Rooftop Farms

Initiatives are growing to have building roofs become urban farms.

Environmental degradation, urban sprawl, waning water resources, increase in population, and dependence on imports are all factors putting significant pressure on the food supply. Urban rooftop farming, pioneered by local food and sustainable agriculture movements, has developed to alleviate some of that pressure.

The rooftop farming trend is more prominent in the U.S., where many municipalities have responded with favourable bylaw and zoning amendments to create urban agricultural districts and permit farming in residential zones. Brooklyn Grange operates the world's largest rooftop soil farms located on two roofs in New York City operating under 10 and 20 year leases. One of the farms is 43,000 square feet containing approximately 1.2 million lbs. of soil. Brooklyn Grange grows over 50,000 lbs. of produce per year.

Canadian municipalities are beginning to respond to the growing demand for urban agriculture and rooftop farming. The City of Edmonton's "fresh: Urban Food and Agriculture Strategy" (October 2012) identified rooftop gardens in the inner urban area as an opportunity for food production and recommended that the municipality assess regulatory barriers for green roofs.

In November 2013, Toronto City Council adopted the Toronto Agricultural Program, which included the Urban Agricultural Workplan. A component of the plan is promoting urban agriculture on rooftops through the Eco-Roof Incentive Program. Toronto also has a Green Roof Bylaw requiring green roofs on new commercial, institutional and residential developments with a minimum gross floor area of 2,000 square metres, to be built in accordance with the Toronto Green Roof Construction Standard (Toronto Municipal Code, Chapter 492, Green Roofs).

Similarly, a Green Roof Bylaw in Port Coquitlam, B.C. requires new commercial or industrial use buildings having a building area of 5,000 square metres or more to have a green roof on at least 75 per cent of the roof area (Zoning Bylaw, 2008, No 3630, s 12.1).

Zoning and bylaws, including green roof bylaws in most Canadian municipalities, are not specific to rooftop farming.

However, the absence of such specificity has not prevented the establishment of urban rooftop farms across Canada. To name a few: Lufa Farms has a 31,000 sq.ft. rooftop greenhouse in Montreal (www.lufa.com). In Vancouver, the downtown YWCA Metro Vancouver has a rooftop food garden which had a harvest of 720 kilograms in 2012 (www.ymcavan.org).

In terms of opportunities, rooftops represent an abundant farming resource in dense urban areas. Rooftop farms reduce greenhouse gas emissions by reducing transportation costs and environmental impacts. They allow the absorption of stormwater which reduces the strain on drainage systems, and they cool urban air temperatures.

Rooftop farming also supports local businesses and the local food supply industry. It creates sustainable and economic opportunities for repurposing unused spaces, lends itself to creative leasing arrangements and is a natural progression for the design and construction of green buildings.

Consequently, municipalities should expand their efforts to accommodate rooftop farming. Doing so would counter public concern over the decreasing areas of green space.

Engineers who may become involved in designing rooftop farms should consider the following:

• municipal plans, bylaws and strategies for urban agriculture;
• municipal zoning and permits
• municipal laws for pesticides, fertilizers, water contamination, landscaping and noise pollution
• existing building integrity including structural capacity, access and drainage
• building code specifications for structural integrity and requirements for plans and drawings
• weight capacity including for soil, vegetation, irrigation and equipment with allowances for seasonal impact
• sufficiency of the waste management system
• insurance requirements and allocation of risk in leasing agreements
• incentive programs and tax benefits.

While the concept of rooftop farming is relatively novel, it stands to become more prevalent, providing an excellent opportunity for cutting-edge engineers to be proactive and to contribute to urban initiatives.

Originally published by Canadian Consulting Engineer, August/September 2014.

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