As land continues to be replaced with concrete surfaces due to population growth and urbanization, the necessity to recover green space is becoming increasingly critical to maintain environmental quality. Installing green roofs is one option that can reduce the negative impact of development while providing numerous environmental, economic, and social benefits. They can improve stormwater management by reducing runoff and improving water quality, conserve energy, alleviate the “urban heat island”, increase longevity of roofing membranes, reduce noise and air pollution, cut carbon, increase urban biodiversity by providing habitat for wildlife, provide space for urban agriculture, provide a more aesthetically pleasing and healthy environment to work and live, and improve return on investment compared to traditional roofs.
How do Green roofs reduce stormwater runoff?
During heavy or continuous rain, runoff can overwhelm stormwater infrastructure and potentially damage waterways and fish habitat.
• Green roof growing media retain rainwater and, together with plants, return a portion of this water to the atmosphere through evaporation and transpiration (evapotranspiration).
• Stormwater that does leave the roof is delayed and reduced in volume.
• Stormwater that runs off a green roof is cleaner than runoff from a conventional roof.
• Retention and delay of runoff eases stress on stormwater infrastructure and sewers.
• Cost savings from decentralized stormwater mitigation reduces the need to expand or renovate related infrastructure.
How are green roofs energy efficient?
Green roofs reduce the heat flux through the roof, and less energy for cooling or heating can lead to significant cost savings. Shading the outer surface of the building envelope has been shown to be more effective than internal insulation.
• In summer, the green roof protects the building from direct solar heat.
• In winter, the green roof minimizes heat loss through added insulation on the roof.
• Energy conservation translates into fewer greenhouse gas emissions.
How do green roofs improve air quality?
Plant leaves trap dust particles from the air, and evapotranspiration cools ambient temperatures.
• Less ground level ozone + less heat = less smog.
• Reduced Urban Heat Island profile.
• Less need for health care services result in societal cost savings.
How can green roofs serve as habitats?
As undisturbed areas, rooftops can serve as refuge for creatures that struggle for survival. Ground-nesting birds, such as Killdeer, use green roofs for nesting and raising their young.
• Vegetated rooftop habitats can serve as stepping stones, to create corridors connecting other patches (roofscape or at grade) across an urban sea to natural habitats beyond the city.
• Natural habitats can serve as templates for green roofs designed for biodiversity.
• Low maintenance green roofs can be designed to serve as refuge for species such as ground-nesting birds.
A goose nest on a roof on Granville Island, Vancouver.
How do green roofs last longer than traditional roofs?
Green roofs cover the waterproofing membrane, protecting it from UV rays and extreme daily temperature fluctuations. This protection extends the lifespan of the waterproofing twice as long as conventional roofing, meaning that membranes under green roofs last twice as long as those on traditional roofs.
• Reduced material waste from re-roofing.
• Less frequent re-roofing, less costs over time.
Washington DC City Centre Project / Photo Source: @urbanstrongnyc
How do green roofs provide ‘extra’ space?
Green roofs make the most of unused space within the increasing density of our cities. Rooftops can be developed into social and recreational spaces and used for urban agriculture.
• Amenity space for day care, meetings, and recreation.
• Improved aesthetic views for neighbours in adjacent buildings.
• Improved worker productivity and creativity.
• Potential to enhance urban food security through rooftop gardening and food production.
Photo Source: Instagram @neidaarrington