A green roof is a roof of a building, partially or completely covered, with vegetation, soil (or a growing medium), planted over a waterproofing membrane. The term is used to indicate roofs that utilize “green” technology, such as solar panels or a photovoltaic module. Green roofs are also referred to as eco-roofs, vegetated roofs and living roofs. Rooftop ponds are another form of a green roof, and are used to treat gray water.

History of Green Roofs

Today’s green roofs are made of a system of manufactured layers deliberately placed over roofs to support growing medium and vegetation. Originally developed in Germany in the 1960s, green roofs are becoming increasingly popular in the United States.

Benefits of Green Roofs

  • Dramatically improve a roof’s insulation value
  • Lengthen a roof’s life span by up to three times
  • Reduces heating and cooling, by 26 percent
  • Filter pollutants and CO2 out of the air, and heavy metals out of rainwater
  • Provide amenity space for building users — replaces a yard or patio
  • Grow fruits, vegetables and flowers
  • Complements wild areas by providing “stepping stones” for songbirds, migratory birds and other wildlife facing shortages of natural habitat.

Uses of Green Roofs

  • Green roofs are installed to comply with local government regulations, often regarding storm water runoff management. Green roofs slow the rate of runoff from the roof, and decrease the total amount of runoff.
  • Green roofs help to reduce the heat effects of traditional materials that customarily increase a city’s heat by 7 degrees (as compared to surrounding areas).
  • Used for rooftop water purification.

Categories of Green Roofs

Green Roofs are known as “intensive”, “semi-intensive,” or “extensive”, depending on the depth of planting medium and the amount of maintenance needed.

  • Traditional roof gardens need a reasonable depth of soil to grow large plants or conventional lawns, and are considered “intensive,” — since they are labor-intensive, requiring irrigation, feeding and other maintenance.
  • “Extensive” green roofs are designed to be virtually self-sustaining and require a minimum of maintenance. There are pitched green roofs or flat green roofs. Pitched roofs tend to be of a simpler design than flat green roofs. Pitched roofs reduce the risk of water penetrating through the roof structure, allowing the use of fewer waterproofing and drainage layers.

Examples of Green Roofs

  • The new California Academy of Sciences in San Francisco will provide 2.5 acres of native vegetation designed as a habitat for indigenous species, and will consume 30-35 percent less energy than required by code.

Disadvantages of Green Roofs

  • More demanding structural standards.
  • Certain buildings cannot be retrofitted with a green roof due to weight load of soil and vegetation.
  • Depending on roof type, maintenance costs could be higher.