San Bernardino | Hillside, fire and flood zones

San Bernardino, California Hillside, Fire and Flood Zones: Slope Density, Foothill Fire Standards, Flood Plain Permits and What They Mean for ADUs and SB 9

The northern part of the City of San Bernardino is foothill land, and three overlay zones in the Development Code change what can be built on part of the city. An overlay zone is a second set of rules that applies in addition to the base zone. The Hillside Management Overlay sets density by slope. The Foothill Fire Zones Overlay adds street, water, spacing and material rules. The Flood Plain Overlay covers the flood hazard areas on the federal flood maps. This page covers each one and what it does to a house, an ADU or a lot split. The San Bernardino overview has the summary.

Hillside Management Overlay: Density by Slope

Source: San Bernardino Development Code, Sections 19.17.060(1) and 19.17.070(1) (pages dated Oct. 2019).

Chapter 19.17 states its purpose as "to provide for low-density residential development in the City's hillside areas." Slope is the rise of the land divided by its run, as a percent. The overlay is "the approximate location of the hillside areas along the foothills in the northern area of the City," and the foothill area is "that area of 15% or greater slope as shown on the General Plan Land Use Plan map."

• The overlay number replaces the zone number. "Notwithstanding the density allowed by the underlying land use district," the maximum density "shall not exceed the units per acre for each of the average percent slope ranges."
• It is a maximum. "The computation of the maximum number of lots is intended solely to set up an absolute maximum. A lesser number of units may prove to be the maximum permitted."
• Density transfer. A project may move homes from a steeper slope category to a gentler one, and "the allowable density of the lower slope category may be increased by 50%." The code's example moves homes from land over 30 percent to land of 0 to 15 percent, where density rises "from two units per acre to three units per acre." The project total may not exceed what it would have been with no transfer.
• Flatter land at the base. "Areas of 15% natural slope or less along the external border of the zone at the base of the hillsides, as determined by the preparation of a slope map by a licensed civil engineer, may be excluded" and go back to the base zone's density.
• Lot size and setbacks. "No absolute minimum parcel size, widths and depths are specified," and setbacks "shall be determined based upon the precise development plan and environmental studies."
• Attached homes. Table 04.02 allows attached dwelling units in RE, RL and RS only inside this overlay, at an average of six in a building.

Hillside Permits and Reports

The overlay changes who decides. "A Conditional Use Permit shall be required for all tentative tract and parcel maps and non-residential uses," and for "all applicable uses and structures permitted in this overlay zone except in-fill single family homes on existing lots of record which will require a Development Permit." A Conditional Use Permit is decided by the Planning Commission after a public hearing. The code adds that "the Director shall review and act upon all Development Permits for single family residences on existing lots."

• Application contents. A topographic map at a scale of at least one inch to 100 feet, a site plan, a preliminary grading plan, "Colored maps of existing and final slope" in the four slope categories, sections or elevations, a soils engineering report, a hydrology report and a preliminary landscaping plan.
• Trees. A tree map must show trees "with a trunk diameter of six inches or greater or having a vertical height from ground level to tree-top level of 25 feet or greater," and "No such trees shall be removed without prior written approval of the Commission."
• How the Commission judges it. "In general, the project shall be designed to fit the existing topography; the site shall not be graded to accommodate the project." The project should avoid "significant intrusion(s) into the view from adjoining up-slope residences."
• Waivers. The Director may drop a report where "Recently completed and satisfactory reports covering the same subject matter of the same site" exist.
• Life of the permit. Under Chapter 19.36, construction must start "Within two years of Conditional Use Permit or Minor Use Permit approval."
• Fees. The Planning Division fee schedule lists a Development Permit with Director review at $2,043.60. Its Conditional Use Permit lines are named for alcohol licenses, billboards and "Standard (Commercial and Industrial)" at $5,777.20, so ask which line the City uses for a hillside housing permit.

Hillside Building Rules

• Height of an infill house. For a house of more than one story on an existing lot, where the lot sits between 8 and 20 feet below the next lot uphill, "The maximum height of a proposed structure shall not exceed the midpoint of the structure on the immediately uphill lot." Where the uphill lot is empty, the limit is "a point eight feet above the average ground level of the uphill lot." The rule does not "prohibit a single story residence."
• Ridgelines. "The highest point of any structure shall not be located above the ridgeline." The code defines a ridgeline as "a long, narrow, conspicuous elevation which is visible north of Highland Avenue" from a freeway or a major, secondary or collector street.
• Graded slopes. "Slopes created by grading of the site shall not exceed 50 percent or 2:1, without a soils report and stabilization study," and may not exceed "30 feet in height between terraces or benches."
• Paved area. "Maximum coverage of a parcel by impervious surfaces shall not exceed 40% of the gross land area." An impervious surface is one that water cannot soak through, such as a roof or pavement.
• Earthquake faults. "No structure for human occupancy shall be permitted within 50 feet of an active or potentially active fault trace." Buyers must be told of the seismic hazard at the purchase agreement and at the close of escrow.
• Retaining walls. One wall per lot of up to eight feet on the upslope side and one of up to 42 inches on the downslope side. "Exposed retaining walls facing roadways shall be no greater than 5 feet in height."
• Plants. "If removal is required, reestablishment of a compatible plant material will be required at a ratio of at least 2:1."
• Colors. Exterior finishes "should blend in with the natural surroundings by using earth tone colors and avoiding reflective materials or finishes."
• Streets. Hillside collector and arterial streets may not exceed an 8 percent grade and residential streets 15 percent, and each tentative map needs "at least two different standard routes for ingress and egress."

Foothill Fire Zones Overlay

Chapter 19.15 "identifies three foothill fire zones that have different degrees of hazard based on slope, type of fuel present and natural barriers. The foothill fire zones are: A-Extreme Hazard, B-High Hazard, and C-Moderate Hazard." Zones A and B "shall be determined by the slope analysis, submitted with the project application," and "A reference map specifying identified fire zones within the City is on file with the Department." Each standard ends with the letters of the zones it applies to.

Source: San Bernardino Development Code, Section 19.15.040 (pages dated Oct. 2019).

• Every new structure. "All new structures requiring permits, including accessory structures, guest housing or second units shall conform to all applicable fire zone standards." For the ADUs a city must approve, Government Code 66323 says a city "shall not impose any objective development or design standard that is not authorized by this section." Spacing of 30 or 60 feet between structures is not in that section, so ask the City in writing which fire zone standards it applies to an ADU.
• Where a building may sit. "Structures shall be located only where the upgraded slope is 50% or less." Next to a slope "greater than 50%" and "greater than 30 feet in height," the building pad needs "a minimum pad setback of 30 feet from the edge of the slope."
• Lot lines. "All proposed property lines shall be placed at the top of slopes."
• Access to the wildland side. A subdivision provides either a perimeter street along the wildland side or "a fuel-modified area, a minimum of 150 feet in depth from the rear of the structure," reached by 12-foot access ways no more than 350 feet apart.
• Fuel modification. This is a strip where "flammable native vegetation has been removed or modified, and partially or totally replaced with drought tolerant fire-resistive plants." The plan includes "a 'wet zone' of a minimum depth of 50 feet of irrigated landscaping" and thinning zones of 100 feet.
• Building materials. Materials and methods follow Section 15.10 of the Municipal Code. The City Council agenda of August 5, 2026 listed the adoption of Ordinance No. MC-1666, which would "approve use of the 2025 California Building Code and other minor changes to Chapter 15."
• Disclosure. "All future transfers of property shall disclose to the purchaser at the time of purchase agreement and the close of escrow the high fire hazard designation applicable to the property."
• Maintenance. Fuel modification zones "shall be maintained, when required, through homeowner associations, assessment districts or other means."

The hillside chapter links the two overlays: "All developments in this overlay zone shall comply with the standards of the FF (Foothill Fire Zones) Overlay Zone."

Dividing Land in the Foothills

• Two access routes. Section 19.30.200 requires two standard routes for every tentative map, each a dedicated road with at least 24 feet of paving. In a Foothill Fire Zone the Planning Commission may accept one standard and one non-standard route, and "In no event may a tentative map be approved within a Foothill Fire Zone unless 2 access routes are provided, of which 1 shall be standard."
• Conditional Use Permit. A parcel map in the hillside overlay needs one, as described above.
• SB 9 lot splits and two-unit projects. The City's SB 9 sections exclude a lot "Within a very high fire hazard severity zone, unless the site complies with all fire-hazard mitigation measures required by existing building standards." They then list City measures: "direct access to a public right of way with a paved street with a width of at least 40 feet," with "at least two independent points of access," sprinklers in all enclosed structures, every side of every home "within a 150-foot hose-pull distance" of the street or a hydrant, and "a water reservoir of at least 5,000 gallons per dwelling" where the lot has no swimming pool. For a lot split the applicant must first "obtain a certificate of compliance with all applicable fire-hazard mitigation measures."
• What the statute says. Government Code 65852.21 takes its site limits from another statute "as that section read on September 16, 2021." It also bars standards "that do not apply uniformly to development within the underlying zone," and the City's 40-foot street and 5,000 gallon reservoir rules apply only to SB 9 projects. Ask the Planning Division how it applies them.
• Small-lot maps. Government Code 66499.41, the SB 684 and SB 1123 statute, leaves out a site "Within a very high fire hazard severity zone, as determined by the Department of Forestry and Fire Protection."
• Specific plans. The City's Specific Plans page posts plans named Arrowhead Springs, Spring Trails and University Hills, among others. This guide did not read them.

The fire zones in Chapter 19.15 are the City's own, set by slope. The very high fire hazard severity zone named in the SB 9 sections is a state designation. This guide did not read the state or City fire hazard maps, so it does not say where either line falls. The City's ADU page says only that "the city does have high wind areas, high seismic areas and high fire severity areas."

Flood Plain Overlay

Chapter 19.16 applies "to all areas of special flood hazards, areas of flood-related erosion hazards and areas of mud slide (i.e. mud flow) hazards within the jurisdiction of the City." Those areas are the ones identified by the Federal Emergency Management Agency "in the Flood Insurance Study dated March, 1996, and accompanying Flood Insurance Rate Maps, and all subsequent amendments and/or revisions." The base flood is "The flood having a 1% chance of being equaled or exceeded in any given year," which the code also calls the 100-year flood.

• Permit. "A Flood Control Development Permit shall be obtained before construction or development begins within any area of special flood hazards." The application goes to the City Engineer and shows the "Proposed elevation in relation to mean sea level, of the lowest floor (including basement) of all structures."
• Floor elevation. "New construction and substantial improvement of structure shall have the lowest floor, including basement, elevated to or above the base flood elevation." On completion the elevation "shall be certified by a registered professional engineer."
• Shallow flooding zones. In Zone AH, AO or VO the lowest floor must be "elevated above the highest adjacent grade at least as high as the depth number specified in feet on the FIRM, or at least 2 feet if no depth number is specified." FIRM stands for Flood Insurance Rate Map.
• Enclosed areas below the floor. They need "a minimum of two openings having a total net area of not less than one square inch for every square foot of enclosed area subject to flooding," with the bottom of each opening "no higher than one foot above grade."
• Substantial improvement. "Any repair, reconstruction, or improvement of a structure, the cost of which equals or exceeds 50% of the market value of the structure." An addition or remodel of that size must meet the rules for new construction.
• Manufactured homes. They must "Be elevated so that the lowest floor is at or above the base flood elevation" and be anchored.
• Subdivisions. Map applications must "Identify the flood hazards area and the elevation of the base flood," and "All Final Maps shall provide the elevation of proposed structure(s) and pads."
• Floodways. A floodway is the channel and adjacent land that must stay open to carry the base flood. The code prohibits "encroachments, including fill, new construction, substantial improvements, and other development unless certification by a registered professional engineer or architect is provided demonstrating that encroachments shall not result in any increase in flood levels."
• Mud slide areas. In areas with mud slide hazards, "A site investigation and further review shall be made by persons qualified in geology and soils engineering."
• Variances. The Planning Commission hears appeals and flood variances. "Generally, variances may be issued for new construction and substantial improvements to be erected on a lot 1/2 acre or less in size contiguous to and surrounded by lots with existing structures constructed below the base flood level."
• Penalty. Violations "shall constitute a misdemeanor."
• No guarantee. "Larger floods can and will occur on rare occasions," and the chapter "shall not create liability on the part of the City."

Flood control channels have their own zone. Chapter 19.10 says the purpose of the PFC (Public Flood Control) zone "is to provide for the continuation, maintenance, and expansion of public flood control facilities." Chapter 19.06 describes a third Central City South zone, CCS-3, that "is intended to provide for the flood control channel." The purpose of each zone is flood control alone. The City's SB 9 sections also exclude a lot in a 100-year flood hazard area unless it has a federal map revision or meets federal floodplain criteria, and a lot in a regulatory floodway "unless all development on the site has received a no-rise certification."

Where the Code Is Unclear or Disagrees With Itself

• Infill houses in the hillside overlay. Section 19.17.040 says uses "shall be the same as those for the underlying district," Section 19.17.050 asks for a Development Permit for an infill house, and Section 19.17.080 says an owner "shall submit a Conditional Use Permit Application" to start a project on any parcel. Section 19.17.080 itself adds that the Director acts on Development Permits for single family residences on existing lots, so this guide reads an infill house as needing the Development Permit alone. Confirm it with the Planning Division.
• A repeated line. Section 19.16.070 prints the same requirement, on grading that must "not aggravate the existing hazard," as both item B and item C.
• A cross-reference in the flood chapter. The flood chapter refers map applicants to "Section 19.48 and 19.50 (content and form)." The content and form of tentative maps is in Section 19.66.110.
• Old code names. The mud slide section of the flood chapter cites "Chapter 70 of the Uniform Building Code," and Chapter 19.04 sets room sizes "Subject to adopted UBC Standards." The Council agenda of August 5, 2026 lists the 2025 California Building Code for adoption, so ask the Building and Safety Division which code edition applies.

Limits of This Page

The three overlay chapters are the City's posted copies with pages dated Oct. 2019. Planning Commission and City Council agendas from January 2025 to October 7, 2026 list no ordinance amending them. This guide did not read the Official Zoning Map, the General Plan map that shows the 15 percent slope line, the fire zone reference map on file with the Department, the state fire hazard severity maps, the federal Flood Insurance Rate Maps, Title 15 of the Municipal Code, or the foothill specific plans. It cannot say whether a given lot is inside an overlay. Ask the Planning Division and the Land Development Division for the overlays on your lot before buying. Land outside the city limits follows San Bernardino County's rules.

Where to Go Next

Related on VanPlex: the San Bernardino overview, the California property tax and insurance page and the California lot eligibility page.

Frequently Asked Questions

Official sources (checked October 2026)