Green Roofs

Overview

A green roof is a rooftop that is partially or completely covered with a growing medium and vegetation planted over a waterproofing membrane. It may also include additional layers such as a root barrier and drainage and irrigation systems. Green roofs are separated into several categories based on the depth of their growing media. Extensive green roofs have a growing media depth of two to six inches. Intensive green roofs feature growing media depth greater than six inches (GRHC)

As green, or vegetated, roof systems become more prevalent in the United States, the benefits they can provide to a wide range of private and public entities become more apparent. These benefits are outlined below.

Additional Information

• Green Roofs for Healthy Cities

  GRHC develops and protects the market by increasing the awareness of the economic, social, and environmental benefits of green roofs, green walls, and other forms of living architecture through education, advocacy, professional development, and celebrations of excellence.

• Eco-Roof Program

  Ecoroofs replace conventional roofing with a living, breathing vegetated roof system. An ecoroof consists of a layer of vegetation over a growing medium on top of a synthetic, waterproof membrane. An ecoroof significantly decreases stormwater runoff, saves energy, reduces pollution and erosion, and helps preserve fish habitat.

Reduces Stormwater Runoff

• Green roofs can store significant amounts of water in their growing media. This water is eventually evaporated from the soil or transpired by the plants on the roof, thus reducing the runoff entering sewer systems and waterways, which can help alleviate the risk of combined sewer overflows (CSO).

Improves Air Quality

• Locally, the vegetation planted on green roofs takes up air pollutants and intercepts particulate matter.
• The cooling effect of vegetation lessens smog formation by slowing the reaction rate of nitrogen oxides and volatile organic compounds.
• By reducing energy use, green roofs lessen the air pollution caused by electricity generation.

Reduces Atmospheric CO₂

• Green roof vegetation directly sequesters carbon.
• By reducing energy use and the urban heat island effect, green roofs lower carbon dioxide emissions from regional electricity generation.

Reduces Urban Heat Island

• The local evaporative cooling provided by green roofs can reduce elevated temperatures present in urban areas as a result of heat-absorbing surfaces such as streets and conventional roofs.

Improves Community Livability

• Green roofs improve the local aesthetics of a community
• Soil and vegetation help reduce sound transmission, thus reducing local noise pollution levels.
• Green roofs can increase recreational opportunities by providing outdoor areas for people to use and enjoy. They also have the potential to foster improved community interactions that help build social capital.
• Green roofs may also provide opportunities for urban agriculture.

Improves Habitat

• Increased vegetation helps to support biodiversity and provides valuable habitat for a variety of flora and fauna.

Reduces Energy Use

• Additional insulation provided by the growing media of a green roof can reduce a building’s energy consumption by providing superior insulation compared to conventional roofing materials.
• The presence of plants and growing media reduces the amount of solar radiation reaching the roof’s surface, decreasing roof surface temperatures and heat influx during warm-weather months.
• Evaporative cooling from water retained in the growing media reduces roof surface temperatures.

Cultivates Public Education Opportunities

• Managing future economic and environmental constraints will require full community participation and partnership. Green infrastructure provides an opportunity to develop community awareness and understanding around the importance of sustainable water resource management.
• Green roofs increase community interest in green infrastructure through their aesthetic appeal, which provides a great opportunity for public education.