Extensive and Intensive Green Roofs

Extensive systems exist primarily for their environmental benefits and are not accessible rooftop gardens. They feature shallow soil or planting media, generally 2-6 inches deep. Vegetation consists of plantings such as sods and sedums with shallow root structures that can withstand harsh environments. The systems require little or no irrigation and typically need water only during the system’s start-up period. They can weigh 15-50 pounds per square foot.

Intensive systems offer both environmental benefits and accessibility. They feature deep soil or planting media, generally 9-18 inches deep or deeper. The root structure of vegetation, which can include trees and shrubs, varies. They can incorporate architectural features, such as paving, walkways, and benches, and they require irrigation. They typically weigh 80-150 pounds per square foot.

As with conventional roofing, the membrane of vegetative roof systems must slope to provide drainage. Although the membrane systems can withstand constant water exposure, it is a good practice to move water promptly away from roof details to reduce the potential for leaks.