Nature on Top

Rooftop greenery

November 26, 2009 – Scott MacIvor is a postgraduate student at St. Mary’s University in Halifax, who is researching green roofs, an exciting technology that increases the sustainability of urban centres by bringing nature downtown. Many green roofs are planted with non-native species that can withstand the harsh rooftop conditions, but are optimized to perform only a select number of ecosystem functions. MacIvor’s research aims to identify the value of native plants to green roofs. He hypothesizes that using local plant life may enhance the performance and ecological services of green roofs.

Green roofs provide many benefits for buildings and reduce the impact that cities have on the environment. Urban centres are an average of four degrees Celsius warmer than surrounding areas because traditional building materials absorb the sun’s rays and release them as heat. A collection of green roofs can regulate a city’s temperature by reflecting these rays while providing an insulating barrier that maintains temperatures within a building. Green roofs keep buildings cooler in the summer and warmer in the winter, yielding up to 26 percent reduction in energy needs. They also reduce storm water run-off, retaining up to 75 percent of the water and trapping pollutants in their soil. Finally, in terms of economic benefit, they have been shown to increase a roof’s life span by up to three times.

MacIvor is conducting his research at the Green Roof Testing Facility at St. Mary’s University, using up to 15 native species in replicated modules. Over the course of one year, he is tracking growth rates, cover, reflectivity, soil temperature, water retention and survivorship. These results will then be compared with the performance of three non-native plant species that are commonly used in the industry. His goal is to expand the number of plants for viable use in the Canadian green roof industry.

Another important aspect being monitored is insect biodiversity. While the prospect of more bugs may not appeal to everyone, they are integral members of the ecosystem. The health of a green roof can, to a large extent, be measured by the prominence and selection of the insects inhabiting it. The diversity and strength of the insect population will be compared against those found in ground-level city vegetation.

MacIvor points out that green roofs could provide solutions to several urban problems. Rooftop gardens provide habitats for wildlife within the city and could make urban areas more animal-friendly and reinforce populations. The same can be said for the flora used. MacIvor sees green roofs as an opportunity for plant conservation. For his research, he is using coastal barren plant species, some of which are rare or endangered. If these plants prove to be well-suited to the exposure of a rooftop environment, they could become widely adopted by the green roof industry and increase their cultivation.

Green roofs have received considerable popularity in Europe, where they first emerged in the late 1960s. While North America has been slow to adopt this technology, there has been an increased uptake in the last few years, particularly in large cities. Chicago is leading the way with more than 200 green roofs and a grant program to encourage its adoption. The city of Toronto approved a by-law in May of 2009 that will require industrial buildings to have 10 percent of their roofs greened by 2011.

MacIvor’s research into the viability of native plants could provide a template for future studies that would further expand the knowledge of regional plant use and broaden the applicability of green roof technology. By greening up our city rooftops, everyone and everything, from bugs to businesses, stand to benefit.