Getting Off the Ground

Rooftop Gardening on UW-Madison

Scenario

In the past several years, key stakeholders at the University of Wisconsin-Madison have researched and discussed the feasibility of implementing campus rooftop gardens on one of the buildings on campus. Specifically, Union South’s roof was analyzed for potential use in rooftop farming by Silva et al (2014). Included in the project were yield trials and water quality testing of run-off irrigation water for leafy green production using different growing media, as well as estimated start-up costs.

Although the conversation about implementing a rooftop garden on Union South has largely gone dormant in the last couple of years, the UW would like to further explore the environmental, economic, and social aspects of sustainability that can be achieved through rooftop farming while some momentum remains. As a team, we were asked to compile evidence on the sustainability impacts of rooftop gardening both generally and in a campus setting specifically. Using Erin Silva’s study as a basis, our project also took a specific look at Union South as a model for implementing present and future rooftop gardens on the campus.

Abstract

For many urban communities and institutions, finding new and innovative ways of growing food in cities has become increasingly important in order to expand sustainability and resilience of local food systems, especially in the face of climate change. Our study was conducted to assess the potential benefits of rooftop gardening, an emerging form of urban agriculture, to the University of Wisconsin-Madison, as well as provide recommendations for best practices to guide implementation of such a project. Research focused on evaluating the capacity of a rooftop garden on Union South to supply leafy greens- lettuce, romaine, arugula, and spinach- to the campus dining facilities. Based on our literature review, interviews with key stakeholders on campus, and case studies of comparable universities with rooftop gardens, it was determined that an estimated 10% of Union Dining’s leafy green supply per month, or 179 pounds, can be seasonally provided by converting 2,297 square feet of Union South’s rooftop, or 30% of the existing 7,853 square feet of extensive green roof, to agricultural use (CPD 2015). This pilot project would provide Union Dining Services with leafy greens from late May to early October, and could serve as a model and a catalyst for future green roof design on new and existing UW buildings. This type of initiative would help demonstrate the university’s commitment to sustainability by better utilizing space, promoting energy efficiency, reducing stormwater runoff, and contributing to a more resilient local food economy.

Introduction

Cities consume around ¾ of the world’s resources, and with growing populations and climate change putting increasing pressure on food systems, the quest to diversify food production and enhance sustainability has taken a more vital role both locally and globally (Thomaier et. al 2014). As the world becomes increasingly urbanized, the need exists for an integration of food production into urban areas in order to increase food security and support cultural traditions (FAO 2016). Urban agriculture, as defined by the Urban Agriculture Committee of the CFSC (2003), is “the growing, processing, and distribution of food and other products through intensive plant cultivation and animal husbandry in and around cities.” While not necessarily a new concept, this mode of localized food production has come under increasing application, development, and diversification in recent years to adapt to urban landscapes in new and creative ways. In response to challenges such as land scarcity, soil contamination, and high costs of city lots, urban gardeners have developed methods such as intensive square-foot container gardening, vertical “window farming” and “guerilla gardening”, in which edible plants are grown in areas unintended for garden use (Certoma 2011).

Another inventive method of urban agriculture is rooftop gardening. Historically, this practice can be seen as far back as the terraced ziggurats of Mesopotamia (Allhoff and O’Brien 2011). Today, rooftop gardens are appearing in cities around the world, from New York, Chicago, and Toronto in North America, to Tokyo and Hong Kong in Asia (Thomaier et al 2015), Bologna and Manchester in Europe (Orsini et al 2015; Castleton et. al 2010), and Durban in Africa (Dubbeling & Massonneau 2014), just to name a few. Rooftop gardening carries several unique benefits as a form of urban agriculture, such as increased access to sunlight, reduced exposure to urban pests and heavy metal runoff from roads, and a decreased likelihood of vandalism (Whittinghill and Rowe 2012).

Sustainability initiatives on many campuses across the U.S. have led to the implementation of urban agricultural operations, including rooftop gardens. At the University of Wisconsin-Madison, the leading organization for urban agriculture activities is the F.H. King Students for Sustainable Agriculture. Students within this program maintain a rooftop greenhouse on the Aldo Leopold Residence Hall and a raised-bed garden on the roof of the Pyle Center (Leopold Residence Hall Website 2016; F.H. King Website 2016). Additionally, UW-Madison has installed several green roof systems on campus to mitigate stormwater runoff into the lakes and reduce building heat fluctuations. These green roofs are extensive systems, composed of low-maintenance ornamental sedum plants that require little substrate (Getter & Rowe 2006).

The sustainability vision of the UW-Madison campus, which emphasizes “environmental, economic and social responsibility to people and the planet” (Office of Sustainability 2016), can be further fulfilled by expanding rooftop garden practices in order to supply food to Union Dining Services. Therefore, the main goals of our project was to promote and recommend best practices for implementing more rooftop gardens on the UW-Madison campus. Through our research and analysis, we sought to answer the following questions:

Literature Review

In order to better understand how rooftop gardens can benefit our campus and promote environmental, economic, and social sustainability, we performed a meta-analysis of existing literature on rooftop gardens and urban agriculture systems more generally. Rooftop gardens have been proven to provide an abundance of services to local food systems, and contribute to the sustainability and security not only of the building itself, but to the surrounding community and environment and the broader global climate as a whole. The results of this literature review provide a strong argument for establishing a rooftop garden on Union South, as well as pursuing other urban agricultural initiatives on the UW-Madison Campus.

Rooftop gardens provide numerous ecological benefits to urban areas and to the local and global environment as a whole. In most urban centers, the surfaces of roofs, roads, and other areas are primarily made up of non-porous material such as asphalt. This results in the runoff of stormwater, heavy metals, nutrients, and other hazardous chemicals, into local bodies of water, which causes contamination of water and eutrophication (Paul & Meyer 2001). Rooftop gardens, being established in a soil substrate, provide a porous material that absorbs rainwater landing on buildings. Studies have shown that lined green roof systems can reduce stormwater runoff by 50-70% (Bliss et al 2008; Blackhurst et al 2010; Richard 2015). As UW-Madison is located in close proximity to lakes Monona and Mendota, preventing runoff from campus into these lakes is an essential part of our campus’ environmental sustainability.

In addition to mitigating stormwater runoff, rooftop gardens can reduce the urban heat island effect of cities. The solar absorptive properties of many urban road and rooftop materials, which then radiate heat, causes urban areas to be on average 5-15 degrees Celsius warmer than rural areas (Dubbeling et al 2014). Rooftop plants provide a more reflective coverage of roofs, maintaining a lower overall roof temperature and reducing cooling costs during the summer months. The insulative effects of the soil substrate can also lower building heating costs during the winter. The degree of these energy savings depends on the amount of vegetative coverage, local climate, and type of building heating/cooling system. However, the overall benefits of a rooftop garden system can reduce the energy demands and therefore environmental footprint of the building and help lower the overall temperature of urban areas (Dubbeling et al 2014). Rooftops with thicker substrate, such as those provided through intensive rooftop gardens, have been shown to perform better in an environmental LCA than extensive green roof system (Kosareo & Ries 2007). On a campus as widespread and with as many buildings as UW-Madison, rooftop gardens and green roofs could have a significant impact in reducing the campus’ energy consumption and environmental impact.

A large portion of produce grown in the United States, including 70% of the nation’s spinach and lettuce, is grown in California (USDA Economic Resource Services 2015). This results in greater costs and greenhouse gas (GHG) emissions from transporting the produce from producers in California to retailers and consumers here in Wisconsin. This distance is referred to as “food miles.” The production of food locally, such as through urban agricultural systems, can greatly reduce the number of food miles associated with different produce (Pirog et al 2001). Weber and Matthews (2008) argue that, in the overall scheme of food systems, GHG emissions from food transportation are relatively minimal compared to emissions from the on-farm production of the food. However, their study did not account for additional environmental costs associated with transporting food over long distances, such as processing and packaging. In addition, California’s agricultural production has come under increasing pressure from droughts, which threaten the irrigation systems that the majority of their crops depend on (Hayoe et al 2004). Therefor, rooftop gardens and other forms of local food production can help regionalize food systems and move production away from more environmentally sensitive areas such as California (Lengnik et al 2010). Diversification of agriculture, including the expansion of urban agricultural production, can also promote food stability in the face of more extreme weather events that result from climate change (Paci-Green & Berardi 2015). Local production also exposes members of the community to more opportunities to obtain fresh produce, which has shown to promote a shift away from red meat consumption, which has a very high environmental footprint (Landis et al 2010). While the UW-Madison campus would not be able to produce 100% of its leafy greens year round through urban agriculture, local seasonal production would reduce the campus’ environmental impact and increase its food security by reducing food miles and pressure on California’s sensitive ecosystem.

Urban centers can often serve to degrade and fragment the habitats of local species. In this sense, rooftop gardens and green roofs can provide “ecological corridors” for birds, pollinators, and other insects both in and through urban areas (Orsini 2014; Vergnes 2014). A study conducted in Durban, South Africa showed that, in comparing a bare roof to a comparable roof with a garden, the rooftop garden contained 100x more insects, showing the effectiveness of rooftop gardens in supporting biodiversity (Dubbeling et al 2014).

Rooftop gardens provide numerous cost benefits to the buildings that they are built on, as well as through savings accrued by growing food locally. As mentioned before, green roofs can help provide roof cooling in the summer and insulation in the winter. These net energy savings have been demonstrated in several green roof studies using different metrics:

While these studies provide strong evidence for the building energy savings provided by a green roof system, the results were obtained in specific contexts (climate, building type, green roof properties), and are therefore difficult to apply to predict the exact energy savings of a green roof project.

Although green roofs can be two to six times more expensive to install than conventional roof systems (Whittinghill & Rowe 2012), studies show that green roofs can actually provide net savings in the long run (Peck & Callaghan 1999; Wong 2003; GSA 2011). Beyond savings accrued through decreased energy costs, green roofs increase the lifespan of roofs and reduce maintenance or replacement costs by protecting the structure from severe weather and wind (Peck & Callaghan 1999). A study by GSA (2011) estimated that buildings with a green roof last on average forty years, compared to just seventeen years for the average conventional roof. The longevity of green roofs is the largest contributor to cost savings for the building operator (GSA 2011). The greatest net-benefit in energy savings from green roofs occurs on older buildings, which tend to have less built-in insulation (Castleton et al 2010). These buildings might not have the weight bearing capacity to support an intensive rooftop garden, and would be better suited for extensive green roofing. Rooftop gardens are especially cost effective on multifamily and commercial facilities when the social benefits are taken into account (Blackhurst et al 2010). Green roofs on current and future buildings at UW-Madison would increase the campus’ economic sustainability both in the short and long term.

Rooftop gardens contribute to social sustainability and local food systems by providing increased food security and access to better nutrition. For most urban food systems that are highly dependent on external food sources, rooftop gardens and urban agriculture can provide a sense of food security and empowerment (FAO 2015). In addition, rooftop gardens that have high yields and follow Good Agricultural Practice (GAP) food safety guidelines may serve as a valuable source of income for individuals who choose to sell their produce (Whittinghill & Rowe 2012). Local produce sources also increase the consistency with which people consume fruits and vegetables. A study by Alaimo et al (2008) found that adults with a household member who participated in a community garden consumed fruits and vegetables 1.4 times more per day than those who did not participate, and were 3.5 times more likely to consume fruits and vegetables at least five times a day. By providing a local food source that students at UW-Madison’s campus can get involved in, campus rooftop gardens could contribute to better dietary practices among students and staff and promote greater involvement in the local food system.

For the UW-Madison campus, rooftop gardens would be an invaluable source of education and research for students in departments such as agriculture, urban and regional planning, and environmental studies. For universities, sustainable food projects are an impactful way to retain more students by offering many the chance to build deeper community connections and gain hands-on experience in sustainable farming (Barlett 2011; Gardner 2012). Concern for the environment has also become an increasingly important factor for many prospective students when choosing a campus. A recent survey of incoming freshmen in the U.S. by the Princeton Review (2016), found that 61% of students surveyed said that having information about colleges’ commitment to environmental issues would contribute “strongly”, “very much”, or “somewhat” to their application/attendance decisions. Currently at UW-Madison, the F.H. King Students for Sustainable Agriculture conduct many outreach programs to the larger campus community, including free rooftop gardening classes and the distribution of free produce to students during the growing season. More rooftop gardens at UW-Madison would not only attract more prospective students, but also contribute to furthering the educational and research opportunities of UW students and the campus as a whole.

As shown by our meta-analysis above, rooftop gardening on the UW-Madison campus would provide numerous environmental, economic, and social benefits to members of the campus, the local community, and local and global ecosystems. Leafy green production on Union South’s rooftop for student consumption was chosen as a pilot idea for future urban farming initiatives on the UW-Madison campus. This was based on pre-existing research done by Silva et al., who conducted water quality assessments and leafy green yield trials on different growing media, proposed potential green roof sites on the UW campus, and explored the potential to produce leafy greens on Union South’s rooftop for Union Dining services on campus. From our literature review and this study, we derived the following hypotheses:

Materials and Methods

The boundary of our research was geographically defined as rooftop food production on the University of Wisconsin-Madison campus, specifically the Union South building. Our objective was to estimate the volume (pounds) of marketable leafy greens could be produced annually from a rooftop garden to be used in Union Dining facilities. Additionally we sought to understand the potential impact a rooftop garden would have on the environmental, economic, and social sustainability of UW-Madison. Methods included discussion with key stakeholders on campus, a literary review of related research, and inclusion of primary research conducted to understand operational aspects of rooftop gardens in other university settings.

The focus of the literature review was placed on qualitative and quantitative analysis of the three main pillars of sustainability with respect to green roofs, as well as an analysis of case studies outlining design considerations and productivity of rooftop farming operations. When possible, publications were selected that had comparable conditions as UW-Madison. Meetings and conversations with Cathy Middlecamp, the interim dean of UW-Madison’s Office of Sustainability, as well as Tom Bryan, a PhD candidate through the Nelson Institute for Environmental studies, was instrumental in helping the team understand the history of sustainability efforts on campus and guide our analysis of rooftop gardens. Communications with Frank Laufenberg from F.H. King about rooftop production on the Pyle Center provided us with information about local growing conditions and production potential here in Madison. Carl Korz, the Director of Union Dining Services, was contacted as well, and provided us with information on the amount of leafy greens used by Union Dining Services on an annual basis (Union Dining Services includes Union South, Memorial Union, and Grab n’ Go Kitchens on campus).

To understand objectives, design, and complications of implementation of other University affiliated rooftop gardens, the team conducted qualitative phone interviews with managers of rooftop gardens at four universities. The universities were selected for similarities with UW-Madison, including size, relative geographic location, and land grant status. Universities included were the University of Maryland, the University of Wisconsin-Milwaukee, the University of the District of Columbia, and Michigan State University. A standardized list of questions was developed and data was recorded during the conversations, which each lasted approximately 30-minutes.

In order to estimate the potential yield per square feet that we could achieve on a rooftop setting on the UW-Madison Campus, we utilized data from a report by Erin Silva et al (2014), which presented the results of yield and water quality study of five different growing media types for a leafy green mix on the UW Pyle Center rooftop.The plants were grown in plexiglass planting boxes with drains to collect effluent water, which was tested for N and P content (nutrient runoff) and coliform bacteria concentration (food safety). It was concluded through this study that Rooflite Intensive growing media is the best for UWs purposes in growing leafy greens with a yield of 7.8 lbs/100 square feet, as well as lower nutrient concentration, and relatively low bacterial loads in the effluent water. This study also estimated that a minimum of $135,000 would be necessary to fund an initial structural engineering analysis, full cost/benefit analysis, and life-cycle analysis of the space, with additional research on the roof manufacturer’s warranty that would have to be upheld in the practice. Additional research on Union South’s existing extensive green roof structure was conducted through the university’s Capital Planning & Development Website to estimate the potential space on Union South’s roof that could be converted to edible leafy green production. Using the information above, as well as information on Union Dining leafy green consumption provided by Carl Corz, we formulated an estimate of how much of Union South’s leafy green production could be provided by semi-intensive rooftop gardening during a late May through early October growing period (see Results and Discussion).

Limitations

The study relied heavily on availability and scope of data on green roof gardens, as well as the degree of comparability to conditions in Madison, WI. Challenges arose in finding the necessary data to estimate potential rooftop yields/sq ft of specific leafy greens and understand procurement patterns and quantities of leafy greens at Union South specifically (versus all of Union Dining Services). Due to variations across climates and building designs, as well as costs of resources and labor, there was difficulty generalizing economic and environmental impacts across case studies. Difficulty in contacting certain key players on campus limited the extent to which we could solidify our estimates for production on Union South. For instance, communication issues with Union South’s building manager limited our ability to better estimate the square footage we could utilize on Union South for intensive rooftop agriculture. Finally, the condensed timeline and limited capacity of the research team dictated the extent to which we could explore topics of interest and implement further research (such as yield trials on Union South specifically).

Results and Discussion

These case studies are instructive for UW-Madison’s rooftop garden project in many ways. A key takeaway was that successful, sustainable projects are built on strong partnerships between dining services staff, students, professors, and administrators. Although student interest wasn't a problem at the University of Maryland (UMD), they had weak relations between students and staff which resulted in disruptions in the community project. Another takeaway is that there needs to be proper facilities that are able to manage an intensive rooftop garden system that provides additional benefits. UMD didn’t have enough soil coverage to take advantage of the environmental and cost benefits like stormwater mitigation. University of the District of Columbia and UW-Milwaukee (UWM) had issues with accessing the volume of water necessary for rooftop agricultural production.

Both MSU and UWM integrated the school dining services into their projects which kept their supply costs down while increasing the quality and freshness of food served. If UW-Madison aims to maximally capitalize on all three pillars of sustainability, it will need to invest in the project accordingly by learning from other green roof production systems, taking the time to plan and implement systems that will meet the needs of the UW campus. In addition to structural planning and relationships to facilities and students, the case study results also suggest that university researchers should be able to access the rooftop garden for innovative research in urban agriculture. As the number of rooftops used for agriculture increase across the U.S. and beyond, more research needs to be conducted on the particular issues and opportunities that come with growing food on buildings. A reputable land grant institution, UW-Madison should be serving as a leader in this burgeoning field of research, and the investment in piloting a rooftop agricultural research station would be a necessary first step.

Union South Yield Estimates

The Union South building currently has 7,853 sq ft in extensive green roof production, with an additional 48,284 sq ft of high albedo roof surface to reflect sunlight (CPD 2015). A portion of the water from the roof is collected and used in a water feature next to the building. Due to these factors, and the building’s Gold LEED certification rating, it may not garner the greatest net economic benefits of green roof infrastructure versus an older building. The preexisting extensive green roof infrastructure, however, makes Union South a good location for an initial pilot garden. Based on the information gained from our research and the yield estimates from Silva et al, if UW-Madison were to cultivate edible leafy greens on 2,297 square feet of Union South’s rooftop (~30% of the existing green roof), it could supply roughly 179 pounds of leafy greens per month to the Union Dining Services. As Union Dining uses an average of 2,060 pounds of leafy greens per month, this would cover approximately 10% of the Union’s leafy greens from late May to early October. This garden would benefit the campus in multiple ways, such as engaging more students in the campus food system, providing new research opportunities, increasing the campus’ food security, and reducing economic costs to Union South and University Dining Services.

Union Dining *annual leafy green consumption. Numbers obtained from Carl Korz.

Summary and Conclusion

Taking into consideration recommendations from the team’s research, as well as those gathered through the feasibility analysis performed by Silva et al (2014), UW-Madison has the opportunity to become a leader in university affiliated rooftop farming initiatives. The adoption of rooftop farming practices on campus would demonstrate a commitment to environmental, social, and economic sustainability. It is crucial that, before implementation, key stakeholders from a variety of places within the university (administration, faculty, student groups, dining service, etc.) express commitments to advancing the project further. Additionally, more data would be needed to understand the university’s volume of demand during the summer, and the best avenues for incorporation into the school’s dining services should be identified. Metrics more specific to Union South’s leafy green demand would also assist in making more accurate predictions as to the percent of leafy greens that could be provided for Union South versus Union Dining as a whole. A pilot program on Union South, where 7,853 sq ft of extensive green roof infrastructure is already in place, could help to guide future design considerations. Further exploration of suitable building sites on campus that might garner larger benefits from green roof features should be performed to inform the future of rooftop gardens and extensive green roof infrastructure at UW-Madison. Although rooftop gardening is limited to seasonal production, and will not grow all of the food needed to maintain Union South’s dining services, it is a strategy that will help make the campus food chain more energy efficient, more connected to the community, and more resilient in the face of climate change.

Rooftop gardening is not the only form of urban agriculture that has the potential to improve the sustainability of UW-Madison’s supply chain. Urban farming projects demonstrate an array of methodology, such as re-purposed ground plots in vacant lots and controlled environment agriculture, such as hydroponics and aquaponics. To help guide future research, a project snapshot was created to help researchers or other stakeholders understand the plausibility of an alternative urban farming method- aquaponics. This method was chosen due to Wisconsin’s reputation as a leader in the aquaponics industry, as well as the University’s proximity to a global leader in aquaponics technology and systems design. The UW System at UW-Steven’s Point is already partnered with Wisconsin’s aquaponics industry through Nelson & Pade, Inc., where they collaborate through research and education.

Future research should be conducted to understand, compare, and contrast different urban farming methods, and the potential for food production, sustainability, research and education that could be achieved with their implementation at the University of Wisconsin-Madison. Implementing a rooftop garden on Union South would be a vital first step in improving the sustainability of our campus as a whole for both present and future generations of UW-Madison students.

Research Team

Katie Cyr - Biology; Environmental Studies (Senior)

Joe Elliott - Agronomy; Environmental Studies (Senior)

Emily Twohig - Biology; South East Asian Studies (Senior)

Marlie Wilson - Agroecology; Urban & Regional Planning (Graduate)

Works Cited