OOS 10-5 - Green roof technology in urban agriculture: lessons learned in the last decade

Background/Question/Methods
As green roofs have become more popular in North America, there has also been growing interest in using green roof technology to grow food on rooftops. There have been a number of publications suggesting that this could be an important component of sustainable development in cities moving forward that would also address food insecurity. Many of publications brought up potential issues that might prevent green roof agriculture form reaching its potential. These include a) the compatibility crop vegetables with green roofs, in particular the shallow green roofs that would be necessary on most retrofitted buildings; b) how the use of compost and additional fertilizers affect runoff water quality compared to ornamental green roofs; c) how the use of irrigation affects stormwater management compared to ornamental green roofs; d) how the rooftop environment affects management practices including nutrient and irrigation recommendations; and e) if sufficient yields can be achieved to impact food insecurity in a city. A review of literature was conducted to determine if these, and other issues raised by the early articles have been sufficiently addressed and to determine what the next steps for research might be.

Results/Conclusions
Just over 25% of the peer review articles on rooftop agriculture using green roof technology published since 2012 continue to explore the sustainability and utility of rooftop farming. These papers reiterate some of the previously noted concerns. Those that take an analytical approach suggest that while rooftop agriculture using green roof technology may have its benefits, it may not be competitive when compared with alternatives such as rooftop hydroponics in greenhouses. Less than fifty peer review publications have examined rooftop agriculture using green roof technology through small scale experimentation, monitoring on rooftop farms, and surveys of existing rooftop farms. In many ways these experiments are still exploratory, though some directly address concerns noted in earlier research about stormwater retention, stormwater runoff quality, and the potential for heavy metal contamination. Despite relatively little scientific progress on issues related to rooftop agriculture using green roof technology, the number of such roofs has continued to increase. In most cases, these roofs also continue to use intensive green roof systems with substrates usually 20 cm deep or deeper. This practice seems to contradict the concern that roof load capacity restrict agriculture to extensive systems if it is to be implemented on a wider scale.