Greens roofs can cost more than traditional roofs but storm water runoff is reduced and the structure’s cooling costs are lowered. The heat island effect in cities are also reduced.
Intensive Green Roofs
Garden roofs, as they are commonly called, are Intensive green roofs. They are more complex than extensive green roofs. They have more plant diversity and experts say that more expertise is required to design this type of roof. Planting media for intensive green roofs needs to be at least a foot deep. Each square foot of the roof has to withstand 80 to 120 pounds of saturated weight. This depends on the type of plants and the planting medium. Intensive green roofs are almost always used for new constructions.
Extensive green roofs
More common are extensive green roofs. They have a saturated weight of 12 to 15 pounds per square foot. The planting media thickness is one to five inches. These green roofs are not designed for public use and they are not suitable for walking on. During the past few years, many modules have been emerged that allow planting to be grown in factories, before they are actually installed on a roof.
Although extensive roofs are lighter than intensive roofs, it cannot be assumed that they are a perfect fit for every roof. It is in fact wrong to assume that every roof can support a green roof; but it is worth mentioning that many structures will actually withstand a green roof without additional reinforcement.
What are the criteria for green roof capability?
The first step is evaluation of the structure. You must evaluate the structural loading capacity. If structural support is required, green roofs are not an economical choice.
What are the planting considerations?
Most expert’s advice is to use self-sustainable plants whenever possible. Similar to all landscaping projects, you need to make sure that the vegetation is appropriate for the location. The best solution is vegetation that doesn’t require irrigation.