Stormwater Quality Design Manual (May 2007) - City of Sacramento ...

Runoff Reduction Control Measure Fact SheetGreen RoofDescriptionPremier Automotive North American Headquarters, Irvine, CA.Photo: Roofscapes, Inc.A green roof is a multi-layered, vegetated rooftopsystem designed for filtering, absorbing, andretaining stormwater. Green roofs compriselightweight growth media and a specialized mixof vegetation underlain by a root barrier, adrainage layer, and a waterproofing membranethat protects the building structure. A green roofcaptures stormwater within the pore space of thegrowth medium and then releases the waterslowly via evaporation, transpiration anddischarge to the roof drains. There are two typesof green roofs—extensive (shallow growthmedia, simple vegetation) and intensive (deepergrowth media, complex vegetation).Siting Considerations• Space requirements; No additional space needed.• Land use: Most appropriate for commercial or multi-family land uses, particularly infilldevelopment and multi-story buildings in dense urban areas, parking garage and retail/warehouseroofs.Vector Considerations• Potential for mosquitoes due to standing water will be greatly reduced or eliminated if the greenroof is properly designed, constructed, and maintained.Advantages• Requires no additional land.• Improves outdoor air quality; aids in smog reduction.• Decreases roof and runoff temperature (heat island effect).• Provides insulation and lowers building cooling costs.• Protects underlying roof material from climatic extremes, ultraviolet light, and costlylong-term damage.• Can provide green space for building occupants to enjoy.• Provides habitat for wildlife, particularly birds.Limitations• Special structural design requirements to support green roof, irrigation needs and leak protectionelements (due to roof irrigation) are likely to increase building costs.• Erosion controls such as jute or cellulose netting and/or soil stabilizers will be required;additional controls such as cross-battens or steps may be required on sloped roofs.• General Maintenance Requirements (Moderate to High)• Irrigate to establish vegetation (first two years) and thereafter as needed.• Routinely inspect and maintain the roof membrane, drainage layer flow paths and irrigation system.• Repair eroded areas and replace vegetation as needed to maintain required cover.Stormwater Quality Design Manual for the Sacramento and South Placer RegionsMay 2007GR-1