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

Technical RequirementsGreen RoofGrowth media need to remain viable for decades for both plant growth and water control. Thegrowth medium used in green roofs should:• Not degrade or compress over time;• Be accompanied by third-party laboratory data confirming its essential properties; and• Be covered under warranty if it is defective or degrades within a certain timeframe.Gravel Ballast (if needed) — Gravel ballast is sometimes placed along the roof perimeter and atair vents or other vertical elements. The need for ballast depends on operational and structuraldesign issues. Ballast is sometimes used to provide maintenance access, especially to verticalelements requiring periodic maintenance. In some situations a header or separation board may beplaced between the gravel ballast and adjacent elements (e.g., growth media, drains). If a rootbarrier is used, it must extend under the gravel ballast and growth medium and up the side of thevertical elements.Step 6 – Select VegetationHire experienced horticulturists and/or landscape/green roof contractors who understand the local climateas well as the restrictions of a rooftop environment to select, install and maintain vegetation for the greenroof.Typical green roof vegetation ranges from low-growing succulent plants (e.g., sedums) or groundcovers(characteristic of extensive green roofs) to an assortment of native grasses, shrubs, and trees (more typicalof intensive green roofs). Select plants that:• are adapted to the local climate, considering seasonal temperature ranges and average rainfall, theharsh rooftop environment (exposure to direct sun, frost, wind) and desired irrigation• will tolerate short periods of inundation from storm events during the wet season (October 1 –April 30)• Possess shallow root systems suited for the depth of the growth media• Require little or no irrigation after establishment• are primarily non-deciduous to provide adequate foliage cover year-round and reduce erosionpotential• Have good regenerative qualities (i.e., perennial or self-sowing)• Are low maintenance (i.e., no need for fertilizers, pesticides, or herbicides, little or no mowing ortrimming)• Have growth patterns allowing vegetation to thoroughly cover the soil (at least 90% surface areacoverage should be achieved within 2 years).• Are compatible with the aesthetic preferences of the owner and future building occupants whomay utilize the roof as a green spacePlants of the genus Sedum (family Crassulaceae), which are low-growing succulents, are often used forbecause of their resistance to wind, frost, drought, and fire. A mix of Sedum and other succulent plants isrecommended, because they possess many of the recommended attributes. Herbs, forbs, grasses, and otherlow groundcovers may also be used but typically require more irrigation and maintenance. Although theuse of native vegetation is preferred when possible, some natives may not thrive in the rooftopenvironment. Thus, a mix of approximately 80% Sedum/succulent plants and 20% native plants generallyrecognized for their hardiness is recommended, particularly for extensive green roofs. (Velazquez, 2005)Stormwater Quality Design Manual for the Sacramento and South Placer RegionsGR-6 May 2007