Image credit: Green Roof Service, LLC
The waterproofing membrane has to be root resistant or has to be protected by a seperate root-barrier. The waterproofing membrane and root-barrier are seperated from the green roof components by a protection fabric weighing 15 to 27 ounces per square yard.
Serves the opposing functions of draining excess water and storing water for the roots to tap into in dry spells. It can take the form of inorganic granular media, dimpled plastic sheets, or ribbed fabric laminates. Seperation Fabric is installed above the drainage to keep soil from passing through and clogging.
The engineered soil contained in a green roof is made of lightweight aggregrate and organic matter. It must support plant growth, be lightweight, and must retain and drain water simultaneously. Standardized products with certified quality will be available.
The necessary plant characteristics for a green roof include plants that are regionally suited to withstand hot summers and cold winters, hardy and drought tolerant, produce a good ground coverage and are an aesthetically pleasing palette. In Central Pennsylvania, plants such as different varieties of Sedum and Delosperma, as well as certain perrenials and grasses work well.
The growing medium and plants are contained in plastic trays which are typically 2'x2' squares. Each tray is a self-contained unit and some types of trays create a grid-like appearance on the roof. Other trays have removable side walls allowing plants and media to co-mingle.