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20.20.425 Hard surface.
A. Purpose. Limits on the total amount of hard surfaces associated with site development are desirable to minimize vegetation loss and limit stormwater runoff, which are impacted by the increased level of surface flow generated by hard surfaces. Live plant foliage and groundcover intercept stormwater by retaining or slowing the flow of precipitation to the ground, and their roots protect soil from erosion. Preservation of naturally vegetated areas is a passive stormwater management tool that effectively reduces watershed function deterioration.
B. Applicability. Hard surfaces are defined in Chapter 20.50 LUC, and shall include all surfaces considered impervious under LUC 20.20.460, as well as permeable pavement surfaces and vegetated roofs. The hard surface limits contained in LUC 20.20.010 and the standards of this section shall be imposed any time a permit, approval, or review including land alteration or land development including subdivisions, short subdivisions or planned unit developments, a change in lot coverage, or a change in the area devoted to parking and circulation is required by this Code, or by the International Building Code.
C. Exemptions. The following are exempted from determining maximum hard surface. These exemptions do not apply to any other Land Use Code requirement, including setbacks and limits on maximum lot coverage by structure, building code, utilities code or other applicable City of Bellevue codes or regulations.
1. Decks/Platforms. Decks and platforms constructed with gaps measuring one-eighth inch or greater between boards, so long as the surface below the deck or platform is pervious;
2. Rockeries/Retaining Walls. Rockeries and retaining walls shall be exempt from the maximum impervious surface limits;
3. Stabilization Measures. Shoreline stabilization measures shall be exempt from the maximum impervious surface limits; and
4. Landscape Features. Fences, arbors with lattice or open roof materials and similar structures, individual stepping stones placed in the ground but not cemented or held together with an impervious material, and organic mulch shall be exempt from the maximum impervious surface limits.
D. Performance Standards.
1. Design shall minimize topographic modification. Changes in existing grade outside the building footprint shall be minimized. Excavation shall not exceed 10 feet. Fill shall not exceed five feet subject to the following provisions: all fill in excess of four feet shall be engineered; and engineered fill may be approved in exceptional circumstances to exceed five feet to a maximum of eight feet. Exceptional circumstances are: (a) instances where driveway access would exceed 15 percent slope if additional fill retained by the building foundation is not permitted; or (2) where the five-foot fill maximum generally is observed but limited additional fill is necessary to accommodate localized variations in topography.
2. High-value natural areas, which include, but are not limited to, retained significant trees and their understory and areas of native vegetation, shall be identified during site development. Locations of buildings, roads and infrastructure shall not impact high-value natural areas. Retained significant trees and their understory and areas of native vegetation shall be fenced and adequately protected during construction, consistent with the provisions in Chapter 23.76 BCC. Native plants should be salvaged from areas to be cleared and transplanted to other areas of the site where feasible.
E. Maintenance and Assurance. Pervious pavement and other hard surface techniques designed to mimic shall be designed by a professional engineer licensed by the State of Washington and the plans are approved by the Director. The Director may require a maintenance plan and long-term performance assurance device to ensure the continued function of the pervious pavement or other technique. (Ord. 6323, 11-21-16, § 5)