Agenda - Planning Commission - 05/03/2012

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foundations rather than on fill is useful for floodwater storage. Local building codes may also require an increased elevation standard (freeboard) above the base flood elevation. This ensures that structures are elevated on properly designed and con- structed foundations and have the required flood openings and will result in lower flood insurance premiums. Furthermore, having a Building Code Effectiveness Grading Schedule classification of or better from the Insurance Services Office or having adopted all or part of the higher regu- latory standards of the International Building Code may be a vital tool in promoting flood resiliency in the community. Another source for more stringent building code requirements is the American Society of Civil Engineers' (ASCE) CONSERVATION SUBDIVISION STANDARDS In a conservation subdivision, the residen- tial density is typically the same or, in some cases, higher than in a conventional subdivi- sion. However, in a conservation subdivision the residential units are clustered together on smaller lots, leaving a large percent- age of the total site undisturbed. Steering development away from the floodplain and other environmentally sensitive areas of a site without reducing the potential density of the site can be a politically palatable way to reduce potential flood damage and help maintain flood storage and conveyance capacity. Consequently, many communities have adopted provisions sanctioning con- servation design in either their subdivision or zoning ordinances. Augusta's decisions to accept greenspace from conservation subdivisions are based, in part, on the city's community greenspace plan. The state of Georgia's Community Greenspace Program provides funding to help urban and rapidly developing cities and counties set aside zo percent of their land as permanent open space. As part of Augusta's participation in this program, the city has adopted a community greenspace plan that includes policies and specific proposals to provide permanent protection of environ- mentally sensitive areas. OVERLAY DISTRICTS Overlay districts superimpose additional regulations on underlying mapped zoning districts. Like conventional zoning districts, • Myrtle Beach uses its Coastal -Protection zoning overlayto lUmit new development seaward of the so year erosion control line. Flood Resistant Design and Construction standard (ASCE 24-05). ASCE 24-o5 requires a one -foot freeboard for most structures and up to three feet for critical facilities. Compliant building codes also • account for instability and decreased structural capacity associated with erosion, scour, and shoreline movement as part of foundation design for buildings in coastal areas and • prohibit construction of structures in certain high -risk areas such as alluvial fans, flash -flood areas, mudslide areas, erosion - prone areas, high -velocity -flow areas, and ice -jam and debris areas. Augusta, Georgia Augusta's zoning ordinance permits con- servations subdivisions in a number of low - density residential districts by right when all lots are at least 6o percent of minimum district lot sizes and by special exception when one or more tots are less than 6o per- cent of minimum district lot sizes. To qualify, the minimum tract size must be 20 acres and a minimum of4o percent of the overall acreage of the tract must be permanently protected as greenspace. The developer may either dedicate the greenspace to a public entity, a home owners' association, or a land trust, subject to approval of a green - space management plan by the city. overlays consist of both mapped boundaries and zoning text. The boundaries of an over- lay may not correspond to the boundaries of underlying zoning districts or even to parcel boundaries. For example, many communi- ties use zoning overlay districts to protect floodplains and riparian areas whose boundaries seldom follow property lines. Overlays in Vermont Communities in Vermont often use flood hazard districts to impose additional site and building standards for development located within a mapped flood hazard area. Similarly, a number of counties in Vermont use fluvial erosion hazard corridor overlay ZONINGPRACTICE 4.12 AMERICAN PLANNING ASSOCIATION I page 5