Green roofs can be classified by their purpose and characteristics
in to two major types: intensive roofs and extensive roofs
[8,51]. Intensive roofs need a reasonable depth of soil and require
skilled labor, irrigation, and constant maintenance. They are usually
associated with roof gardens [20]. Extensive roofs have a relatively
thin layer of soil, grow sedums and moss and are designed to be
virtually self-sustaining and require minimum maintenance [20].
There is a third type of green roofs called semi-intensive. Semiintensive
green roof is a combination of extensive and intensive,
however the extensive type must represent 25% or less of the total
green roof’s area [51].