WiserEarth Governance

Green roofs, also known as vegetated roof covers or eco-roofs, are thin layers of living vegetation installed on top of conventional flat or sloping roofs. Green roofs protect conventional roof waterproofing systems while adding a wide range of ecological and aesthetic benefits. They are a powerful tool in combating the adverse impacts of land development and the loss of open space.

Green roofs are divided into two categories: 1) extensive green roofs, which are 6 inches or shallower and are frequently designed to satisfy specific engineering and performance goals, and 2) intensive green roofs, which may become quite deep and merge into more familiar on-structure plaza landscapes with promenades, lawn, large perennial plants, and trees. This guide addresses only the more shallow extensive green roofs.

The challenge in designing extensive green roofs is to replicate many of the benefits of green open space, while keeping them light and affordable. Thus, the new generation of green roofs relies on a marriage of the sciences of horticulture, waterproofing, and engineering.

The most common vegetated roof cover in temperate climates is a single un-irrigated 3- to 4-inch layer of lightweight growth media vegetated with succulent plants and herbs. In Germany, this simple design has demonstrated the highest benefit-to-cost ratio. In most climates, a properly designed 3-inch deep vegetated roof cover will provide a durable, low maintenance system that can realize the many benefits that green roofs have to offer.