If more than the myth some scholars call it, the first green roof was built by the king of the ancient city-state of Babylon – about 85 kilometres south of modern-day Baghdad – in 600 BC. He built it atop the terraced palace for his wife, who missed the greenery of her homeland, in what’s now Iran.

Greek historians called the Hanging Gardens of Babylon one of the seven wonders of their world. Their accounts, however, seem less taken with the purported beauty of the project than with its ingenuity in bringing nature to the city in such an extraordinary way.

Dr. Leonie Nadeau isn’t trying to transform the greater Edmonton region into a new Babylon, but she would certainly like to see more plant life in the built landscape of what’s already one of Canada’s greenest cities. Right now, that’s a challenge.

“There is not enough data for our climatic conditions,” says the retired NAIT senior researcher. To rectify that, she has spent the last year amassing information necessary to help more businesses and organizations sow the seeds of a living skyline.

Benefits and challenges of green roofs

In “Green Roofs in Urban Ecosystems (5.14 MB PDF),” a 2007 Digital Commons @ Ryerson article, authors Erica Oberndorfer et al. suggest rooftop gardening addresses the issue of how “Buildings change the flow of energy and matter through urban ecosystems, often causing environmental problems.”

In other words, city structures displace nature, which, especially if the lush and leafy kind, manages storm water, provides wildlife habitat, lowers temperature and more.

To an extent, green roofs can do the same, say the authors, while also providing building insulation and increasing the lifespan of a roof.

Establishing one, however, can be challenging, taking about three years. What’s more, says Nadeau, it can be expensive, given the materials and possible requirement of reinforcing a roof to accommodate the plants and growth media.

Besides that, conditions can be harsh. The average Edmonton rooftop sees the extremes of each season. In winter, greater exposure to wind can mean colder conditions. In summer, surrounding buildings can amplify the intensity of the heat.

Nevertheless, what Nadeau has seen so far on existing green roofs in Edmonton makes her optimistic that a time may come when such ecosystems are common in the capital. “The important thing,” she says, “is to get more green spaces in any area.”

Early research results

By June, 2010, the roof of Williams Engineering Canada Inc., overlooking Edmonton’s river valley (and pictured above), was converted to a rooftop garden.

Alberta Real Estate Foundation provided initial funding for the project while Native Plant Producers Society of Alberta provided seedlings that included 17 species of grasses and flowering plants (or forbs) including sage, aster and flax native to southeastern Alberta, one of the harshest environments in the province.

In addition, several suppliers discounted (or even donated) materials for the project, which had the full support of Tonko Realty Advisors Ltd., property manager of the building.

Nadeau led a team of students from NAIT’s Bachelor of Technology in Technology Management and Landscape Architectural Technology programs through the project, along with a group from H.P. Wagner High School. Some were involved in the roof's design, and some investigated growth in three depths of a mix of mostly compost and peat moss: 7.5, 10 and 15 centimetres. Expectedly, she reported, plants performed best in the deepest medium, an effect most obvious with the forbs.

But plants grown in just 7.5 cm also survived the winter. “They’re not happy,” says Nadeau, “but they’re there.” Though she admits that insulation provided by this winter’s heavy snow-cover likely played a role, the results point to a lower limit of growth medium than one might expect – possibly making roofs more achievable in terms of initial capital costs.

Early research at the Edmonton Waste Management Centre of Excellence (again involving NAIT and Wagner students) also hints at the potential for more green roofs in the capital.

So far, Nadeau explains, compost produced by the centre is showing promising results when mixed with more expensive commercial media, offering a local solution that could possibly reduce greenhouse gas emissions caused by trucking in green roof materials, and maybe even overall costs.

Walking the walk

Just a year into the Williams Engineering green roof project, Gord Rajewski (Construction Engineering ’83) already considers it a success. “We’ve got a sustainable green roof system now,” says the company’s regional director for northern Alberta. “That was the goal.”

But for Rajewski and his staff of 50 at the Edmonton office, that success is measured as much by influence as by the health of their rooftop ecosystem. Since the roof was established, he and his team have fielded inquiries and conducted tours for organizations and businesses interested in greening up their own buildings. “There’s a real curiosity about what can be done in an urban setting,” he says.

So far, the benefits have been obvious – and measurable. The company's staff members track their own carbon footprint and greenhouse gas emissions. The thermal blanket created by the plants has decreased the strain on heating and air conditioning systems.

And for a company like Williams Engineering that emphasizes sustainability, “This is one way we can demonstrate that we can walk the walk and talk the talk,” says Rajewski.

But, he adds, “Without Leonie’s drive and involvement this probably would have never taken place. She has a lot of passion for projects of this sort. This was NAIT-driven and we were glad to be a part of it.”

New Babylon

For Nadeau, who will continue to follow up on this research even in her retirement, a green roof is “about personal satisfaction about making a difference.” It may be about even more than that.

Generations of artists and writers have been fascinated by the gardens of Babylon, featuring them as the subject of poems and paintings.

They romanticize them in a way that suggests longing for something lost. Nadeau would point to the disconnection from our natural surroundings that has come from urbanization.

Nature, says the longtime gardener, “is ingrained [in us]; it’s part of our genes.” Bringing a little green back to the concrete jungle may be an extension of that as much as a practical solution to many of the problems that environment can create. That raises a question: Do we, on some level, share the feelings of that ancient queen of Babylon, her notion of home so closely linked to its flowers and trees?

Nadeau might be inclined to think so. Pointing out our shared agrarian roots, “It was only two generations ago, really, that people began separating themselves from nature,” she says. “That’s where we come from.”