Green Roofs and Urban Agriculture
Sustainable Design Contributes to Water Conservation and Habitat
Oct 2, 2008
From rooftop gardens to big box stores in North America, green roofs are a hot item in sustainable design. They promise better views for neighbouring buildings, diminish the heat island effect, and contribute to water conservation measures.
Green roofs have been in use since the Middle Ages in Europe, and sod roofs were a feature of pioneer homes in North America. After the oil crisis of the early 1970’s, Germany experimented with roof landscaping for energy conservation purposes. That country boasts more than 13 million square metres of green roofs.
With green roofs proliferating in sustainable design circles, standards for their design and construction have been established and field tested. The British Columbia Institute of Technology (BCIT) has developed a Centre for the Advancement of Green Roof Technology with a focus on developing green roof and living wall technologies for the BC coastal region. Lessons learned here are being applied in other jurisdictions.
What is a Green Roof?
BCIT defines green roofs as engineered roofing systems incorporating the use of vegetation that make environmental, economic and social contributions to urban areas. It distinguishes between three kinds of green roof:
- Extensive green roofs, ideal for large flat-roof buildings and apartments and requiring little maintenance after being established
- Intensive green roofs, or rooftop gardens requiring regular maintenance much like an at-grade garden
- Semi-intensive green roofs which combine aspects of both of the above roofs
Green Roof Benefits
The benefits of green roof design are numerous. Millennium Water is a new community in Southeast False Creek that will serve on a temporary basis as the City of Vancouver’s Olympic Village for the games in 2010. Green roofs will ultimately cover 50 percent of the whole site, with design by Durante Kreuk Landscape Architects.
Roofs will be planted with a growing medium suitable to the local climate. This vegetation will retain rainwater, returning a portion to the atmosphere through evaporation and transpiration. This evaportranspiration as it is called reduces the urban heat island effect, cooling rather than heating a building in summer. Planted roof surfaces minimize heat loss in winter.
Stormwater from a green roof is cleaner than runoff from a conventional roof, and will be stored in cisterns or harvested for plumbing at False Creek. Reusing stormwater will result in less stress on stormwater infrastructure and sewers; this in turn translates into cost savings for the site’s developers.
Other benefits of green roofs include improved air quality, longevity of roofing materials, urban habitat for wildlife, and competitive lifecycle costs. Buildings with green roofs qualify for credits under the US and Canadian Green Building Council LEED certification system.
Planning for Green Roofs
Green roof design requires planning not only for the live and dead load of the roof and its growing medium, but provisions must also be made for managing stormwater runoff and maintenance of the roof growing medium. Structural engineers determine the load bearing capacity required for different kinds of green roofs.
Another consideration is building insurance. Insurers for buildings with extensive green roof systems prefer to be included early in the design process, assuring that the type of green roof system and growing media will not contribute to fanning fires or other problems.
Net zero architecture aims to diminish a building’s carbon footprint and impact on the environment. The incorporation of green roofs facilitates achieving both these objectives while helping developers and builders collect LEED credits.
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