Garden Roofs Bring the Green
May 21, 2009
Today’s tip is about green, or garden, roofs.
There are two varieties of green roofs: intensive and extensive.
Intensive green roofs are the fancy kind, most often recognized as roof gardens that allow people to walk around and relax. They often include flowers, bushes, and even small trees. The largest intensive green roof in the world is Chicago’s Millennium park, a 24.5-acre green roof on top of two subterranean parking garages. Intensive green roofs are very heavy, ranging from 80 to 120 pounds per square foot saturated. They will usually only work for new construction, when the extra structure to support the weight can be engineered into the design of the building.
Extensive green roofs are usually less involved, with a thinner planting medium, and usually include smaller plants with shallower roots, like grass and flowers. They have a saturated weight of 12 to 50 pounds per square foot. The planting media is usually 1 to 5 inches thick. Several modular extensive green roof products have emerged in recent years, meaning that plants can be pre-grown in a factory and installed when needed – essentially an instant green roof.