fertilizers in order to come close to its production potential. Currently, the biggest concern regarding the practice of urban farming is heavy metal and pathogen contamination (Whittinghill, 2011, p. 318).  By decreasing the farmer’s need to fertilize in order to overcome barren plots, one decreases the risky use of untreated waste (Whittinghill, 2011, p. 319).

In order to grow food on these roofs the plants require fertile soil, water and seeds but they also sequester carbon as well. There has been an increase in carbon dioxide being released in our atmosphere and in fact, “According to the Intergovernmental Panel on Climate Change, carbon dioxide (CO₂ ) concentrations in the atmosphere have increased 32% since 1750” (Getter, Rowe, 2009 p.1). Carbon dioxide gas release is leading to the increase of the Earth’s temperature and causing our atmosphere to change greatly. In 2006 Michigan State professors did a research project on twelve roofs with agriculture and discovered that on average these roofs stored 162g C•m^-2 (glilal cells of carbon sequestered in a square meter). Rowe explains, “carbon is a major component of plant structures and is naturally sequestered in plant tissues through photosynthesis and into the soil substrate via plant litter and root exudates” (2010, p.21). This would be a great benefit for urban areas because of the amount of carbon that is constantly being released in those areas. With the amount of vehicles in such a small area and burning applications for fuel and energy sources urban areas tend to have an increased level of carbon dioxide being released. If we can convince other green roofs to convert their roofs in to growing food we would be able to sequester more carbon before it can be released.

One of the additional benefits of urban green roofs for agriculture is that they inevitably enhance urban biodiversity. Studies have documented that invertebrate communities can live on a variety of green roofs in several countries. Beetles, ants, bees, and spiders are among these invertebrates (Qin et al., 2013, p. 15). Insect populations are directly correlated with the plant species that are planted on green roofs. Along with insects, green roofs have been home for birds and other flight dependent animals. In addition, “extensive green roofs represent the potential for the establishment of shallow soil habitats and their accompanying biodiversity” (Kortright, 2011 p. 8). However, there have not been conclusive studies on the exact species of animals and insects, or their effect on green roofs. This is one area that could present an opportunity for future applications and research.

Green roofs used as a means of agriculture also “provide aesthetic and physiological benefits for people in urban areas” (Kortright, 2011, p. 9).  Green roofs, once converted to produce food-bearing vegetation, create a social atmosphere mimicking that of a community garden. It creates a place for social interaction, increases a sense of community ownership and stewardship. One of the most important benefits is that tending to these plants is an act of all ages and serves to bring people together from a wide variety of backgrounds (age, race, culture, social class). It also provides a “medium of healthy eating education to urban inner youth, who by capita are among the lowest in vegetable consumption” (Qin et al., 2013, p. 6).

There are many accounts where green roofs have been transformed into gardens that consistently yield crops. Students at the Univerisity of Wisconsin-Madison recently won an award for their business pitch, Sky Vegetables (Kortright, 2011, p. 7). The conceptual plan is to grow vegetables on supermarket roofs. The fresh vegetables, fruits, herbs, and flowers would be cultivated year round in rooftop gardens and sold in the supermarkets below. “Produce will be picked as it ripens, and taken to shelf in less than half an hour,” says Keith Agoada one of the three students who developed the idea.  There is a fully functioning “Sky Vegetables” as the satellite location in Madison, Wisconsin, and based on its success Keith Agoada says, “There are quite of few supermarket chains that are negotiating to the rights of Sky Vegetables”.

The Chicago City Hall green roof is another example of a green roof that eventually was transformed through the addition of agricultural crops. Chicago’s City Hall green roof when initially completed in 2001, consisted of dirt pathways and grass, and was designed as an outdoor green space for the employees of the City Hall to use to relax. It wasn’t more than two years after its implementation that workers began planting herbs and small plants such as beans and cucumbers in the areas that were once grass. Today, it stands as an outdoor oasis with areas that mimic community gardens with small plots for interested employees to grow and tend to their own plants.

Another example takes place in San Francisco at the “On Lok Senior Center, where the resident’s community garden was simply moved up eight stories when a high rise displaced it” (Qin et al., 2013, p. 7). This community garden supplies over 50 residents with vegetables such as lettuce, peppers, cucumbers, and tomatoes.

The practice of utilizing green roofs for agriculture is not something that is only prevalent in the United States, in fact Japan is viewed by many as a leader in green roof agriculture technology. The “Roppongi Hills building in Tokyo contains a rice paddy on the roof that is planted and cared for by local school children, produces 60 kilograms of rice per year” (Oberndorfer et al., 2007, p.14). This outdoor area also has a breeding colony of frogs in a water feature, and a barbecue area for corporate functions.

Unfortunately there is some opposition to implementing agriculture on urban green roofs. Rural farmers do not seem to support urban areas growing their own food because it might have the potential to take away from their livelihood. Typically farmers plant enough food to support themselves throughout the year as well as having an abundance to sell off and pay for their equipment, taxes and other expenses they come across. The majority of the clientele in urban areas have never had access or the resources to produce their own food. A local farmer from Belchertown Roy Bergeron claims, “I do believe that urban areas should have access to growing their own food but only to a certain extent, because what about the 4th or 5th generation farmers? We only know this trade and rely on selling our crops to urban areas in order to make a living, what would happen if these urban areas began to produce enough food to put us out of business?” (2013). Although many rural farmers may feel like this could potentially happen, it is not likely that urban areas will ever be able to be “net-zero” when it comes to producing food. It seems very unlikely that with the amount of people in these urban areas, that they could produce all the food they would need. There will always be a need for rural farmers to help produce food for these urban areas, we just hope that by producing their own food urban areas can reduce their carbon footprint by not solely relying on food being transported to them when they can produce some of it.  There are people out there that do not feel that urban green roof agriculture is necessary with the amount of farmers and supermarkets that we have today. However in these urban areas, grocery stores are few and far between and they also tend to be more expensive. Gittleman states that in the United States, “Inner cities largely became majority minority, immigrant, and low income, and yet most of the food stores that remained were small grocers, taken up mostly by immigrants of Asian origin seeking livelihood and a better life. These inner city grocery stores tended to have higher prices, especially on fresh produce, and they still do today” (2009, p.32-33). This leads to a food gap where in a country with so much surplus, many urban areas are “food insecure”, “a condition where people regularly run out of food or simply don’t know where their next meal will come from” (Gittleman,2009, p.33). By producing food on urban roofs this can greatly diminish the amount of people who struggle to have healthy and readily available food in their community. With a greater access to healthy, locally grown food it will improve the overall well being of the community and people should be in support of this movement.

In New York City alone there is an abundance of available space for agriculturally oriented green roofs to be implemented and the transformation is already underway. In fact, “the second largest green roof in the country residing atop the Javits Center in New York City’s West Side contains an astounding 7 acres of green space currently topped with grass vegetation” (Qin et al., 2013, p.14). Within New York City’s West Side within a five mile radius of the Javits Center are over 20 small community based gardens located on the ground, overcrowded with pedestrian traffic and obscuring buildings. One of these gardens, the First Street Green Community Garden, is depicted below. This attempt at urban agriculture has fallen victim to the challenges detailed in our argument above and would benefit significantly from the shift to higher ground.

First Street Green Community Garden- New York City, NY

 (Kotright , 2011, p, 27)

The idea is simple; utilize existing space and enhance fertile soil found on existing green roofs as an area for city dwellers to produce food. The essentials are already in place; healthy soils, fresh water, sunlight and a safe, removed area where the crops remain viable.  The funds for this type of project will come from the gardeners themselves. To take part in this system, one must pay dues to the building’s owners. This transaction, giving right of access to the roof and its resources initiate a lease of the land the same way that community gardens are funded on the City’s floor. In return, the building owner will receive free maintenance, upkeep of the rooftop vegetation, and a small profit for hosting the gardeners.  This rooftop garden can supply healthy local food to those who cultivate and care for the crops. Furthermore, formalized rental agreements that precede the use of rooftop farms would also provide the regulation and create standards that would effectively eliminate risky behaviors such as improper waste disposal and concerning agrochemical use (Whittinghill, 2011, p. 319).

It is important to clarify that this contribution to the local food movement is not a reasonable means to completely liberate cities from their outsourcing needs. These rooftop gardens, still in the early stage of general public acceptance, will not yield enough crops for profit, but this is not the intention. Studies show that green roof agriculture can be more profitable and yield more crops than standard rural farming and this is because  “urban farms are worked more intensely, they can produce up to 15 times more per acre than their rural counterparts” (Qin et al., 2013, p. 18) There are extensive possibilities for further research in this area. Our discussion on rooftop agriculture is to be viewed in the same way as a small garden in the backyard of a suburban home. These gardens do not significantly decrease weekly shopping trips, nor do they yield a profit. However, they provide a small source of local, healthy food and provide satisfaction to their caretakers.  Urban workers and residents desire this same satisfaction, and the means of production is now within reach. It is essential that we begin to merge the green roof movement with this innovative urban agricultural system. In this way the ability to live an environmentally conscious, healthy, and satisfying urban life doesn’t stop where the city begins.

 

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