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1. Purpose And Intent: To development of hillsides and foothills is consistent with the Boise City Comprehensive Plan and to ensure protection from hazards due to slope, erosion-prone soils, unstable soils, earth movement, and other geologic and hydrologic hazards.
2. Applicability: These provisions shall apply to development on properties where the slope exceeds 15 percent or where adverse conditions due to slope stability, expansion soils, high water table and springs, erosion, or sedimentation are present as determined by the Director or City Engineer.
3. Categories Of Hillside Development Permits: The director (with input from the City Engineer) shall determine whether an application may be processed as a Category I, II, or III permit.
A. Category I: Category I permits are issued by the Director for minor, routine construction on prepared building pads and single-lots that do not involve significant grading. For example:
(1) Single-family residential homes or accessory structure placed on lots needing little modification, in a development for which a Category III permit has previously been issued.
(2) Single-family residential homes or accessory structures, placed upon lots of record that; comply with approved building envelopes and limits to grading; and, for which Category II permit criteria are not exceeded.
B. Category II: Examples of the development requiring a Category II permit are:
(1) Exterior additions to existing structures; or
(2) Grading with significant modification of approved topography; including:
(a) A retaining wall which is greater than four feet of exposed height or more than one retaining wall when the horizontal distance between retaining walls is less than ten feet and the total of all exposed retaining walls exceeds four feet in height.
(b) An excavation or fill which exceeds the limits as defined International Building Code Chapter 18 and Appendix J as amended by Boise City Code Chapter 9-1.
(3) Access roads or driveways in excess of 100 feet in length or in excess of 15 Percent grade. Such driveways shall be reviewed for impacts on drainage and soil stability, emergency access, access to the public street and potential physical impacts on neighboring properties.
(4) Multiple retaining walls located within setbacks, per Section 11-07-05.4, Retaining Walls.
C. Category III: Category III permits are for PUDs, preliminary subdivision plats, or grading involving modification of approved topography beyond that allowed under Categories I and II, including:
(1) Projects where the Director, with input from the City Engineer, determines that slope stability or drainage problems exist.
(2) Projects involving modification of pre-graded lots in excess of 30 percent of the volume of previous excavation or fill or 30 percent of the surface area by square footage.
(3) Projects involving modification of lots with natural topography in excess of 30 percent of the surface area of the lot.
(4) Projects not defined as a Category I or II but that fall under the purview of this chapter.
4. Hillside Development Restrictions: Any area that presents one or more of the following limiting factors shall not be subject to development unless the project engineer can demonstrate satisfactorily to the City Engineer, based on the required technical reports, that these site limitations can be overcome in such a manner as to minimize hazard to life, hazard to property, and adverse effects on the safety, use, or stability of a public way or drainage channel. Such site limitations to be overcome shall include but not be limited to the following:
A. Landslide areas or scarps, or areas of active landslides.
B. Lines of active faults.
C. Areas with expansive soils or collapsible soils.
D. Slopes greater than 25 percent.
E. High water table and springs.
5. Hillside Development Standards:
A. Standards Applicable To All Categories Of Hillside Development Permits:
(1) Planning of development shall account for the topography, soils, geology, vegetation, outstanding features such as outcropping and cliffs, hydrology and other conditions existing on the proposed site.
(2) Development shall be oriented on the site so that grading and other site preparations are kept to a minimum.
(3) Essential grading shall be completed during site preparation, rather than left for future lot owners so that:
(a) Shaping shall blend in with existing topography to minimize the necessity of padding or terracing of building sites; and
(b) Building pads and terracing shall be graded to blend into the natural contours.
(4) Paving shall be completed within 60 days after final grading (final grading any grading done after the placement of utilities).
(5) Areas not well suited for development because of soil, geology, vegetation, or hydrology limitations shall be reserved for open space.
(6) Disruption of existing plant and animal life shall be minimized.
(7) Innovative methods of slope and soil stabilization, grading, and landscaping are encouraged.
(8) Multiple access points and street grades that meet requirements of the Fire Department and ACHD shall be provided.
(9) Pedestrian access to and through the project shall be provided.
(10) Conformance Bond and Surety: A bond and surety agreement or an irrevocable letter of credit in an amount of 110 percent of the cost estimated by the City Engineer is required to enable restoration of the site if the project is not completed as approved. The bonding shall be provided prior to the issuance of a grading permit or signing of the final plat by the City Engineer.
(11) Prior to issuance of a grading permit, the owner and/or developer shall provide a legally binding easement allowing the City of Boise and/or its agents to enter upon the property to do work, as deemed necessary by the City Engineer, to restore the site's appearance and drainage in case of non-completion or substantial deviation from the approved plans of the project by the developer/owner.
(12) All work must be performed in accordance with the latest approved contract plans and specifications. Work not in accordance may not be accepted. Revisions to the plans and specifications shall be submitted to the City Engineer and Planning Director, allowing sufficient time for review, comment, revision and approval.
B. Grading Standards:
(1) No grading, filling, clearing, or excavation of any kind in excess of 50 cubic yards or stripping of vegetation shall be initiated until the required final grading plan is approved by the Public Works Department and a grading permit is issued.
(2) Fill areas shall be prepared by removing any organic material that is determined by the geotechnical report to be detrimental to proper compaction or otherwise not conducive to stability.
(3) Borrowing for fill shall be prohibited unless the material is obtained from a cut permitted under an approved grading plan or imported from outside the hillside areas of Ada County. No cuts shall be permitted solely for the purpose of obtaining fill unless approved in the grading plan.
(4) All retaining walls higher than four feet shall be engineered so that structural members are keyed into stable foundations and are capable of sustaining the design loads.
(5) Fills shall be compacted to at least 95 percent of maximum density, as determined by AASHTO T-99, ASTM D-698, ASTMD-1557 or greater as recommended by the geotechnical report. The frequency of compaction testing shall be addressed in the geotechnical report and shall be approved by the City Engineer.
(6) Cut slopes shall be no steeper than two feet horizontal to one foot vertical unless it can be shown by the project geotechnical engineer that steeper slopes are feasible, taking into account safety, stability, erosion control, and re-vegetation. For cut slopes steeper than two feet horizontal to one foot vertical, subsurface drainage shall be provided as necessary for stability.
(7) Fill slopes shall be no steeper than two feet horizontal to one foot vertical unless it can be shown by the project geotechnical engineer that steeper slopes are safe, stable, erosion resistant, and can be adequately re- vegetated. Fill slopes shall not be located on natural slopes two to one or steeper, or where fill slopes toe out within 12 feet horizontally of the top of an existing or planned cut slope.
(8) Prior to placement of fill, the ground shall be prepared in accordance with the International Building Code Chapter 18 and Appendix J as amended by Boise City Building Code Chapter 9-1. Subsurface drainage shall be provided as necessary for stability.
(9) Tops and toes of cut and fill slopes shall be set back from property boundaries in accordance with the requirements of the International Building Code Chapter 18 and Appendix J as amended by Boise City Building Code Chapter 9-1.
C. Re-Vegetation And Erosion Control Standards:
(1) Vegetation should not be disturbed beyond the limits of the approved grading plan.
(2) Topsoil removed during construction shall be conserved for later use on areas requiring re-vegetation or landscaping.
(3) Topsoil shall be placed at a minimum thickness of four inches.
(4) The minimum acceptable plant coverage is 80 percent two years after planting.
(5) Seed mix shall include deep-rooted plants and subsequent planting of seedlings.
(6) Erosion shall be controlled to prevent deposition of sediment on adjacent property.
D. Hydrologic Controls:
(1) Interceptor ditches or other methods approved by the City Engineer shall be established above all cut or fill slopes, and the intercepted water shall be conveyed to a stable channel with adequate capacity. Provision for ditch maintenance must be approved by the City.
(2) Curb, gutter and pavement design and lot grading shall be such that water on roadways is prevented from flowing off roadway, except in conveyance conduits.
(3) Natural stream channel shall be stabilized using a method acceptable to the City Engineer.
(4) Runoff from areas of concentrated impervious cover such as roofs, driveways, and roads shall be retained on- site or collected and transported to a channel with sufficient capacity to accept the discharge without erosion or flooding. Provision should be made by the owner or developer for the cleaning of drainage facilities from the onset of construction through the completion of the project.
(5) Waste material from construction, including soil and other solid materials, shall not be deposited within the 100-year flood plain unless the City Engineer concurs that there is no reduction in storage and flow capacity of the flood plain.
(6) Drainage systems shall be designed to accommodate a 100-year flood event.
(7) With the exception of road crossings, approved drainage structures, and recreation and open space uses that do not involve the destruction of vegetative cover, development shall be prohibited within the 100-year floodway.
(8) Sediment catchment ponds shall be constructed and maintained downstream from each development unless sediment retention facilities are otherwise provided. Any facility used shall provide for the removal of surface debris and contaminants, as well as sediment retention. The facilities shall be designed to facilitate maintenance at minimal cost. Each completed phase of a drainage system shall be designed for the 100-year occurrence.
(9) The overall drainage system shall be completed and made operational at the earliest possible time during construction.
(10) Alterations of major floodways shall only be made with approved drainage conveyance systems and structures as approved by the City Engineer, Army Corps of Engineers, and FEMA.
(11) Natural streams or improved open channels shall be preserved or provided for in major (ten acres or larger)catchments except where otherwise approved by the City Engineer. In minor catchments, drainage shall be permitted to be enclosed in conduits.
(12) Flow rates from a newly developed site shall not exceed the flow rate from the site in its natural condition prior to development. Exceptions shall be appropriate if compliance with the prior sentence creates more adverse impacts to the overall drainage area than other drainage alternatives.
(13) Drainage facilities shall be designed to coordinate with any Master Drainage Plan for the drainage basin in which the proposed development is located.
(14) Special drainage facilities or an overflow path for floodwater shall be designated in all locations where there is a sag in the profile of the street or at the end of a cul-de-sac that is lower than the intercepting street. Restriction shall be placed to protect the overflow path from the future building of any fence, shed, dwelling, or obstruction that would impede the flood flow.
E. Roadways And Circulation:
(1) Roads shall be designed to minimize land coverage and soil disturbance.
(2) Existing deep-rooted perennial vegetation shall be preserved to the extent possible.
(3) Variations in road design and construction and right-of-way requirements shall be sought through ACHD in order to keep grading and cut or fill slopes to a minimum.
(4) Road alignments should follow natural contours; cul- de-sacs and common driveways are encouraged.
(5) One-way couplets shall be encouraged where appropriate for the terrain and where public safety would not be jeopardized. Road width shall be a minimum of 20 feet to allow the passage of emergency vehicles.
(6) If the sidewalk is to be installed parallel to the roadway on fills, the slope shall be rounded for four feet from the back of the sidewalk.
(7) A pedestrian pathway shall be required as approved by the PZC. (See 11-07-04.4, Pedestrian Access.)
(8) Combinations of collective or common private driveways, cluster parking areas, and on-street parallel parking bays shall be used where possible to attempt to optimize the objectives of minimum soil disturbance, minimum impervious cover, excellence of design, and aesthetic sensitivity.
F. Maintenance: The owner of any private property on which grading or other work has been performed pursuant to a grading plan approved under the provisions of the this Section, or a building permit granted by the Development Services Department, within a subdivision approved under the provisions of this Section 11-07-08, Hillside and Foothill Development Standards, shall maintain in perpetuity and repair all graded surfaces and erosion prevention devices, retaining walls, drainage structures, means, or devices deemed not to be the responsibility of the ACHD or other public agency, and plantings and ground cover installed or completed. Such requirements shall be incorporated into the protective covenants for any subdivision or development.
G. Waivers: The developer, the project engineer, or the developer's representative may request a waiver of any of the provisions of this Section. The request shall be made to both the Director and the City Engineer. The Director and City Engineer shall notify the public of the request for waiver in accordance with Section 11-03-03.4, Step 4: Notice. After public notice and comment on the waiver request, the City Engineer and Director will review and decide on the proposed waiver. The decision may be appealed to the Council.
H. Inspection And Enforcement:
(1) All construction subject to these regulations shall be subject to inspection by the City Engineer and Planning and Development Services Department in addition to inspections by the Project Engineer and consultants. When required by the City Engineer, special inspections and special testing shall be performed to verify conformance with these regulations. The cost of special inspections and special testing shall be borne by the developer.
(2) If the City Engineer determines that any portion of the project is not in conformance with the requirements of this Chapter and no waiver of such requirements has been granted, the City Engineer shall notify, in writing, the Project Engineer and/or Developer. The Project Engineer and/or Developer shall take prompt action to resolve the problem(s) enumerated. If corrective action is not taken to the satisfaction of the City Engineer then the City Engineer shall cause a stop work order be issued by the Planning and Development Services Department, notify the agency issuing the bond or irrevocable letter of credit, shall cause the necessary work to be performed at the developer's expense, not sign the final plat, cause the Planning and Development Services Department to not issue any additional building permits for this development and/or collect on the bond or irrevocable letter of credit.
6. Application Procedure: A hillside and foothill development permit may be obtained by submitting an application(s) in one or two stages as follows:
A. As a detailed hillside and foothill development plan, on an application form to be provided by the Planning Director and including all information required by this chapter.
B. As a conceptual master plan.
(1) The applicant must specify on the application form that concept approval is being requested and must be accompanied by a request for rezoning if the land is not zoned for the intended use. A concept approval is a statement by the City of Boise that a general development plan including the general arrangement of uses, density, location of major streets, open spaces, utilities, etc. is acceptable. A concept review allows the applicant to obtain approval of a general development plan without incurring the expense of preparing detailed building plans until after the concept approval. It provides the developer and the City with guidelines for the design of each phase of a project. Supporting information shall be required for concept applications as determined by the Planning Director.
(2) A concept plan which falls under the purview of this section will by its nature require more detailed engineering studies than concept plans in less sensitive areas. Therefore, at least generalized plans for drainage, grading and utility service shall be provided with the application.
(3) Each phase of a concept approval requires detailed hillside and foothill development approval through a new application, fee and public hearing. Conditions attached to applications for detailed hillside and foothill approval shall not exceed the parameters of the conditions of approval attached to the concept plan so long as the concept plan has not expired. Submittal requirements are the same as for a detailed hillside and foothill development application that is processed and reviewed in one step.
C. Hearings: The concept and detailed Hillside and Foothill Development applications are both subject to the public hearing requirements of Section 11-03-04.17.
D. The requirement for a public work session on phases of a conceptual master plan may be waived by the Planning Director if:
(1) The detailed submittal conforms to the approved concept plan.
(2) The phase of the project involves development on slopes less than 15 percent.
7. Term Of Permits:
A. Due to the special problems related to hillside developments, the applicant or developer shall have 36 months in which to affect a hillside and foothill development permit after approval by the PZC. Within this period, the holder of the permit must:
(1) Acquire construction permits and commence placement of permanent footings and structures on or in the ground. The definition of structures in this context shall include sewer lines, water lines, streets, or building foundations;
(2) Commence the use permitted by the permit in accordance with the conditions of approval;
(3) For conceptual hillside and foothill development permits, submit an application for a detailed hillside and foothill development permit; or
(4) For projects which require platting, the plat must be recorded within this time frame.
B. For phased projects each phase must be submitted within 24 months from the date of the concept approval or the date of approval of the previous phase, unless the PZC specifically approves a different phasing schedule.
C. The PZC may also fix the time or period within which the permit shall be completed, perfected, or bonded. If the conditions of approval are not completed or bonded within such period, said permit shall lapse.
D. Extensions:
(1) The PZC may, upon written request by the holder, grant a one-year time extension to an unexpired conceptual or detailed hillside and foothills development permit.
(a) A maximum of three extensions may be granted to initiate the project or a phase of a project.
(b) Additional conditions of approval may be required based upon the existence of legal requirements not existing at the time of the original approval.
(2) Upon receipt of written request for extension, the Director shall determine if a hearing on the request is required, based on the following considerations:
(a) Detailed Permits:
i. Whether there have been significant amendments to the Boise City Comprehensive Plan or Title 11, Boise City Code, which will apply to the subject permit;
ii. If significant land use changes have occurred in the project vicinity which would adversely impact the project or be adversely impacted by the project;
iii. Whether hazardous situations have developed or have been discovered in the project area; or
iv. If community facilities and services required for the project have become inadequate.
(b) Conceptual Master Plans: Concept plans are encouraged to facilitate good planning in the Boise foothills. Developers must have some assurance that concept plans that have been initiated in accordance with existing ordinances and conditions of approval may be completed under the originally applied standards. Therefore, approved conceptual master plans will not be subject to new ordinance requirements if the following findings are made:
i. The applicant has made significant on- and off- site improvements that implement the overall plan such as the extension or on-site installation of water mains, sewer lines, streets, and utilities;
ii. If development of previous phases of the plan have occurred in such a manner that it is physically impossible or economically unfeasible to comply with the new ordinance standards;
iii. The applicant demonstrates that application of the new standards will make it impossible or totally unfeasible to complete the remaining phases of the concept plan; and
iv. If any of the considerations in i, ii, or iii above are found to exist with regard to the project for which an extension is sought, a hearing shall be required.
(3) If a hearing is required, notice shall be provided as described in Section 11-03-03.4 of this Code and a new application and fee must be submitted in compliance with current plans and ordinances and in accordance with the application procedures of this chapter.
8. Modification And Revocation:
A. Upon application by the holder of a hillside and foothills development permit, the PZC may modify the conditions and limitations of the permit in accordance with the limitations and requirements of Section 11-03-04.17. The PZC may revoke or modify a hillside and foothills development permit, upon notice and hearing, for breach or violation of any condition or limitation of said permit.
B. Administrative Review Of Minor Modifications:
(1) The PZC may delegate to the Director authority to consider minor modification to approved hillside and foothill development permits. Minor modifications to Category III permits shall be limited to the following considerations:
(a) A reduction in development density which does not exceed 25 percent of the total units.
(b) A relocation of dwelling units, building pads, or building envelopes for some practical reason such as road alignment, topography, access, solar access, or stability in hillside areas.
(c) A change in the approved phasing plan or schedule.
(d) A modification to recreation area or open space design, but not including elimination or significant reduction.
(e) Minor change in proposed location of building envelope.
(2) Prior to approving a minor modification, the Director shall determine that the following are true:
(a) The requested modification was not specifically appealed during the public hearing process; and
(b) The requested modification will not cause adverse physical impacts on adjacent properties.
9. Application Requirements: All required information shall be prepared in conformance with the adopted Boise City Public Works Hillside Development Manual.