St. Mary’s cultivates a greener city

SMU Green Roof

HALIFAX – While urban spaces are being rethought across the country, Halifax’s own St. Mary’s University is leading the way in the Maritimes. As it stands now, there is only so much room for green space in our urban environment. Think about it: industrial sectors, vast networks of paved streets and highways, swaths of residential neighborhoods and commercial districts make up the edifice of the modern city, and this built environment has in large part succeeded in separating us from nature.

To be sure, we’re getting better at reversing this trend. The green building movement is gaining momentum and city planners and developers are – albeit slowly – becoming increasingly cognizant of the need to incorporate more of the natural into our built environments.

Green spaces, though, are not mere city frills; they need to be thought of, rather, as necessities of urban space in the same vein as schools and public transportation. Beyond the touted restorative powers of nature, parks provide many other benefits to a city, including ecological biodiversity and natural temperature regulation. However, as long as green spaces are confined to the areas between buildings these benefits will be scarcely felt.

Unused space atop every building affords a rare chance to bring a little more nature into the concrete jungle while simultaneously providing important ecological services in urban areas. If legislation recently passed in Toronto and currently being considered in Vancouver and Ottawa is any indication, green roofs will soon become much more prevalent in our cities.

More specifically, St. Mary’s University is currently exploring the economic and enviromental viability of applying green roof technology in Halifax, both in terms of new construction projects and retrofitting existing buildings.

There are two basic types of green roofs: intensive and extensive. The differences between the two lie mostly in the desired function of the roof space, necessitating different soil depths to accommodate the various plants, shrubs and trees planted. Intensive roof systems have a relatively deep growing medium able to support nearly any vegetation desired and are often used as recreational areas. By contrast, extensive roof systems have a much more shallow growing medium but are generally more self-sustaining, requiring much less maintenance.

Dr. Jeremy Lundholm, professor of Biology and Environmental Studies at St. Mary’s University, is currently testing the adaptability of green roofs to the specific maritime environment of Halifax. The legislation recently passed in Toronto, requiring all buildings constructed after January 31, 2010 to dedicate an amount of green roof space proportional to their size, was enacted in part to combat the urban heat island affect. Toronto’s temperature rises each summer as the city’s surfaces – asphalt, concrete and the like – absorb heat. The application of green roof technology in Halifax, on the other hand, is multipurpose in its aims. It is concerned with reversing the direction of heat flow in the winter (thus reducing energy consumption through thermal moderation), storm-water management and retention, reducing storm-water runoff that can denigrate water quality, and the provision of habitat and pollination grounds for local wildlife and flora.

Faced with these unique problems, Dr. Lundholm has been required to come up with equally unique solutions, inducing his attempts to utilize local plants. Most green roofs cultivate a monoculture – that is, a single crop – according to the calculus of economic benefits, often importing foreign vegetation to do so. This process is, in effect, like grafting an European ecosystem into North American conditions, thereby ignoring both the benefit of biodiversity and local vegetation.

Dr. Lundholm’s lab is studying the performance of native plant species and the role of intermingling flora on green roofs in Atlantic Canada. He has tried to mirror the local environment, choosing plants that are well adapted to the particular climate facing plants in Halifax. These homegrown solutions will lead to an increase in native biodiversity and will also create demand amongst local growers.

The end result, he says, is to get more green roofs built in Atlantic Canada. The environmental debate has traditionally been framed as a clash between economic progress and sustainability; the goal of projects like Dr. Lundholms, then, is proving the economic and environmental incentives of green roof technology, spurring government stimulus and regulations mandating efficient building technologies.

There are certainly templates Halifax can follow: Toronto’s legislation on green roofs for large residential, commercial and industrial buildings is one example, while many cities in the United States require building owners to manage stormwater that is diverted from their impervious surfaces, with green roofs promoted as viable solutions to these problems.

The big picture is the creation of restorative buildings – buildings that give back in terms of renewable energy, clean air and water and green space.  Green roofs that utilize local flora while creating habitat for local fauna and simultaneously reduce the ecological footprint of our urban space is certainly a step in the right direction.

photo by Jesse Mintz


  1. Interesting thoughts on what might perhaps be regarded as a minor achievement in Canada’s heretofore embarrassing ecological considerations, but in the bigger picture is perhaps the exact kind of movement we need. Raise the Roof.

  2. Interesting insights indeed. I will say, though, that the photograph does not quite match the eloquence of the explanation. I conjured an image of a rich, green environment that looked more like a greenhouse – it looks more like a poorly maintained Scarborough backlot. Though I support green roofs in any context I can, maybe I have always romanticized the notion. Are they really not more esthetically pleasing?

    Either way, with these exciting precedents being set and environmental issues moving towards the front-burner, I’m all for as much greening as possible…Except for the schoolyards, they need to stay concrete.

  3. The photo is of our modular experimental set-up which we use to assess several properties of individual plant species or mixtures, and in no way looks like an installed green roof! There are plenty of nice ones out there! Just Google image!

    The more species we can prove work in the region, the more diverse (and potentially higher performing) our green roofs will be. Increasing urban biodiversity (and vegetated surface area) increases ecosystem resilience and a whole host of other services in cities.

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