What are the different types of Green Roof?

Green roofs are classified as either extensive or intensive. Extensive green roofs are lightweight and low maintenance. They are usually inaccessible and are therefore planted with drought-resistant species, which survive on rainwater. Intensive green roofs require comprehensive maintenance. Because intensive green roofs are often accessible and more elaborately planted, buildings must be able to bear extra weight. Issues of irrigation, fertilization, pest control, and plant selection are also more complex.