Kinds of Green Roofs and Benefits

Intensive green roofs

Intensive green roofs involve roof gardens with soil, or other growing medium, that is more than six inches deep. These provide open space for people and gardens that can produce herbs and vegetables. These roofs often require maintenance and irrigation systems. For intensive green roofs a large variety of plants are possible due to the thick planting medium layer which allows for deeper rooted plants such as: bushes, grasses, and even trees, to grow.

Extensive green roofs

Extensive green roofs have soil, or other growing medium, less than four to six inches deep and provide aesthetic and ecological benefits to the building and surrounding area. These roofs are often self-sustaining and require minimal maintenance. For extensive green roofs best plants are generally those that are low-growing, shallow rooted perennials that tolerate heat, cold, sun, wind, drought, salt, insects, and disease. Hardy succulents, which offer good ground cover, are often the primary plants and work horses on an extensive green roof.

Green Roof Benefits

Understanding the popularity and interest in green roofs might best be done by considering the benefits of green roofs and how they can accomplish multiple goals. Green roof benefits can include:

• Reducing storm water runoff (by as much as 75%), as well as providing filtration that improves water quality
• Providing a habitat for animals and insects that is otherwise eliminated by development
• Reducing energy costs, providing insulation, and reducing roof replacement costs

The aesthetic benefits of roofs have long been a design concern in architecture. In the late nineteen-hundreds, William Morris wrote on the topic of the external appearance of roofs, saying: "And where... new buildings must be built, by building them well, and in a common-sense and unpretentious way, with the good material of the countryside, they will take their place alongside of the old houses and look, like them, a real growth of the soil."

Peggy Notebaert Nature Museum extensive green roof

(photo credit: © Conservation Design Forum)
Peck, Steven W. Award Winning Green Roof Designs: Green Roofs for Healthy Cities (Atglen, PA: Schiffer). p. 76-77. Crerar SB419.5.P43 2008

Millennium Park intensive green roof

Peck, Steven W. Award Winning Green Roof Designs: Green Roofs for Healthy Cities (Atglen, PA: Schiffer).  p.139. Crerar SB419.5.P43 2008

Searle Chemistry Laboratory’s extensive green roof

5735 S. Ellis Avenue. Photo by Cheryl Rusnak.