19.10.05 Hillside Development Guidelines

1. General Guidelines. A written statement addressing the following guidelines shall be submitted with the grading plan: a. Development shall be concentrated in the flattest areas of the site in order to preserve as much of the natural terrain as possible. b. Varied lot sizes and designs shall be utilized in order to reduce the amount of grading required and preserve natural landforms. c. Building pads shall be located in order to preserve as much of the natural terrain as possible. d. Lots and buildings shall be designed to fit the natural contour of the site rather than the site being altered to fit a particular structure type. e. Large flat pads shall be avoided in favor of stepped pads, or split-level structures that follow the general contours of the site. 2. Limits of Disturbance. No building or other structure is allowed on slopes greater than 30 percent. No excavation, grading, or permanent clearing shall be allowed on slopes greater than 30 percent, without the necessary plans and methods implemented as outlined in this Chapter. 3. Limits on grading. Grading shall comply with the following standards, in addition to the standards within other applicable Chapters: a. All cut, filled, and graded slopes and transitions shall be re-contoured to blend into the grade of surrounding land. b. The outside corners or edges of all permanent cut and fill slopes shall be rounded to eliminate sharp corners and shall have a minimum curvature radius of at least five feet. c. All permanent cuts and fills shall be constructed and stabilized to prevent settlement, sliding, and erosion. d. Mass grading and benching of hillside areas to create large flat building envelopes for multiple homes shall be avoided. Instead, smaller stepped envelopes for each home shall be used that follow the existing topography. e. Cut and fill slopes exceeding 50 percent shall be retained. f. The maximum slope of driveways shall not exceed 15 percent and shall minimize disturbance to natural terrain. g. Terracing shall be used to facilitate the completion of balanced cut and fill slopes as well as to reduce overall impacts to slopes. 4. Limits on changes to established lot grades. The elevation of an established lot shall not be permanently raised or lowered more than 6 feet at any point for construction of any structure or improvement, except: a. Areas outside the building pad but within the lot may be raised or lowered more than 6 feet if a retaining wall or other slope protection measure is used to reduce the steepness of man-made slopes, provided that the retaining wall complies with the provisions of this Chapter. 5. Limits on man-made slopes. a. Maximum cuts and fills shall not exceed 25 feet in height unless it is determined, per a geotechnical report, that the change in grade will restore the area and will improve the stability of a previously disturbed area. b. The grade of man-made slopes shall not exceed 50 percent without being retained. c. All cut, filled, and graded slopes shall be re-contoured and stabilized, as per this Chapter, to blend into the natural grade of surrounding land. d. All permanent fills shall be constructed and stabilized to prevent settlement, sliding, or erosion damage to streets, curbs, gutters, sidewalks, or buildings. 6. Terracing and retaining walls. Use of retaining walls is encouraged to reduce the steepness of man-made slopes as outlined herein. Cutting terraces combined with the use of retaining walls may be implemented to create buildable areas, to minimize or alleviate potential erosion to hillsides, and to establish planting pockets conducive to revegetation of hillsides. The following standards shall apply: a. Individual retaining walls may be permitted to support steep slopes but shall not exceed 10 feet in height measured from adjacent finished grade. b. When the overall retained height would exceed ten feet, the retaining wall shall be segmented into a maximum of three stepped walls with no individual wall exceeding six feet in height as measured form the lowest adjacent grade to the top of the wall. c. Retaining walls taller than 4 feet shall be separated from any other retaining wall by a minimum distance of 3 horizontal feet or half the height of the highest wall, whichever is greater. Terraces created between retaining walls shall be permanently landscaped or re-vegetated per City Code. d. A building permit shall be obtained if required by the Building Code. The lot owner or developer may be required to obtain documentation from the building official that a building permit is not required. e. The parabolic slip plane mode of failure of the retaining wall system shall be used to determine height and wall separation. (See Figure 10.1.) Figure 10.1 7. Structures. Additional grading for structures shall be determined on an individual lot basis, shall be minimized by designing the house to fit the natural slopes, and shall meet the following requirements: a. The general location and magnitude of cuts and fills shall be identified with each site plan. b. Where building masses orient against the lot’s existing contours, the structures shall be stepped with the grade and broken into a series of individual smaller components. (See figures 10.2 & 10.3 below) c. Structures and foundation types shall be utilized that are compatible with the existing hillside conditions and require less grading. Split-level, embedded structures, and stepped foundations shall be utilized. (See figures 10.2 & 10.3 below) d. Building height shall comply with the requirements in the specific zone using the definition in 19.02. e. No more than four feet of the foundation may be exposed on the fronts of the structure and no more than six feet on the sides and backs of the structure. Figure 10.2 Figure 10.3 8. Preservation of existing vegetation. Existing concentrations of significant trees and vegetation shall be preserved, except that noxious or invasive trees and vegetation and sage brush are not required to be preserved. a. For the purposes of this subsection, “significant trees and vegetation” means: i. Large trees of 6-inch caliper or greater; and ii. Groves of five or more smaller trees, or clumps of shrubs covering an area of 50 square feet or more measured at the drip lines. b. Areas with significant trees and non-invasive vegetation may not be disturbed unless specifically approved by the City, based on a replacement plan as described in Chapter 19.06. 9. Revegetation. a. Any permanent slope exposed or created in new development shall be landscaped or revegetated with native or adapted trees and other native or adapted plant material. b. New vegetation shall be equivalent to, or exceed, the density and erosioncontrol characteristics of the original vegetation cover to mitigate adverse environmental and visual effects. c. All existing native or adapted vegetation within and adjacent to major drainage channels shall be preserved to the maximum extent practical. d. All areas of the site where removal of native or adapted natural vegetation in the course of development will occur shall be replanted with native or adapted trees and plants. The vegetation shall possess erosion control characteristics (such as fast growing and deep roots) at least equal to the native or adapted vegetation which was removed. These may be replaced within other areas of the site such as open space, common areas, or street trees. e. Use of fire-resistant plants for revegetation is strongly encouraged and shall be required if the area is located in a Wildland-Urban Interface area per the City’s Fire Code. (For a list of fire-resistant plants, refer to the Wildland-Urban Interface, contact the local Forest Service, or contact the Utah Division of Forestry, Fire, and State Lands.) f. All disturbed areas shall be stabilized no later than 30 days after the disturbance is complete. Reseeding may be delayed until the earliest planting season thereafter if temporary stabilization measures are implemented in the interim. 10. Buildable Area and Limits of Disturbance. a. Slopes greater than 30 percent shall be identified on the plat and restricted on the plat as protected, undisturbed areas. A lot may contain existing natural grades in excess of 30 percent if the following conditions are met: i. The subdivision plat clearly identifies the limits of disturbance and each lot contains a buildable area that is: 1. at least 2000 square feet of contiguous area; 2. a minimum dimension of 30 feet in any direction; 3. no greater than 30 percent in slope; and 4. contained within the building setbacks of a proposed lot. ii. Slopes greater than 30 percent shall be recorded on the plat or site plan with a prohibition on their disturbance. iii. No grading, building, accessory building, or structure will be allowed outside of the limits of disturbance as delineated on the respective plat or site plan. iv. Access and driveways shall be included within the limits of disturbance for a lot. v. No grading related to the construction of the structure shall occur outside the limits of disturbance. b. The buildable area and limits of disturbance must be recorded on the plat along with an easily identified location for clear access. 11. Streets and hard surface trail access and driveways. a. Streets and hard surface trails and driveways may cross slopes over 30 percent and up to 50 percent if deemed necessary by the Development Review Committee (DRC). Approval shall be based on the following findings: i. No alternate location for access is feasible or available. ii. No individual segment or increment of the street or trail crossing these slopes exceeds 1500 feet in length. iii. Visual, environmental, and safety impacts from the street or trail crossing shall be mitigated as outlined in the revegetation, grading, and erosion sections of this chapter. c. The developer shall dedicate to the City a slope easement for any cut or fill slope created by construction of a street on a hillside which is not contained within the public right-of-way to allow for future road maintenance or reconstruction of the road. d. Points of access shall be provided to all developed and undeveloped land for emergency firefighting equipment. e. Emergency vehicle access shall be provided to trails in canyons, drainages, and natural washes shall be provided for developments that are located adjacent to such canyons, drainages, or washes. f. When open space, common area, or undeveloped land is behind lots, access between homes is required every 1000 feet for emergency access. g. Private driveways that are longer than 150 feet shall not exceed a grade of 10 percent at any point, so as not to hinder emergency service vehicles. h. Driveways longer than 150 feet shall require a fire truck turn around. i. Access via streets and driveways require approval by the Fire Chief and shall comply with the Fire Code. 12. Drainage corridor and flood zone protection. a. Filling and dredging. Filling or dredging of natural drainage channels as identified for protection by the City shall meet Engineering Standards. b. Minimum setbacks. Lots shall be setback 20 feet horizontally from the top of the required freeboard, whether ephemeral or not, of: (a) water courses; (b) gullies; and (c) major drainages as identified for protection by the City as open channels in the Storm Drain Capital Facilities Plan. 13. Responsibility for construction and maintenance of improvements. The developer shall be fully responsible for making all improvements in accordance with accepted plans.