Green roof technology helps lower the cooling costs of a building by significantly decreasing the temperature of the roof and the air around A/C unit intake vents. A green roof at the Ford truck plant in Dearborn, Mich., reduced the building's annual energy consumption by 7% (Earth Pledge, 2005).
Aesthetics & Marketability
Green roofs transform underutilized, barren landscapes into verdant, urban oases. GIS studies have shown that real estate within 800 feet of green space increases in value by up to 22% (Nicholls, 2004). Green roofs demonstrate a visual commitment to local and regional sustainability.
Increased Roof Membrane Life
Waterproof membranes without the protection of a green roof need to be replaced every 10 to 20 years. With a green roof, building owners may need to replace a membrane only once during their building ownership; there are waterproof green roofs in Europe that are over 100 years old (Earth Pledge, 2005).
A 1988 study demonstrated that the availability of a natural view can be instrumental in the alleviation of daily stress and physical ailments, a decrease in the number of sick days taken, and an increase in worker satisfaction and productivity (Kaplan, 2001).
Local Food Production
A food roof can grow up to three pounds per square foot of vegetables in a season. The Fairmont Waterfront Hotel in Vancouver, B.C., produces $25,000 to $30,000 worth of herbs and produce annually (Kingsbury, 2008).
A green roof has a burning heat load of 3 kWh/m² while a three-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.
According to the U.S. 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.
Improved Medical Recovery Time
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 than hospitals without green spaces (Peck, 2008).
Green roofs can help reduce external noise pollution by 10 to 50 decibels, depending on the thickness of the system (Cities, 2006).
At Novartis Lab in Cambridge, an extensive green roof and paver patio overlooking the park create a rooftop respite for staff.
Green roofs reduce and delay stormwater runoff, helping to prevent combined sewer overflow (CSO) events. CSOs occur when stormwater discharge from heavy precipitation floods sewer systems and sends a combination of stormwater and raw sewage into the watershed. Extensive green roofs in particular can retain an average of 75% annual rainfall and delay runoff by 3 to 4 hours (Weiler, 2009). Green roofs also filter pollutants from rainwater, roofing materials, and atmospheric deposition.
Improved Air Quality
Green roofs and walls absorb airborne particles and carbon dioxide while releasing oxygen, effectively filtering and cleaning our atmosphere. They also reduce the ambient summer temperature around a building, allowing it to draw less energy for air conditioning and to lower CO2 emissions (Coutts et al., 2015).
Urban Heat Island Reduction
Impervious surfaces in urban centers absorb and retain solar radiation, leading to higher average air temperatures in cities compared to suburban and rural areas. Urban heat island effect has negative repercussions on human health, surrounding watersheds, and energy consumption. Green roofs reduce urban heat island effect by dramatically lowering rooftop temperatures through shading and evapotranspiration, keeping surrounding air temperatures cool. (Coutts et al., 2015).
Redevelop Migratory Corridors and Ecosystems
Green roofs replace ecosystems that have been displaced by city infrastructure. High-rise build spaces can create habitat for essential pollinators, migratory birds, native plant species, and more. The non-profit organization CICEANA in Mexico City uses a roof to cultivate and protect 25 different species of endangered native plants (Earth Pledge, 2005).
The average food product in the U.S. 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.
Fenway Farms is a 7,000-square-foot rooftop farm designed to provide over 4,000 pounds of organic produce for the ballpark each year.
Cities, G. R. (2006). Green Roof Design 101.
Coutts, E., Ito, K., Nardi, C., Vuong, T., (2015). Planning Urban Heat Island Mitigation in Boston. Trust for Public Land. Retrieved January 2016 here.
CUESA: Center for Urban Education about Sustainable Agriculture. Why Farmers Markets'. Retrieved Fall 2016 here.
Earth Pledge. (2005). Green Roofs: Ecological Design and Construction. Atglen: Shiffer Publishing.
environmentalleader.com. (2007, November 21). Retrieved December 2009, from environmentalleader.com.
Green Roofs for Healthy Cities. (2005). agreenroof.org. Retrieved December 2009, from agreenroof.org.
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.
Nolan, C. M. (2009, Fall). Leading by Example. Living Architecture Monitor,
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,
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.