Green Roofs

Green roofs — also known as ‘vegetated roofs’ or ‘living roofs’ — are ballasted roofs consisting of a waterproofing membrane, growing medium (soil) and vegetation (plants) overlying a traditional roof. Well-designed, engineered and maintained green roofs provide multiple environmental, social, economic and aesthetic benefits.

GSA, which currently maintains nearly 2 million square feet of green roofs, has a long history of constructing and maintaining successful green roofs, dating back to the 1930's. Information about green roofs at GSA can be found on the agency’s Green Roof Tracker. More guidance and information about green roofs can be found at SF Tool.

Examples of GSA buildings with green roofs include:

• Social Security Administration (New Bedford, MA)
• NOAA Satellite Operations Center (Suitland, MD)
• US Coast Guard HQ (Washington, DC)

GSA green roof report

Full report: The Benefits and Challenges of Green Roofs on Public and Commercial Buildings [PDF - 9 MB]

This report, commissioned by the Office of Federal High Performance Green Buildings, includes a literature review of 200 research studies, in-depth analysis of green roof benefits, an original cost-benefit analysis, discussion of challenges and best practices, and assessment of further research needs.

Benefits of well-designed, well-maintained green roofs

The benefits section of the report includes:

• 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 roof cost benefit analysis

The report includes the cost benefit analysis for green roofs as well, and offers data including:

• GSA green roof report estimated that green roofs on commercial and public buildings provide a payback, based on 50 year average annual savings, of about 6.2 years nationally, internal rate of return of 5.2%, and an ROI of 224%, based on a net present value of $2.7/square foot.
• Primary green roof costs are related to installation and maintenance.
• Primary economic benefits of installing green roofs are lower energy costs, less frequent roof replacement due to greater durability, reduced stormwater management costs, and creation of job opportunities.

Best practices for green roof construction and maintenance

The report discusses best practices in detail on topics, including:

• Ensuring a building can structurally support a green roof
• Quality installation and leak prevention
• Maintenance requirements to avoid plant loss and other problems
• Installing green roofs on historic buildings

Future green roof research needs

The report outlines research needs, including:

• Stormwater and storm dynamics, field monitoring and computer simulation
• Long-term stormwater and energy performance
• Establishing native plants and creating habitat for endangered fauna on green roofs
• A thorough comparison between green and white (reflective) roofs
• Interaction between green roofs and solar panels
• Economics of rooftop agriculture
• Air quality improvements associated with green roofs

Visit SFTool.gov for more information on green roofs.