Environmental Engineering Reference
In-Depth Information
5. Vegetated roof covers should incorporate internal drainage capacity suffi-
cient to accommodate up to a 2-year-return-frequency rainfall without generating
surface runoff flow.
6. Deck drains, scuppers, or gravel stops serving as methods to discharge
water from the roof area should be protected with access chambers. These enclo-
sures should include removable lids to allow ready access for inspection.
7. The design and layout should provide for maintenance access at least
around the roof perimeter and to other rooftop components (i.e., vents, HVAC
equipment, etc.).
8. The physical properties of the engineered media should be selected to
achieve the desired hydrologic performance and meet weight limitations.
9. Engineered media should contain no clay-size particles and should contain
no more than 15% organic matter (wet combustion or loss on ignition methods).
10. Media used in constructing vegetated roof covers should have a maximum
moisture capacity between 30 and 40%.
11. The irrigation system, if provided, should preferably consist of subsurface
drip or capillary mat water delivery, to minimize water loss by evaporation.
12. Plants should be selected that will create a healthy, drought-tolerant roof
cover (Figures 8-7 and 8-8). In general, several criteria should help guide species
selection for extensive vegetated roofs:
a. Native or adapted species tolerant of extreme climate conditions (e.g.,
heat, drought, wind; cold for high-elevation and far inland areas): a
“generalist.”
b. Low-growing, with a range of growth forms: spreading evergreen
shrubs or subshrubs, succulents, perennials, self-seeding annuals; note
Figure 8-7 Regency House, Washington, DC. (Courtesy of Roofmeadow, Inc.)
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