Green Roofs

Arlington County Courthouse Plaza Green RoofAccording to the Sustainable Facilities Tool of the U.S. General Services Administration, “Planted roofs - also known as vegetated roofs or eco-roofs - use plants as a technology to help bring the natural cooling, water-treatment and air filtration properties of vegetated landscapes to the urban environment.  These systems consist of vegetation (plants), growing medium (soil) and a waterproofing membrane, overlying a traditional roof. There are two primary types of planted roofs: extensive and intensive. Extensive planted roofs consist of small succulent plants, while intensive planted roofs have greater plant diversity, including native vegetation, bushes, or trees.”

Benefits of a Green Roof include:

  • Stormwater Management: Most urban and suburban areas contain large amounts of paved or constructed surfaces which prevent stormwater from being absorbed into the ground. The resulting excess runoff damages water quality by sweeping pollutants into water bodies. Green roofs can reduce the flow of stormwater from a roof by up to 65% and delay the flow rate by up to three hours.
  • Energy: Green roofs reduce building energy use by cooling roofs and providing shading, thermal mass and insulation.
  • Biodiversity and Habitat: Green roofs provide new urban habitat for plants and animals, like birds and insects, thereby increasing biodiversity.
  • Urban Heat Islands: Cities are generally warmer than other areas, as concrete and asphalt absorb solar radiation, leading to increased energy consumption, heat-related illness and death, and air pollution. Green roofs can help reduce this effect.
  • Roof Longevity: Green roofs are expected to last twice as long as conventional roofs
  • Aesthetics: Green roofs can add beauty and value to buildings.

Green roofs can:

  • Reduce the stormwater runoff rate from a roof by up to 65%
  • Make roof surfaces 30-40% cooler
  • Reduce heat flux from roof to building by up to 72%
  • Last 40 years or more
  • Attract such wildlife as birds, bees and spiders

Online Resources

U.S. General Services Administration: https://www.gsa.gov/governmentwide-initiatives/federal-highperformance-green-buildings/resource-library/integrative-strategies/green-roofs

U.S. EPA: Using Green Roofs to Reduce Heat Island: https://www.epa.gov/heatislands/using-green-roofs-reduce-heat-islands

Whole Building Design Guide: https://www.wbdg.org/resources/extensive-vegetative-roofs

Article: Study Finds Green Roofs Make Solar Panels More Efficient: https://www.greenroofs.com/2021/08/28/study-finds-green-roofs-make-solar-panels-more-efficient/ Study from the City of Sidney, Australia.