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Green roof technology helps lower the cooling costs of a building by decreasing the temperature of the roof and the air-intake around A/C units.
A 2003 study by the National Research Council of Canada found that green roofs can reduce summer energy demand by up to 75% in a single story building.
The green roof on the Ford Truck Plant in Dearborn, Michigan reduced the building's annual energy consumption by 7%. (Earth Pledge, 2005)
Chicago City Hall installed a 22,000 ft2 semi-intensive green roof and updated their HVAC system to reduce their monthly energy bill by $10,000. (Nolan, 2009)
The GAP, Inc. Headquarters in San Bruno, CA installed a 69,000 ft2 extensive green roof and reduced their annual energy consumption by an estimated $25,000, an 11 year ROI. (Cities, 2006)
Green roofs increase the longevity of a waterproof membrane by at least 2 to 3 times its average lifespan by protecting the waterproof membrane from:
- UV rays, electromagnetic radiation and falling objects (Cities, 2006)
- Extreme temperature fluctuations in the summer: A black roof will fluctuate between 150ºF and 70ºF in 12 hours, while a green roof maintains a consistent temperature around 80ºF (Kingsbury, 2008).
- Freeze/thaw cycles during the winter
Waterproof membranes without the protection of a green roof need to be replaced every 10 to 20 years while some green roofs in Europe are over 100 years old and still waterproof (Earth Pledge, 2005). This effectively helps reduce landfills by reducing the amount of membranes being thrown away.
Green roofs transform an underutilized, barren landscape into an urban oasis.
Residential and commercial building owners can charge higher rental rates if green space is either accessible or simply in view.
GIS studies have shown that real estate within 800 feet of green space increases in value by up to 22%. (Nicholls, 2004)
The Fairmont Waterfront Hotel in Vancouver, BC produces $25,000 to $30,000 worth of herbs and produce annually (Kingsbury, 2008).
A food roof can grow up to 3 pounds per square foot of vegetables in a season. See an example of a food roof in use here.
Green roofs can help reduce external noise pollution by 10 to 50 decibels depending on the thickness of the system (Cities, 2006).
The green roof at Gap headquarters near the San Francisco International Airport reduced noise pollution by 50 decibels (Kingsbury, 2008).
In the 1880s, German roofer H. Koch put a layer of soil and gravel on tar roofs to prevent roof fires. These roofs were germinated by wild seeds, and the modern green roof was inspired 70 years later when these roofs were found to be still intact and waterproof, having survived 2 world wars (Earth Pledge, 2005).
A green roof has a burning heat load of 3 kWh/m² while a 3-ply bitumen roofing system, a common membrane type, has a burning heat load of 50 kWh/m². (M Koehler, 2003) This means that the heat from a fire on a green roof will be 1/16th the heat from a bitumen system.
Some plants are more fire resistant then others. Succulents such as sedums contain water and are difficult to burn. Grass, however, can dry out during drought conditions and become more flammable.
Studies have shown that patients recover more quickly when they have access to green spaces.
Hospitals with open green spaces record patient check-out times 2.5 days earlier then hospitals without green spaces (Peck, 2008).
The 10,000 sq ft green roof on the Schwab Rehabilitation Hospital in Chicago also serves as a rooftop park and garden for horticultural therapy, a process in which plants and gardening activities are employed to improve body, spirit and mind (Green Roofs for Healthy Cities, 2005).
A 1988 study demonstrated that the availability of a natural view can be instrumental in the alleviation of daily stress, physical ailments, a decrease in the number of sick days taken, and an increase in worker satisfaction and productivity (Kaplan, 2001).
Worker productivity in green office buildings increases by 2-16% (Peck, 2008).
Green roofs demonstrate a visual commitment to local and regional sustainability.
According to the US Green Building Council, green roofs can receive up to 23 LEED credits for various categories including sustainable sites, water efficiency, energy and atmosphere, and innovation and design process.
Green roofs reduce and delay stormwater runoff, helping to mitigate combine sewage overflows (CSOs), which result when storm water floods a city's sewer system and discharges raw sewage into the local watershed. Green roofs also filter pollutants from rainwater, roofing materials, and atmospheric deposition.
• Extensive green roofs can retain an average of 75% annual rainfall and delay runoff by 3 to 4 hours (Susan K. Weiler, 2009).
• A study conducted by Environment Canada found that if Toronto covered 6% of available roof space with green roofs, it could retain 127 million cubic feet of rain water per year. The storage tank needed to hold the same amount of rainwater would cost $60 million while the green roofs needed would cost $45 million.
• The 10.4 acre green roof on the Ford Dearborn Truck Plant retains approximately 4 million gallons of rainwater each year (XeroFlor).
• The 18,000 square foot green roof atop Radio City Music Hall will prevent approximately 566,000 gallons of water from entering New York City's sewage system (environmentalleader.com).
The average food product in the US travels 1,500 miles before reaching a consumer, increasing food costs and CO2 emissions (CUESA). Food roofs in urban communities bring high-quality fruits, vegetables, and herbs to densely populated areas. They promote healthy eating, create jobs, and allow for a more sustainable, seasonal food system. Please refer to our Portfolio page to view our Food Roof projects.
Air temperatures in urban areas have increased by 2ºF per decade over the last 50 years and are now 7 to 11ºF higher than in the surrounding undeveloped areas. Green roofs can alleviate the Urban Heat Island effect by covering black rooftops, one of the hottest factors in the urban environment, with cool, green surfaces.
Black roofs can reach temperatures of 150ºF while green roofs rarely exceed 86ºF (Kingsbury, 2008).
Green roofs absorb airborne particles and carbon dioxide while releasing oxygen, effectively filtering and cleaning our atmosphere. By reducing the ambient summer temperature around a building, less energy is needed for air conditioning, and thus produce fewer CO2 emissions.
• The green roof on the Ford Truck Plant in Dearborn Michigan is predicted to improve the air quality around the building by 40% by absorbing dust and breaking down hydrocarbons (Earth Pledge, 2005).
Green roofs keep waste out of landfills by using recycled materials and by extending the life of a roof by two to three times its average life span.
Green roofs replace ecosystems that have been displaced by city infrastructure. High-rise build spaces create habitats for various species and insects, particularly birds traveling north and south.
• The 2.5 acre green roof on the California Academy of Science consists of native vegetation designed as a habitat for indigenous species, including the threatened Bay Checkerspot butterfly (California Academy of Science).
• Mexico City’s nonprofit organization CICEANA cultivates 25 endangered native plants on its roof (Earth Pledge, 2005).
Cities, G. R. (2006). Green Roof Design 101.
Earth Pledge. (2005). Green Roofs: Ecological Design and Construction. Atglen: Shiffer Publishing.
environmentalleader.com. (2007, November 21). Retrieved December 2009, from www.environmentalleader.com.
Green Roofs for Healthy Cities. (2005). www.agreenroof.org. Retrieved December 2009, from www.agreenroof.org: http://www.greenroofs.org/washington/index.php?page=schwab
Kaplan, R. (2001, July). The nature of the view from home. Environment and Behavior , pp. 507-542.
Kingsbury, N. D. (2008). Planting Green Roofs and Living Walls. London: Timber Press.
M Koehler, M. S. (2003). Photovoltaik-Panels on Greened Roofs. World Climate & Energy Event (pp. 151-158). Rio: Krauter.
Nicholls, S. (2004, March). Measuring the impact of parks on property values: new research shows that green spaces increase the value of nearby housing. Parks & Recreation .
Nolan, C. M. (2009, Fall). Leading by Example. Living Architecture Monitor , p. 14.
Osmundson, T. (1999). Roof Gardens: History, Design, and Construction. New York: W.W. Norton & Company.
Peck, S. (2008, Fall). A robust and green economy. Living Architecture Monitor , p. 4.
Susan K. Weiler, K. S.-B. (2009). Green Roof Systems. Hoboken: John Wiley & Sons.
Wilson, A. (2005, April). Making the Case for Green Building. Environmental Building News .