Green roofs are structurally engineered and generally comprise of six key components as illustrated in the figure bellow. These are:
- The uppermost planted layer. Success of any green roof depends on how healthy the plants are.
- The growth substrate which is the growing media and directly influences the plant growth and performance of green roofs.
- The filter layer which prevents small media particles (i.e. soil fines, plant debris) from blocking the drainage layer below.
- The drainage layer which provides an optimal balance between water and air in the system. It is a key component affecting the amount of storm water which will be retained on the roof at any given time. It aids in the removal of excess water from the substrate and also improves the thermal properties of the roof.
- The protection layer or protection mat which is used to protect the waterproof membrane from damage following installation. Usually, the protection layer is installed directly on the waterproofing layer or at the top of the root barrier layer, providing further protection against root penetration and doubling as a separation sheet.
- The root barrier which protects the integrity of the roof from roots of plants that could penetrate from green roof’s upper layers. It protects the structure from damage.
- The waterproof layer and the insulation are, of course, vital parts of any roof. Besides that, there are some additional components depending on the climatic conditions like irrigation systems.
Cross section of a green roof (Source: Ahmet B.Besir, Erdem Cuce. Green roofs and facades: A comprehensive review. Renewable and Sustainable Energy Reviews, Volume 82, Part 1, February 2018, Pages 915-939)