Comparative Life Cycle Assessment of Standard and Green Roofs

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Environ. Sci. Technol. 2006, 40, 4312-4316 Comparative Life Cycle Assessment of Standard and Green Roofs SUSANA SAIZ,† C H R I S T O P H E R K E N N E D Y , * ,† BRAD BASS,‡ AND KIM PRESSNAIL† Department of Civil Engineering, University of Toronto, 35 St. George Street, Toronto, Ontario, Canada M5S 1A4, and Adaptation & Impacts Research Group, Environment Canada at University of Toronto Life cycle assessment (LCA) is used to evaluate the benefits, primarily from reduced energy consumption, resulting from the addition of a green roof to an eight story residential building in Madrid. Building energy use is simulated and a bottom-up LCA is conducted assuming a 50 year building life. The key property of a green roof is its low solar absorptance, which causes lower surface temperature, thereby reducing the heat flux through the roof. Savings in annual energy use are just over 1%, but summer cooling load is reduced by over 6% and reductions in peak hour cooling load in the upper floors reach 25%. By replacing the common flat roof with a green roof, environmental impacts are reduced by between 1.0 and 5.3%. Similar reductions might be achieved by using a white roof with additional insulation for winter, but more substantial reductions are achieved if common use of green roofs leads to reductions in the urban heat island. Introduction Green roofs are among several technologies for developing more environmentally sustainable buildings and creating visually attractive urban environments. Recent high profile green roof projects in North America, for example, include those for Chicago City Hall, Henry Ford’s Rouge automobile plant, and the new War Museum in Ottawa. Green roofs have been more common in central Europe and are now being constructed on buildings around the world. There are several potential benefits provided by the inclusion of greenery in cities through

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