Structural load capacity, how much weight the roof can hold, is a major factor in determining roof design and construction. Green roofs are therefore typically defined as being either extensive or intensive.
Semi-intensive green roofs represent a roof design intermediary between extensive and intensive roof. The following table summarizes characteristics of the different types of green roofs.
General characteristics of extensive and intensive green roofs (adapted from Green Roofs for Healthy Cities and the Cardinal Group, 2006).
Link to this table.
|Growing medium depth||6 inches or less||Portions of the green roof above and below 6 inches, with a minimum of 25% of green roof area above or below 6 inches||More than 6 inches|
|Accessibility||Often inaccessible||May be partially accessible||Usually accessible|
|Fully saturated weight||Low: 10 to 35 lb/ft2 (48.8 to 170.9 kg/m2)||Varies: 35 to 50 lb/ft2 (170.9 to 244.1 kg/m2)||High: 35 to 300 lb/ft2 (170.9 to 1464.7 kg/m2)|
|Maintenance||Varies, but generally lower than for intensive green roofs||Varies||Varies, but generally higher than for extensive green roofs|
|Stormwater management||Best cost-benefit balance||More growing medium and more vigorous plant growth provides marginally greater stormwater volume benefits||More growing medium and more vigorous plant growth provides marginally greater stormwater volume benefits|