17.40.060 RETAINING WALLS

A.​ Retaining Wall Defined: Any structure designed to resist the lateral displacement of soil or other materials. Examples include, but are not limited to, block walls, rock walls, concrete walls and segmented walls. A retaining wall is not considered a fence. B.​ Regulations and Requirements: All retaining wall systems shall meet the requirements of this section. 1.​ All retaining walls that require a zoning clearance must be designed by an engineer licensed in the State of Utah. The design must be specific to the site and not a generic standard design. 2.​ If a retaining wall, less than four feet (4’) in height, is subjected to an external load (such as vehicular traffic, pedestrian traffic and parking), or permanent loads (such as protection systems against slope erosion, and adjacent structures), an engineered design shall be required. 3.​ Generally, zoning clearances for retaining walls are issued as separate permits and are not included in permits for new homes, remodels, additions, etc. If a retaining wall permit is combined with a permit for new homes, remodels, additions, etc., the application must include design plans, reports, and meet the requirements of this section. 4.​ Geologic Hazards. If construction of any retaining wall, occurs within sensitive land areas as outlined in Chapter 17.14 of this code, then all analyses required for the design of retaining walls or rock protected slopes shall follow the Sensitive Areas requirements, specifically in regards to limits of disturbance and the required geologic hazard and engineering geology reports. 5.​ Location, Height, Separation and Plantings: a.​ Location. The retaining wall will not be placed on land designated as a recorded easement, such as a utility or trail easement, unless the owner(s) of said easement agree(s) to allow the encroachment. Documentation of the agreement shall be provided to the City. b.​ To determine retaining wall height for zoning clearance, retaining walls shall be measured from the top of the exposed face to the top of footing. c.​ All retaining walls, four feet in height or taller, require a zoning clearance. d.​ Footings for retaining walls within the minimum setback cannot extend into the neighboring property e.​ Terracing of retaining walls is permitted where justified by topographic conditions. The total height of all terraces shall be considered for seismic and geotechnical investigation requirements unless each terrace is spaced at least three (3) times the retained height from other terraces. i.​ Landscaping, utilizing drip irrigation, to minimize erosion, and when possible, the use of drought resistant vegetation to minimize future watering needs is encouraged; or ii.​ The area may be utilized for accessory structures such as sports courts, gazebos, etc. that do not jeopardize the integrity of the retaining walls. f.​ Guards/railings will be required when a retaining wall is connected to or adjacent to a driveway or walkway. If a guard/railing is required, the combined height can exceed the height limitation set forth in Chapter 17.40 no more than the minimum height of the required guard/railing. g.​ Walls thirty inches (30”) or more in height may require guards/railings. If a guard/railing is optional, the height of the guard/railing will be added to the wall h.​ Clear view area. Placement of an individual retaining wall or a group of terraced retaining walls (including plantings) shall not obstruct within the triangular area formed by the street property lines and a line connecting them at points thirty feet (30') from the intersection of the property line. i.​ Joint ownership of walls. Occasionally, adjacent property owners will each benefit from a retaining wall placed on a shared property line. To receive approval for a joint wall all parties: i.​ Must agree in writing; ii.​ Must participate, either equally or proportionately, in the cost of the wall and installation; iii.​ Must have a written agreement, recorded against each affected lot, regarding ongoing repair and maintenance; iv.​ Must have an easement recorded with the County, if necessary. C.​ Submittals: The following documents and calculations prepared by a licensed engineer of the State of Utah shall be submitted with each retaining wall zoning clearance application: 1.​ Profile drawings if the retaining wall is longer than 25 linear feet, with the base elevation, exposed base elevation, and top of wall labeled at the ends of the wall and every 25 linear feet or change in grade; 2.​ Cross-sectional drawings including surface grades and structures located in front and behind the retaining wall a distance equivalent to three times the height of the retaining wall. If the retaining wall is supporting a slope, then the cross section shall include the entire slope plus surface grades and structures within a horizontal distance equivalent to one times the height of slope; 3.​ A site plan showing the location of the retaining walls with the base elevation, exposed base elevation and top of wall labeled at the ends of wall and every 25 lineal feet or change in grade; 4.​ A copy of the geotechnical report used by the design engineer. The geotechnical report shall include requirement of Part C.5, otherwise additional laboratory testing is required in Part C.5. A geotechnical investigation is not required for walls that retain less than 6 feet of backfill and are outside of sensitive land areas as defined in section 17.14; 5.​ Material strength parameters used in the design of the retaining wall, substantiated with laboratory testing of the materials as follows: a.​ Soils. This may include, but is not limited to, unit weights, direct shear tests, tri axial shear tests and unconfined compression tests. i.​ If laboratory testing was conducted from off-site but similar soils within a 2,000 foot radius of the proposed wall location, the results of the testing with similar soil classification testing needs to be submitted; ii.​ Minimum laboratory submittal requirements are the unit weight of retained soils, gradation for cohesion less soils, Atterberg limits for cohesive soils, and shear test data; iii.​ Soil classification testing shall be submitted for all direct shear or triaxial shear tests; iv.​ If a proctor is completed, classification testing shall be submitted with the proctor result; and, v.​ Laboratory testing should be completed in accordance with applicable American Society for Testing and Materials (ASTM) standards; b.​ Segmented (walls having a facing and lateral tieback system) block walls. The manufacturer's test data for the wall facing, soil reinforcement, and connection parameters shall be submitted in an appendix. 6.​ The design engineer shall indicate the design standard used and supply a printout of the input and output of the files in an appendix with factors of safety within the design standard used as follows: a.​ Design calculations ensuring stability against overturning, base sliding, excessive foundation settlement, bearing capacity, internal shear and global stability; b.​ Calculations shall include analysis under static and seismic loads, which shall be based on the peak ground acceleration (PGA) as determined from probabilistic analysis for the maximum credible earthquake (MCE), with spectral acceleration factored for site conditions in accordance with the current adopted building code; c.​ Mechanically Stabilized Earth (MSE) walls shall be designed in general accordance with current FHWA or AASHTO standards for design of Mechanically Stabilized Earth Walls and Reinforced Soil Slopes or the current National Concrete Masonry Association (NCMA) Design Manual for Segmental Retaining Walls; d.​ Rock walls shall be designed in general accordance with 2006 FHWA-CFL/TD-06-006 “Rockery Design and Construction Guidelines,” or current FHWA standard of care and; e.​ Concrete cantilever walls shall be designed in general accordance with specifications provided in current American Concrete Institute or American Society of Civil Engineers standards and specifications. 7.​ A global stability analysis with minimum factors of safety of at least 1.50 under static conditions and at least 1.10 under seismic loading conditions as follows: a.​ Factors of safety results shall be presented to the nearest hundredth; b.​ Seismic loads shall be based on the PGA as determined from probabilistic analysis for the maximum credible earthquake (MCE), with spectral acceleration factored for site conditions in accordance with the current IBC. Seismic loading is not required for walls that retain less than 6 ft backfill; c.​ The cross-sectional view of each analysis shall be included, and the printout of the input and output files placed in an appendix; and, d.​ The global stability analysis may be omitted for concrete cantilever retaining walls that extend to frost depth, that are less than nine feet in exposed height, absent of supporting structures within 30 feet of the top of the wall, and which have less than 10H:1V (H=horizontal: V=vertical) front and back slopes within 30 feet of the retaining structure. 8.​ A drainage design, including a free draining gravel layer wrapped in filter fabric located behind the retaining wall with drainpipe day-lighting to a proper outlet or weep holes placed through the base of the wall, however: a.​ A synthetic drainage composite may be used behind MSE walls if a materials specific shear testing is completed to determine friction properties between the backfill and synthetic drainage composite; b.​ A synthetic drainage composite is not allowed behind rock walls; c.​ A synthetic drainage composite may be used behind the stem of the concrete cantilever walls; d.​ If the engineering can substantiate proper filtering between the retained soils and the drain rock, then the filter fabric may be omitted, and; e.​ If the retaining wall is designed to withstand hydrostatic pressures or the retained soils or backfill is free-draining as substantiated through appropriate testing, then drainage material may be omitted from the design. 9.​ The design engineer’s acknowledgement that the site is suitable for the retaining wall. (Ord. 2026-5, 2026)