Green Roofs

Types of Green Roofs

There are two main kinds of green roofs: intensive and extensive. The difference depends largely on the amount of maintenance they need and the depth of the planting medium used. Intensive green roofs tend to have deeper planting media as well as contain complex irrigation systems. Intensive green roofs generally include a broad range of ornamental plant species and large plants such as trees and shrubs, and they may have ponds and other decorative features. Intensive roofs are the most expensive kind of green roof. The roofs they are built on must be engineered to accept the weight of deep soil and large plants. Their need for ongoing maintenance also adds significantly to the long-term labor costs of the roof. Intensive green roofs have a greater emphasis on aesthetics than extensive roofs and are usually designed for public access and recreational use.

Extensive green roofs, which have lower construction and maintenance costs than intensive roofs, are the more common kind of green roof. They generally have a thin, lightweight growing medium, which lowers the weight load that the building must handle, allowing this type of green roof to be built on a larger variety of structures. The lightweight planting media, along with a lack of irrigation other than rainfall, requires that the plants on these roofs be chosen for their hardiness and drought-resistant properties, such as sedum. These features, along with ease of maintenance, are generally considered more important than the plants’ aesthetic appeal. Extensive green roofs are designed to be virtually self-sustaining and to require only a minimum of maintenance. They are generally accessed only for maintenance and not for recreational purposes.

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