Hesperia | ADUs and SB 9

Hesperia, California ADUs and SB 9: Unit Sizes, the Septic Rule, the 2025 HCD Findings, Ordinance No. 2025-05 and Two-Unit Projects

An accessory dwelling unit (ADU) is a second, smaller home on the same lot as a house or apartment building, with its own kitchen and bathroom. A junior ADU (JADU) is a unit of 500 square feet or less inside a house. SB 9 is the 2021 state law that allows two main homes on a single-family lot. Hesperia has rewritten its ADU section several times, most recently in November 2025 after the state housing department found that the text did not comply with state law. The City has no section for SB 9. This page sets out the City text, the points where the statute decides, and the steps. The Hesperia overview has the summary.

Which Text Is in Force

The ADU rules are Section 16.12.360 of the Development Code. The Council staff report of October 21, 2025 gives the history: "On May 19, 2020, the City Council adopted Ordinance No. 2020-04 adopting development standards associated with ADUs. To date, the City Council has adopted four amendments to the existing ADU regulations." The history note of the section lists them: Ordinance Nos. 2021-01, 2022-13, 2024-13 of December 3, 2024 and 2025-01 of May 20, 2025.

A fifth amendment followed. The City Council introduced Ordinance No. 2025-05 on October 21, 2025, and the meeting record for November 4, 2025 lists it for second reading under Consent Ordinances, which the Council approved. The ordinance says it "shall take effect thirty (30) days from the date of adoption."

The Municode copy of the code does not show that amendment. Its Supplement History Table has rows for Ordinance Nos. 2025-04 and 2025-06, both dated November 4, 2025, and no row for 2025-05, and the history note of Section 16.12.360 ends at Ordinance No. 2025-01. This page reads the Municode text together with Exhibit A of Ordinance No. 2025-05 and says where the two differ. Ask the Planning Division for a current copy of the section before you design a project.

The ADU Rules (Section 16.12.360)

• Where. An ADU "may only be permitted on lots that are zoned for agricultural, single family, multi-family, or mixed uses and that contain an existing or proposed single-family or multi-family dwelling." ADUs "are exempt from the density limitations of the General Plan." The use table lists an ADU as an accessory use in R1, R3, RR, A1 and A2.
• Size. "A detached accessory unit shall not exceed one thousand two hundred (1,200) square feet of livable floor area (excludes garage and any accessory structure) on any parcel." An attached ADU "may be up to fifty (50) percent of the area of the principal unit, up to a maximum of one thousand (1,000) square feet." "No accessory dwelling unit shall be less than one hundred and fifty (150) square feet in area."
• The 800-square-foot floor. "No provisions within this Section, including lot coverage or legal nonconformity, shall preclude either an attached or detached eight hundred (800) square-foot accessory dwelling unit with four-foot side yard and rear yard setbacks."
• Setbacks. A setback is the open distance a building must keep from a lot line. "For new attached or detached accessory dwelling units, a minimum four-foot side yard and four-foot rear yard setback is allowed. The front yard and street side yard standards for the primary unit shall apply." No setback is required for a conversion of existing living area or of an existing accessory structure.
• Height. A detached ADU "may not exceed sixteen (16) feet in height," or 18 feet within one-half mile walking distance of a major transit stop or a high-quality transit corridor, with "two additional feet in height to accommodate a roof pitch" that matches the house. An attached ADU "may not exceed twenty-five (25) feet in height or exceed two stories."
• Entrance and look. "Independent access to an attached accessory dwelling unit is required and shall not be located on the same wall plane elevation as the access to the primary dwelling." The ADU "shall be architecturally compatible with the design of the primary unit and shall match with the same colors and materials of the primary unit."
• Parking. The section sets no parking space for an ADU. When a garage, carport or covered parking structure is demolished or converted for an ADU, "those off-street parking spaces do not need to be replaced."
• Other buildings. The ADU's area "is in addition to and shall not be considered as part of the allowable accessory building area" of Section 16.20.390, which is 1,000 square feet or up to 7.5 percent of the net lot area.
• Recreational vehicles. "A recreational vehicle, does not qualify for use as an accessory dwelling unit." A manufactured home does qualify, and the City's application asks for a unit "no more than 10 years old."
• Rentals and sale. The ADU "shall not be used for a rental term of less than thirty (30) consecutive days." It may not be sold apart from the house, with one exception for homes built by a qualified nonprofit corporation for low-income buyers.
• Animals next door. "The construction of an accessory dwelling unit shall not be considered when calculating minimum distance requirements for animal uses on the subject lot or on adjacent lots."

Lots on Septic Systems

Many Hesperia house lots have a septic system, a private tank and drain field that treats wastewater on the lot, in place of a sewer connection. The ADU section has a rule for them: "In compliance with the State of California Lahontan Regional Water Quality Control Board, lots that are not connected to sewer facilities shall be a minimum of one gross acre in size or install an approved Supplemental Treatment Septic System." The Housing Element repeats it: "Lots not connected to sewer shall be a minimum of 1 acre in size."

A junior ADU follows a different rule. For water, sewer and power service, "a junior accessory dwelling unit shall not be considered a separate or new dwelling unit," and a lot with no sewer "shall meet the Lahontan Regional Water Quality Control Board regulations pertaining to minimum septic tank capacity."

State law has two rules on the same subject. Government Code 66314 says a city's ADU standards "shall not include requirements on minimum lot size," and it also lets an ordinance require "Approval by the local health officer where a private sewage disposal system is being used." Government Code 66323 lets a city require, for an ADU on an onsite wastewater system, "a percolation test completed within the last five years." The state housing department did not list the one-acre rule among its 2025 findings. An owner of a septic lot under one acre should ask the Planning and Building divisions, in writing, which of these rules they apply. The sewer, septic and flood page covers when a sewer connection is required.

Junior ADUs

• Where. A junior ADU "may only be permitted on lots that are zoned for agricultural or single family and that contain an existing or proposed single-family dwelling."
• Size and place. It "shall not exceed five hundred (500) square feet in size and shall be contained entirely within a single family residence." The 2025 text adds that "enclosed uses within the residence, such as attached garages, are considered a part of the proposed or existing single-family residence."
• Kitchen and bathroom. It needs "an efficiency kitchen that includes a cooking facility with appliances, a food preparation counter, and storage cabinets." It "may have a bathroom or share with the proposed or existing single family residence."
• Entrance. "A separate entrance from the main entrance" of the house.
• Garage parking. A junior ADU "shall not convert the required parking for the primary residential structure located within an attached garage without the concurrent replacement of the existing required parking within an enclosed garage elsewhere on the property."
• Deed restriction. A recorded restriction bars separate sale, limits the size, bars rentals of less than 30 days and requires "owner occupancy of one of the units on-site," unless the owner is "a governmental agency, land trust, or housing organization."

The 2025 HCD Findings and the City's Answer

The California Department of Housing and Community Development (HCD) reviews city ADU ordinances under Government Code 66326. Its letter of June 19, 2025 reviewed Ordinance No. 2024-13 and said "HCD finds that the Ordinance fails to comply with State ADU Laws in the manner noted below." It listed six points. The City answered with Ordinance No. 2025-05.

• Changed: the decision. The words "act on" became "approve or deny" within 60 days.
• Changed: apartment lots. The old limit of two detached ADUs was replaced. "Within an existing multi-family development, up to a maximum of eight (8) detached ADUs may be constructed provided that the total number of ADUs does not exceed the number of existing units on the lot." "Within a proposed multi-family development, up to a maximum of two (2) detached ADUs may be constructed." Inside an existing apartment building, ADUs may also be made from space that is not lived in, at least one and up to 25 percent of the existing homes.
• Changed: building codes. Each ADU "shall conform to all applicable provisions of the California Residential Code and the California Building Code."
• Added: apartment parking. "An ADU shall not convert the required parking for an existing or proposed multi-family dwelling within an enclosed garage or carport without the concurrent replacement of the existing required parking elsewhere on the property," unless state ADU law provides otherwise.
• Refused: three units on a house lot. HCD wrote that state law "permits a homeowner to create one converted ADU; one detached, new construction ADU; and one JADU." The staff report answers "The City has elected not to amend the Ordinance in response to comment No. 2," and says the City "respectfully disagree with HCD's Finding." The text still allows "one accessory dwelling, and one junior accessory dwelling unit."
• Refused: size limits. The City kept its size limits for ADUs that HCD said state law exempts, and added a new subsection (D)(13): "Notwithstanding any other provision in this Section 16.12.360, the City shall ministerially approve an application for a JADU and/or one or more ADUs if the proposed unit meets the requirements of Government Code Sections 66323." Ministerially means by applying fixed written rules, with no judgment call.

The statute changed after the City wrote its answer. The City's argument relied on the words "any of the following" in Government Code 66323. As amended effective January 1, 2026, that section requires approval of an application "to create any of the following units, or any combination of the following units." Government Code 66316 says a local ordinance that "fails to meet the requirements of this article" is "null and void" to that extent and the state standards apply. Read with subsection (D)(13), the statute means a Hesperia house lot may have a converted ADU, a junior ADU and one detached new ADU, where the detached unit may be held to 800 square feet and the state height limits.

Sources: Hesperia Municipal Code 16.12.360 (Supplement 24 Update 2); Ordinance No. 2025-05, Exhibit A; ADU application packet; Gov. Code 66323, 66317, 66333 and 66314.

Applying for an ADU

• The review. "The review procedure shall be administrative review without notice (ministerial)." Staff decide, and neighbors receive no notice.
• What to file. The City's application packet asks for a site plan to scale, a floor plan that shows the use of each room, elevations of all sides and a copy of the grant deed, two copies each of the plans. The form asks for the "Method of sewage Disposal": sewer connection, septic system or onsite wastewater treatment system.
• The planning fee. The fee chart lists "Accessory Dwelling Units/ JR Accessory Dwelling Unit" at $312 and says "TOTAL FEES ARE SUBJECT TO A 10% AUTOMATION FEE." The fee schedule also lists $165 for review of a site design water quality management plan for an ADU.
• The time limit. Sixty days from a completed application. Government Code 66317 adds a written notice of completeness "not later than 15 business days" after filing, and says that if the City has not decided in 60 days "the application shall be deemed approved." A denial must come with "a full set of comments" on how to fix the application.
• With a new house. Where the ADU is filed with a permit for a new house, the City may wait to act on the ADU until it acts on the house.
• Building permit. The ADU is built to "minimum standards for single-family residential uses on individual lots as specified in Section 16.20.160, unless otherwise specified." That section covers siding, roofing and eaves of at least 12 inches. Its minimum house sizes "do not apply" to "second dwelling units constructed on lots where a primary dwelling unit is constructed."
• Impact fees. Government Code 66311.5 bars any impact fee on an ADU "that has 750 square feet of interior livable space or less," and requires fees on a larger one to be "charged proportionately in relation to the square footage of the primary dwelling unit." The City's fee schedule has no separate impact fee line for ADUs. See the permits and fees page.
• Renting. The City's Rental Housing Business License and Inspection Program says "Registration is required for all rental properties under Hesperia Municipal Code Chapter 5.72." Its list of exemptions includes "Junior ADUs within owner-occupied homes."

ADUs are a small share of new homes in Hesperia. The staff report on the 2025 annual report says "the City issued building permits for 505 single-family homes and 23 accessory dwelling units (ADUs), resulting in a total of 528 residential units permitted during the year." The Housing Element, adopted in 2023, counted 14 second units built or in development since January 1, 2014.

SB 9 Two-Unit Projects

A search of the Hesperia Development Code, as published through December 5, 2025, found no section on SB 9 and no mention of Government Code 65852.21. The City's forms page lists no SB 9 application. The R1 use table lists no duplex. For an R1 owner, the statute is the rule. Government Code 65852.21, as amended effective June 30, 2026, says a proposal "containing no more than two residential units within a single-family residential zone shall be considered ministerially, without discretionary review or a hearing."

Source: Gov. Code 65852.21, as amended effective June 30, 2026.

• Sites excluded. The project may not require demolishing or altering housing with rent limits, or "Housing that has been occupied by a tenant in the last three years." Historic landmarks and districts are excluded.
• City standards. A city may apply objective standards, ones that "involve no personal or subjective judgment by a public official," as long as they apply uniformly in the zone and leave room for two homes of 800 square feet.
• Two Hesperia standards to check. Section 16.20.160 requires "a fully enclosed two-car garage" for residential structures and a minimum house size of 1,000 square feet. The statute allows "Offstreet parking of up to one space per unit." On parking the statute sets the upper limit for an SB 9 home. Ask the Planning Division how it applies the house size rule to a second home.
• Grounds to deny. Only a written finding by the building official of "a specific, adverse impact" on "public health and safety" that cannot be mitigated.
• ADUs with SB 9. A city "shall not be required to permit an accessory dwelling unit or a junior accessory dwelling unit on parcels that use both" the two-unit rule and an urban lot split. The lot size and subdivisions page covers the split.
• Which designations. R1 is Hesperia's Single-Family Residence designation. The City has not published a list of the designations it treats as single-family zones for SB 9; ask before you rely on the law in RR, A1 or a Specific Plan zone.

Where the City's Own Documents Differ

• Sixty or 120 days. The City's application packet says "The City shall act on the application to create an ADU or a Junior ADU within 120 days." The code says sixty days, and so does the statute. Sixty days controls.
• Adoption dates. Ordinance No. 2025-05 recites that Ordinance No. 2024-13 was adopted "on November 19, 2024" and Ordinance No. 2025-01 "on May 6, 2025." The code's history note and the Supplement History Table give December 3, 2024 and May 20, 2025. The Council records show the earlier dates were first readings and the later dates second readings.
• The title of the ordinance. The title of Ordinance No. 2025-05 calls it an ordinance "RECOMMENDING THAT THE CITY COUNCIL ADOPT A DEVELOPMENT CODE AMENDMENT." Its operative section says "the City Council hereby adopts Development Code Amendment DCA25-00003."
• Housing Element summary. The Housing Element says "On properties zoned for multi-family, up to 1 unit may be converted from existing non-habitable space." The code allows at least one and up to 25 percent of the existing homes.

Where to Go Next

Related on VanPlex: the Hesperia overview, the California ADU law page and the SB 9 page.

Frequently Asked Questions

Official sources (checked October 2026)