Green Roof / Blue Roof

What is it?

Rutgers University Business School Green Roof

A green roof is a system of lightweight soil mix and plants. The plants absorb some of the rain that falls on the roof, and any excess is stored in a soil layer below. Layers of soil and plants are as thin as just a few inches, or as thick as several feet depending on the structural capacity of the building and the types of plants that are used. Roofs with a thin soil layer are lighter and easier to install, and are usually planted with succulent plants that need minimal water and nutrients to survive. Thick green roofs can support a greater variety of plants, including grasses and flowering perennials, but tend to be more expensive.

Blue roofs are non-vegetated systems that hold stormwater. They can be designed as modular trays with loose stones, specialized permeable pavers, or just a waterproof membrane. The infrastructure for this system is less costly than a green roof, but does not have any aesthetic value.

Blue Roof. Image Credit: NYC Department of Environmental Protection

Benefits include:

  • Better temperature regulation on the roof surface
  • Lower heating and cooling costs
  • Recreational and public space areas for a project with a tight
    footprint

When is it used?
Green roofs may sometimes be installed on slightly sloped roof surfaces, while blue roofs are only suitable for flat roofs. Both systems can be built during new construction or modified onto an existing roof.

What are some key general considerations?

  • Rooftops must be evaluated for structural considerations before a green or blue roof can be installed.

*Blue roofs are not currently recognized as GI by NJDEP.

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