Landscape Architects Release Green Roof Performance Report

Roof Retained 27,500 Gallons of Stormwater in First Year

Sep 19, 2007, 01:00 ET from American Society of Landscape Architects

    WASHINGTON, Sept. 19 /PRNewswire-USNewswire/ -- The American Society of
 Landscape Architects' (ASLA) green roof retained thousands of gallons of
 stormwater, reduced building energy costs by hundreds of dollars a month,
 and significantly lowered outdoor air temperature according to a report
 today from the association. The report examined various components of
 ASLA's green roof demonstration project, ranging from water and temperature
 monitoring to individual plant performance.
     "Because landscape architects are leading in the design of green roofs
 across the country, it was important for us to build a demonstration
 project and measure the impact green roofs have on their surrounding
 communities," said Nancy Somerville, Executive Vice President and CEO of
 ASLA. "The findings show that our green roof delivered significant economic
 and environmental benefits."
     In 2006, ASLA replaced the conventional roof on its downtown
 Washington, DC headquarters with a green roof, installing equipment to
 gather data on stormwater runoff, water quality, and temperature.
     From July 2006 to May 2007, ASLA's green roof prevented 27,500 gallons
 of stormwater -- nearly 75 percent of all precipitation on the roof -- from
 flowing into Washington, DC's overburdened sewer and stormwater system.
 Except during repeated heavy rains, the roof only created runoff during
 rainfalls that exceeded one inch. The water runoff itself contained fewer
 pollutants than typical water runoff.
     ASLA's green roof lowered air temperature by as much as 32 degrees in
 the summer when compared to a neighboring tarred roof, helping mitigate the
 urban heat island effect.
     "Collectively, green roofs can save billions of dollars in urban
 infrastructure costs, which is why more and more cities are encouraging
 them through tax and other incentives," Somerville continued.
     The roof also reduced the building's energy costs-especially in the
 winter. Engineering analysis showed that the green roof's extra insulation
 lowered energy usage in the winter by 10 percent with a potential of two to
 three percent in the summer.
     When designing the green roof, ASLA experimented with varying types of
 plants. The extreme nature of the rooftop environment allowed some to
 thrive while others struggled. On the extensive portion of the roof, hardy
 species of Sedum (Sedum album, Sedum reflexum, Sedum spurium, and Sedum
 sexangulare) performed well over other Sedum species (Sedum lanceolatum and
 Sedum stenopetalatum). Delosperma nubigenum (Ice Plant) did well in many
 areas but not well in the north terrace.
     On the intensive portion, Rhus copallina (Flame Sumac), Rhus aromatica
 (Smooth Sumac), Campsis radicans (Ttrumpet Vine), and Rosa Carolina
 (Pasture Rose) were successful while Ceonanthus americanus (New Jersey Tea)
 struggled. Detailed information can be found at
     The full briefing report and the comprehensive water monitoring report
 can be found at
     About ASLA
     Founded in 1899, ASLA is the national professional association for
 landscape architects, representing more than 17,600 members in 48
 professional chapters and 68 student chapters. Landscape architecture is a
 comprehensive discipline of land analysis, planning, design, management,
 preservation, and rehabilitation. ASLA promotes the landscape architecture
 profession and advances the practice through advocacy, education,
 communication, and fellowship. Members of the Society use their "ASLA"
 suffix after their names to denote membership and their commitment to the
 highest ethical standards of the profession.
     Learn more about landscape architecture online at

SOURCE American Society of Landscape Architects