Although the benefits of rooftop agriculture highlight the importance of bridging infrastructure and food systems, there are still some drawbacks that must be considered.
In an interview with Chris Grallert, President of Green City Growers, some of these drawbacks were discussed. Green City Growers is a U.S. based company that helps other companies to set up their own urban greenspaces. Recently, Green City Growers has even established a rooftop green space on Fenway Park in Boston, MA.
Material Cost
The main concern with shifting towards rooftop systems such as hydroponics or greenhouses is the cost of material. According to Grallert, “hydroponic systems like these are high value, they’re also expensive at retail so not every demographic currently. And also the sustainability around it, a lot of glass and concrete and steel to build these. The life cycle analysis is still out on that as well.” He’s not alone in this concern; in a 2021 assessment of urban greenhouses, it was found that “One of the key elements for greenhouse building-integrated agriculture (BIA) and conventional agriculture (CA) to achieve high levels of environmental performance is their structural design, which largely impacts the economic and environmental life-cycle costs (by up to 63%). “ The concern regarding material cost is legitimate. The point of rooftop agriculture is to create not only sustainable food systems, but accessible ones as well. In fact, one of the key components of just sustainability is equity, and ensuring that the systems in place promote quality food to everyone, not just those with disposable income.
In order to help curb this concern, flexible structures with membrane solutions are beginning to be popularized by structural designers, to mitigate the construction cost of rigid structures. One such optimization can be seen in the following diagram:
taken from: https://doi.org/10.1016/j.resconrec.2021.105526
Building Codes
Another key challenge regarding rooftop gardens (RTGs) is finding the right rooftops. In order to accommodate the necessary systems for largescale RTGs, roofs must be able to support the weight, drainage, and safety of the agricultural system — among other considerations. In regards to this challenge, Grallert added that “There are certain integral requirements that a structure needs to have to be able to hold the extra weight, to have the sensibility and safety up on a roof, and accomodate things like water, and ability to process the crop after it’s harvested… it’s very challenging to generate a profit on the vegetables to pay for the operation until we start to integrate some of the environmental and social benefits into the cost and the pricing.”
One solution is turning specifically to industrial and logistic parks, which are able to support commercial RTGs due to their larger size, strong structure, ownership, and shape. The potential reduction of heating and cooling requirements compared to residential buildings is also an improvement. Although this is not ideal for inner-city implementation, it is still an opportunity worth investigating.
Energy Use
Energy use is actually a pro-RTG consideration, due to the fact that RTGs can lead to energy savings in heating and cooling demands compared to conventional greenhouses. This means that once the systems are installed and running, there is eventually a return on investment in the form of energy. In order to properly integrate these systems, there must be both environmental and economic draws. Energy is one such benefit.
A table summarizing these pros and cons can be seen below.
Table 1. SWOT analysis of RTGs, from Drottberger, et. al
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Strengths
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Weaknesses
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Opportunities
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Threats
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