11.07.080 Hillsides, Slopes, and Natural Grade

A. Slope analysis and natural grade. Slope analysis and natural grade shall be as determined by the “Interlaken Slope Study Map.” B. Boundary Delineation. A sensitive hillside or slope area shall be delineated where any slope is 25 percent or greater. C. Identification of Category of Use. Uses in the hillside areas shall be according to the following requirements: 1. Residential land uses shall be allowed on areas up to 30 percent slope if the development meets all the requirements of this Section. Slopes greater than 30 percent shall require a Special Hazard Study. 2. A geotechnical report is required for building on any slope over 10 percent. D. Grading, terracing, filling, benching and retaining wall considerations. The use of grading, filling, terracing or benching to either create or increase building lot size, or to modify building height objectives, is prohibited. However, the practice of excavating to “nest” the basement and better preserve the natural grade is encouraged, so long as the material excavated from the cut is not used to alter the rest of the existing grade, except as noted in this section. This concept notwithstanding, reasonable fill may be used within 30 feet of the dwelling to provide for driveways, parking, yard and public safety access. Grading in hillside areas shall be in accordance with Town standards. In order to preserve the sensitive lands throughout the Town, grading and filling permits and pre-inspections shall be required throughout the entire Town, regardless of slope. E. Retaining Walls. Retaining walls are discouraged, and the use of blended natural contours is encouraged. However, if it can be demonstrated by the applicant to the satisfaction of the Town Administrator, the Planning Commission, and the Town Council that there is no other alternative, then a retaining wall may be constructed in order to reduce the impact of cut banks and fill slopes of more than 6 vertical feet. Such retaining walls must be made of natural stone and blend into the colors and contours of the hillside. F. Exposed Concrete Walls. Exterior concrete walls which have more than six feet of exposed surface height, as measured from natural grade, in any section within the wall must be finished in accordance with standards set by the Town Administrator and Planning Commission, which may be updated from time to time. Acceptable finishes include: 1. Broom Finish 2. Stamped Concrete Finish 3. Exposed Aggregate Finish A separate review by the Planning Commission and Town Administrator shall be required for approval of any other type of exposed concrete finish. G. Allowable streets, driveways and grade crossings. The following restriction shall be placed upon the development of streets and driveways in a hillside sensitive area: 1. Maximum Grades. a. All streets shall be constructed at a maximum of twelve percent slope grade. Streets in grade between 10 percent slope and 12 percent slope shall be no more than 250 feet in length and only upon written approval from both the Town Engineer and Fire Marshal. b. Driveways to all residential dwellings shall be constructed at a maximum of 15 percent slope grade. However, driveways may be approved at a grade above 15 percent slope only if they receive written approval from the Town Engineer and Fire Marshal. 2. Criteria for Streets and Driveways Traversing Steep Slopes. All roads and driveways in hillside areas must receive full review from the Town Engineer, and final approval from the Town Council. Sensitivity to the landforms, erosion, plant life, wildlife and view shed are key considerations. Streets, roads, private access roads, driveways, and other vehicular routes shall not be allowed to traverse slopes between 25 percent slope and 50 percent slope unless specifically authorized by the Town Council upon recommendation from the Planning Commission. Any drive so authorized shall meet the following criteria: a. No alternative location for access is feasible or available. b. No individual segment of the street, road, private access road, driveway or other vehicular route that will cross slopes between 25 percent slope and 50 percent slope shall exceed 100 feet in length or, if greater than 100 feet, 10 percent of the total length of the street, road, private access road, or other vehicular route. c. No significant adverse visual, environmental, or safety impacts will result from the crossing. d. Fifty percent slope crossings. Unless a variance is granted, no street, road, private access road, driveway or other vehicular route cross slopes greater than 50 percent slope. e. Natural Contour. Streets, roads, private access roads, driveways and other vehicular routes shall follow the natural contour lines as much as possible. No street or road shall either traverse or follow a ridge or follow up a ridge line. 3. Grading for streets, roads, private access roads, and other vehicular routes shall be limited to the roadway portion of the right-of-way, plus up to an additional 10 feet on either side of the roadway as needed, except that when developing access on slopes in excess of 25 percent, only the roadway portion of the right-of-way shall be graded, plus the minimum area required for any necessary curb, gutter, or sidewalk improvements. The remainder of the access right-of-way shall be left undisturbed to the maximum extent possible. 4. Other Roads. Roads, other vehicle routes, or trails may be required to provide access or maintain existing access to adjacent lands for vehicle, pedestrians, emergency services, and essential service and maintenance equipment. 5. Shared Driveways. Driveways in sensitive land hillside areas may be shared by no more than four residential dwelling units or by four or more principal nonresidential uses, provided such nonresidential uses together do not exceed a total of 25,000 square feet of gross floor area. Shared driveways are strongly encouraged in these areas. 6. Restoration. All cuts, fills, berms, roadside grades or other disturbances created as a result of the road or driveway construction shall be protected from erosion and be restored to as natural a state as possible by restoration of natural vegetation. H. Landslide considerations. It is the intent of the Town that no construction shall occur in areas susceptible to landslides, nor shall any construction or disturbance create an area more susceptible to erosion or landslides or that will destabilize a preexisting landslide. Areas with potential for landslides may be identified on Town maps. The applicant is responsible to search for, perform studies that will identify, and disclose any information that is available to identify areas of instability. For all areas identified on Town materials as potential landslide areas, a slope stability analysis must be performed by a licensed geotechnical engineer before development is approved on those sites. The applicant, Planning and Engineering staff, the Planning Commission, and Town Council must then use this information to guide the development of the property. I. Maximum Height of Buildings. See Section 11.06.070 for this requirement. J. Exterior lighting. Floodlights shall not be used to light all or any portion of any primary or accessory structure facade. All outdoor light sources mounted on poles or buildings or trees to illuminate streets, sidewalks, walkways, patios, porches, parking lots or driveways or other outdoor areas shall use full cutoff fixtures. All such fixtures shall be installed or shielded so that the point light source or light bulb is not visible beyond the property boundary. Refer to Section 11.06.250 for additional requirements for outdoor lighting. K. Vegetation preservation and re-vegetation guidelines. All disturbed slopes of greater than ten per cent grade shall be re-vegetated with native plants and trees and properly maintained. L. Fire Protection. The following fire protection measures shall be taken when developments are placed in hillside areas: 1. Each development site and building permit shall comply with current fire regulations. 2. Spark arresters shall be installed in every indoor fireplace that burns solid fuel or wood. Screen openings in such arresters shall not be in excess of ¼-inch diameter. Outdoor wood-burning fire pits, fireplaces, chimneys, or other wood-based open flames are not permitted. Refer to Section 11.06.250 for more information about fireplaces, fire pits, and outdoor fires.