Green Roofs "Roofs for the Future"

What are the most important factors in designing a green roof?

There are many complex, interactive factors that green roof design engineer takes into account, balancing many considerations for optimal performance, including:

•  Climate, especially temperature and rainfall patterns
•  Strength of the supporting structure
•  Size, slope, height, and directional orientation of the roof
•  Type of underlying waterproofing
•  Drainage elements, such as drains, scuppers, and drainage conduits
•  Accessibility and intended use
•  Visibility, fit with architecture, and owner's aesthetic preferences
•  Fit with other 'green' systems, such as solar panels
•  Costs of materials and labor
 
What is the difference between an 'extensive' and an 'intensive' green roof?

There is no strict demarcation. Generally speaking, 'extensive' green roofs are less than 6 inches deep, and, depending on depth, may support a range of plants, such as Sedums (low-growing succulents), herbs, meadow grasses, and perennials. Deeper 'intensive' systems can sustain complex landscapes, including small trees and even small ornamental ponds and fountains.
 
How much does a green roof weigh?

Green roofs vary greatly in weight, depending on their depth and the material components. The important measurement is 'wet' weight -- fully-saturated fabrics and plants. For example, Roofmeadow® systems, engineered to be both lightweight and efficient, generally weigh about 6.75 pounds per square foot for each inch of depth. Thus, the saturated weight of a 2-inch deep system is about 13 pounds per square foot, including a mature plant cover. Mid-range, 5-inch, systems weigh approximately 34 pounds per square foot and are compatible with wood or steel decks. 'Intensive' systems weigh 36 pounds or more, and generally require a concrete supporting deck

This type of roofing is fairly new and anyone who is interested should research this further, and find a contractor that specializes in Green Roofs.