Green Roofs

What is a Green Roof?

  • A green roof is a roof that has been covered with living vegetation that will provide stormwater management and other benefits.
  • A green roof can be added to an existing roof, and can cover all or part of the roof.
  • A green roof is typically a “passive” space—where plants are growing but human access is limited to installation and maintenance. A vegetated roof that is intended as a space for people to utilize is called a “roof garden.” Both have stormwater benefits, but green roofs typically provide greater stormwater retention.

    • Why Develop a Green Roof?

  • Green roofs provide a lush oasis in the city, helping to reduce the “urban heat island” effect, produce fresh oxygen, serve as a natural habitat and reduce heating and cooling costs for a building by acting as an additional layer of roof insulation.
  • Green roofs retain stormwater and reduce the flow of stormwater during a rain event.
  • Green roofs help to filter pollutants from the excess stormwater that runs off of the roof.

    • Facts About Green Roofs

  • Green roofs have been proven to absorb and permanently retain up to 50% of the rainfall they receive.
  • Green roofs range in cost from $10 per square foot for an extensive green roof to $25 per square foot for an intensive green roof, and will extend the lifetime of the roof by 100-200%.
  • An extensive green roof contains up to six inches of soil, is lightweight, accommodates shallow-rooted plant species and provides baseline stormwater, insulation and ecological benefits.
  • An intensive green roof contains more than six inches of soil, accommodates a variety of plants including grasses, ground covers, ornamentals and vegetable plants, requires a greater roof load and provides maximum stormwater, insulation and ecological benefits.
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    Thinking of Developing a Green Roof?

  • The most cost-effective time to construct a green roof is when the building is being constructed or when the roof needs to be replaced.
  • Determine whether you want to design and install the roof yourself, or hire a contractor to manage the project.
  • Determine the capacity of your building to sustain a green roof by hiring a licensed professional, such as a structural engineer or architect, to examine the existing roof structure.
  • Take into consideration the height of the roof (which increases wind speed), roof pitch, budget, roof accessibility and maintenance capabilities.
  • Develop a green roof design (in partnership with professionals) that contains a root barrier, membrane protection, drainage system, moisture mat, growing media and plant species.
  • For a low-maintenance, drought-resistant green roof, plant Sedum species (succulents), which are ideal for green roofs. Certain native grasses and other species are also appropriate.
  • Acquire the appropriate permits needed through the Department of Licenses and Inspection.
  • Philadelphia businesses can apply for a Green Roof Tax Credit that will provide a rebate for 25% of green roof costs up to $100,000. See below for more information.
  • If a green roof is cost-prohibitive, a rooftop garden is a simple and low-maintenance alternative. Potted plants placed on the roof will also help to absorb stormwater. However, rooftop plants should ideally be drought-resistant and require minimal watering. Roof load and accessibility must be considered when developing a rooftop garden, as potted plants full of water will add substantial weight to the roof.

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    Green Roof Gallery

    The type of green roof you develop will depend on the type of building, the structural capacity of the roof, whether or not the roof will be used as a recreational space or active garden, and what level of stormwater absorption and insulation effects are desired. Check out the gallery below to view a variety of green roof types.


    Passive Commercial Green Roof


    Intensive Green Roof Utilized for Vegetables and Flowers


    Installation of a Residential Green Roof


    Rowhome Roof Garden


    Passive Green Roof on Rowhome


    Instructional Guides:
    Portland Ecoroof Guide
    Living Roofs
    Green Roof Manual
    Green Roof FAQ

    Philadelphia Green Roof Business Tax Credit:
    Green Roof Business Tax Credit Summary
    Green Roof Business Tax Credit Instructions
    Green Roof Business Tax Credit Application

    For more information on the tax credit application process, contact the Philadelphia Industrial Development Corporation: 215-496-8020 info@pidc-pa.org

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