Image Credit: Andropogon, 2020
Photograph Image Credit: Andropogon, 2020

Green Roof


A green roof is a system of lightweight soil 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 roof and the types of plants that are specified. Roofs with a thin soil layer are lighter and easier to install, and are usually planted with succulents that need minimal water and nutrients to survive. Green roofs with thicker soil profiles can support a greater variety of plants, including trees and shrubs, but are more expensive.

Benefits include:

  • Better temperature regulation on the roof surface
  • Minimizes land used for stormwater management, allowing for more recreational and public space area

Deconstructed Green Roof
Image Credit: Mekobre, 2018

Paseo Verde Green Roof
Image Credit: Zelen Architecture, 2018

Considerations:

  • The structural capacity of an existing or proposed roof should be considered before proposing a green roof.
  • Green roofs can be combined with blue roof systems to maximize the effectiveness of stormwater storage while maintaining the aesthetic and recreational value that green roofs provide.
  • Green roof plant palettes should consider seasonality, wind exposure, and drought tolerance to maximize performance year-round, especially in colder weather.

Cost: Green roofs can provide cost savings for a building’s heating and cooling. Construction costs of the green roof system are generally more expensive than typical roof construction and vary based on intensity and design. Maintenance costs are similar to landscape maintenance costs with occasional mechanical upkeep.

Maintenance: Regular maintenance activities include inspections, debris and sediment disposal, and frequent vegetation management.

 

Types of Green Roofs
NameVegetationMedia Depth
IntensiveSupports trees and shrubs10 or more inches
Semi-IntensiveGrasses, herbaceous perennials, and shrubs6-10 inches
ExtensiveSucculents, herbs, and grasses3-6 inches
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