4.7.4 Runoff Model Representation

Depending on local regulations, the modeling of a vegetated roof may result in a reduction in the size of downstream stormwater management facilities. General guidance for modeling vegetated roofs is provided below for two optional design configurations based on growing media depth:

Option 1 Design Criteria: 3-8 inches of growing media:
Represent the vegetated roof surface as 50 percent till landscaped area and 50 percent impervious area.

Option 2 Design Criteria: > 8 inches of growing media:
Represent the vegetated roof surface as 50 percent till pasture and 50 percent impervious area.

Consult local regulations to determine specific procedures to be used in modeling the hydrologic benefits of vegetated roofs and sizing downstream stormwater facilities.


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