Greening the City

Investigating the Benefits of Green Roofs and Roof Gardens

The return of the roof garden heralds a new era of greening our urban spaces. Studies espousing the virtues of greenery and fresh air have encouraged many to find environmentally friendly uses for dead roof space. Green roofs and roof gardens offer environmental benefits and save costs for building owners.

In addition to their aesthetic appeal, green roofs and roof gardens reduce the heat absorption of the building. If a significant number of roofs are greened, they can reduce the heat island effects of cities. For example, the temperature of Tokyo can be reduced by 0.11 to 0.84 degrees Celsius if half of the rooftops were green. This would result in a savings of $1.2 million a day in energy used to cool buildings in the city. Green roofs capture rain water and reduce run off so storm water drains are better able to cope in times of high rainfall. They improve the air quality and filter smog and pollution from cars and factories. Plants absorb sound and reduce noise pollution. They offer aesthetic appeal and enhance biodiversity.

Roof gardens provide space to grow fruits and vegetables. Planting in containers and utilizing hydroponics can reduce a rooftop garden’s weight and negate the need for additional waterproofing. Lufa Farms in Montreal is an excellent example of the creative use of dead roof space. Lufa farms rent a 31 000 square foot space on the top of an office block in the city of Montreal. They utilize tunnels and hydroponics to grow tomatoes, cucumbers, peppers and other crops year round. The setup costs were higher than those associated with conventional farming methods, but the running costs are much lower. Lufa has the added advantage of being able to do business straight from the greenhouse to the customer. Lufa Farms delivers baskets of veggies to customers on a weekly basis. The reduction of spoilage, transport and the middleman, reduces costs for the customer and increases profits for the farm. The farm was turning a profit from its second year and has saved 25 percent in heating and cooling costs for their host building.

Courtesey of Magellan and Eric Hausman

Intensive roofs, or rooftop gardens, create aesthetically pleasing spaces and for entertainment. They can support the growth of lawns, trees and shrubs. They are mini parks on roof tops with an excellent view. Extensive or green roofs are designed to reduce solar absorption and improve insulation. The entire roof area is covered with roof panels that are only up to a foot thick to reduce weight. Shallow root plants capable of withstanding inclement weather are utilized to cover the roof and block as much as 87 percent of solar radiation.

A recent study conducted by the Montreal Urban Ecology Center to investigate the effectiveness of green roofs yielded some surprising results. After greening the roof of a 100-year-old duplex at Plateau Mont Royal, air conditioning use dropped by 91 percent while heating was reduced by 27 percent.

The city of Toronto offers incentives to encourage green roofing in the city. To find out if you qualify, follow this link Eco-Roof Incentive Program

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