I want to talk today about intensive green roofs. These roofs are beautiful but expensive due to their continued maintenance and irrigation requirements and structural requirements. In exchange for high cost a building owner gets a green roof that can have a large variety of plants ranging from flowers to tree. The soil is typically 8-24” deep and depends on the types of plants to be used. The roof systems are frequently used where they can be accessed by the public or where a building is designed to be tucked into the landscape.
The irrigation costs can be minimized through careful design. Buildings that are tucked into the natural landscape or higher rainfalls areas can often garner substantial irrigation cost savings. Additionally careful plant selection can minimize these costs so that only trees and large plants to require supplemental irrigation.
It is important to note that this system can weigh a lot – up to 200 psf! However, this can grant excellent thermal properties for the building. Buildings with green roofs typically have smaller internal temperature swings and lower heating and cooling costs.
An intensive green roof is typically going to consist of vegetation in a growing medium on top of a root barrier over a special drainage pan on rigid insulation over another root barrier over a waterproof roof membrane and the roof structure.
The BMW building in Dusseldorf, Germany and the Cultural Heritage Center in South Dakota are two excellent examples of intensive green roofs. The latter of which does not require additional irrigation.