Green roofs are building roofs that are partially or completely covered with plants and soil planted on top of a waterproof layer. They may also include root barriers and drainage and irrigation systems. The purpose of green roofs is to reduce the volume and pollutant load of stormwater runoff.
Distinguished by the depth of their root zone, there are two primary types of green roofs: 1) Extensive green roofs, which provide 4 to 6 inches of root zone and are low maintenance, but they are typically not accessibly to the public and 2) Intensive green roofs, which provide over 6 inches of root zone and provide park-like amenities with public access, but are more expensive and require regular maintenance.
- A reduction in runoff volume from rooftops through evaporation and absorption.
- A reduced pollutant load due to filtration provided by soil and root beds.
- An increased in the aesthetic value and the availability of park-like, recreational amenities.
- According to the U.S. EPA, green roofs provide the following:
- Reduced urban heat island effects.
- Increased thermal insulation and energy efficiency, resulting in lower heating and cooling costs.
- Increased acoustic insulation.
- Increased durability and lifespan when compared to conventional roofs.
- Must be functional, maintainable and attractive to ensure long-term success.
- May be installed as part of new construction or retrofitted onto existing structures.
- Suitable for commercial, industrial and residential applications.
- Sustainability is enhanced with the use of a cistern system that can provide irrigation needs.
- May require additional structural reinforcement for support purposes.
- Choosing the proper landscaping is critical to the performance of a green roof.
- Select native vegetation with root structures that are compatible to the available depth.
- Selected plant species that can withstand direct sunlight and dry conditions.
- Consider maintenance requirements and low maintenance groundcover-type vegetation.
Green roofs like this one utilize plants that are native to the area so that they need minimal maintenance. Courtesy of Roofscapes, Inc.
Water that runs off of a green roof has higher water quality than that which falls from a traditional roof. Courtesy of UCF Stormwater Management Academy
The surface temperature of a vegetated roof is often cooler than the air temperature, reducing the urban heat island effect. Courtesy of Eric Livingston