Ontario | ADUs and SB 9

Ontario, California ADUs and SB 9: ADU Classes, Sizes, Setbacks, Parking, Fees, Junior ADUs and Two-Unit Projects

An accessory dwelling unit, or ADU, is a second home on a lot that already has or will have a main home. A junior ADU is a unit of 500 square feet or less inside a house. Ontario's rules for both are Section 5.03.010 of the Development Code, which the City Council updated by urgency ordinance on December 16, 2025. Its rules for state SB 9 projects, two main homes on a house lot, are Section 5.03.403. This page sets out both sections and marks where each one differs from the state statute. The Ontario overview has the summary.

How the ADU Section Got Its Current Text

State ADU law changed on January 1, 2025 and again on January 1, 2026, and Ontario amended Section 5.03.010 each time. The City Council agenda of February 4, 2025 carried an urgency ordinance on ADUs under File No. PDCA24-004, and the agenda of April 1, 2025 listed the regular ordinance for adoption. On December 16, 2025 the Council took up File No. PDCA25-004. The minutes record that it "adopted an Urgency Ordinance" to amend Section 5.03.010 "to comply with recent changes to state law," with a motion that "carried by a unanimous vote of 5-0, to adopt Urgency Ordinance No. 3323." The posted Chapter 5.0, dated August 18, 2026, carries the amended text. The City's ADU handout is dated January 21, 2025 and is older than the code in three places noted below.

Two Classes of ADU

Section 5.03.010.D.3 sorts every ADU into one of two classes. Class 1 units are "Statutorily Regulated": they are the units that Government Code 66323 makes a city approve, and the City may add no design standard to them. Class 2 units are "Locally Regulated" and may be larger, in exchange for meeting the City standards in Subsection F.

Source: Ontario Development Code, Section 5.03.010.D.3 and F (Rev. 08.18.2026).

• Combining units. On a house lot, a converted ADU and a junior ADU "may be combined with" the limited detached ADU. On a multiple-family lot, converted ADUs may be combined with detached ones.
• Which zones. A Class 1 ADU "may be created on a lot in a residential or mixed-use zoning district." A Class 2 ADU may be created "on a lot that is zoned to allow single-family dwelling residential use or multiple-family dwelling residential use." A junior ADU "may only be created on a lot zoned for single-family residences."
• Density. A conforming ADU will not be "Deemed to exceed the allowable density for the lot" or counted under any program that limits residential growth.
• Existing problems on the lot. The City "will not deny an ADU or JADU application due to a nonconforming zoning condition, building code violation, or unpermitted structure on the lot that does not present a threat to the public health and safety and that is not affected by the construction of the ADU or JADU."
• An ADU outside the standards. Subsection I allows an ADU that does not meet the objective standards "subject to a Conditional Use Permit," a permit decided after a hearing.

Size, Setbacks and Height

• Size. A Class 2 ADU may have "850 SF of interior livable space for a studio or one-bedroom unit and 1,000 SF of interior livable space for a unit with 2 or more bedrooms." An attached ADU on a lot with an existing home "is further limited to 50 percent of the floor area of the existing primary dwelling."
• The 800 square foot guarantee. No use of the 50 percent limit, the front setback, the lot coverage limit or the open space rule "may require the ADU to have less than 800 SF of interior livable space."
• Side and rear setbacks. Class 2 ADUs "must conform to 4-FT side and rear setbacks." No setback is required for an ADU "constructed in the same location and to the same dimensions as an existing structure."
• Front setback. A Class 2 ADU must stay "30 FT from arterial street rights-of-way and 20 feet from all collector and local street rights-of-way," subject to the 800 square foot guarantee.
• Lot coverage. The ADU may not push total coverage past the zone limit: 30 percent in AR-2, 40 percent in RE-2 and RE-4, 50 percent in LDR-5 and 60 percent on a traditional house lot in the MDR zones and HDR-45, again subject to the 800 square foot guarantee.
• Stories. A Class 2 ADU may have one story. An attached ADU may have two.
• Near a listed historic property. A Class 2 ADU "on or within 600 feet of real property that is listed in the California Register of Historic Resources must be located so as to not be visible from any public right-of-way."

Source: Ontario Development Code, Section 5.03.010.E.2 (Rev. 08.18.2026). Height is measured "from existing legal grade or the level of the lowest floor, whichever is lower, to the peak of the structure." These limits match Gov. Code 66321.

Design, Windows and Landscaping for a Class 2 ADU

Subsection F adds design rules that apply to Class 2 ADUs only. They are written as measurable standards, so staff checks them with no hearing.

• Match the main home. "The materials and colors of the exterior walls, roof, and windows and doors must match the appearance and architectural design of those of the primary dwelling," and the roof slope must match the dominant slope of the main home.
• Room size. "The interior horizontal dimensions of an ADU must be at least 10 FT wide in every direction, with a minimum interior wall height of 7 FT."
• Privacy. "No window or door of the ADU may have a direct line of sight to an adjoining residential property." Each one is placed out of sight or screened with fencing, plants or privacy glass.
• Windows near a property line. Windows and doors "less than 30 FT from a property line that is not a public right-of-way line" must be clerestory, a high window "with the bottom of the glass at least 6 FT above the finished floor," or use frosted or obscure glass.
• Screening plants. A landscape plan is required. "At least one 15-gallon size screening shrubs shall be installed at every 5 linear feet of exterior ADU wall," or the owner may build "a 6-FT high decorative masonry block wall."
• Garage conversions. Where the garage door is removed, the wall gets "a minimum 3-FT wide foundation landscape planter for the full length of the wall."
• Lighting and entry. Exterior lights are down-lights, and the ADU has its own exterior entrance.

A separate rule covers a guesthouse, which is living space with no kitchen that may not be rented. Section 5.03.011 says "a Guesthouse shall not be constructed if an Accessory Dwelling Unit exists on the lot."

Parking

Class 1 ADUs and junior ADUs have no parking rule in the section. For a Class 2 ADU, "One off-street parking space is required for each ADU or bedroom, whichever is less," and the space "may be provided in setback areas or as tandem parking," one car behind another. No space is required when:

• the ADU "is located within one-half mile walking distance of public transit," which the section defines to include a bus stop;
• the ADU is in "an architecturally and historically significant historic district";
• the ADU "is part of the proposed or existing primary residence, or an accessory structure";
• on-street parking permits are required and are not offered to the ADU occupant; or
• "there is an established car share vehicle stop located within one block of the ADU."

Parking that is removed stays removed: "When a garage, carport, covered parking structure, or uncovered parking space is demolished in conjunction with the construction of an ADU or converted to an ADU, those off-street parking spaces are not required to be replaced." The general rule in Section 6.01.010 that a converted garage must be replaced makes an exception for an ADU.

Junior ADUs, Renting and Selling

• What a junior ADU is. A unit that "Is no more than 500 SF of interior livable space in size," is "contained entirely within an existing or proposed single-family structure," and has an efficiency kitchen with "A cooking facility with appliances" and a counter and cabinets "of a reasonable size in relation to the JADU." An attached garage counts as part of the house.
• Bathroom. A junior ADU may share a bathroom with the house. If it does, it needs an inside door to the main living area as well as its own outside entrance.
• Owner occupancy. "ADU's are not subject to an owner-occupancy requirement." For a junior ADU, an owner "must reside on the property, in either the primary dwelling or JADU," unless "The JADU has separate sanitation facilities" or the property is owned by a governmental agency, land trust or housing organization. This follows Government Code 66333 as amended effective January 1, 2026.
• Deed restriction. Before a junior ADU is occupied, a deed restriction is recorded with the County Recorder stating that it "may not be sold separately from the primary dwelling" and is limited to its approved size.
• Rental term. "No ADU or JADU may be rented for a term that is shorter than 30 days. This prohibition applies regardless of when the ADU or JADU was created."
• Sale. An ADU may be rented, and it may not be sold apart from the main home except as Government Code 66341 provides for homes built by a qualified nonprofit.
• Fire sprinklers. Sprinklers are required in an ADU only "if sprinklers are required in the primary residence."

The Permit, the Deadlines and the Fees

"If an ADU or JADU complies with each of the general requirements in Subsection E below, it is allowed with only a building permit." The City's ADU Permit Process page says the building permit application is submitted to the Building Department through the Citizen Portal Access website, and that plans may be reviewed by the Building, Planning, Engineering, Fire and Ontario Municipal Utilities Company departments.

• Completeness. The City says in writing whether the application is complete "within 15 business days after the city receives the application submittal," and must list what is missing. It "may not require the application to include an item that was not included in the original notice."
• Decision. "The City must approve or deny an application to create an ADU or JADU within 60 days from the date that the City receives a complete application. If the City has not approved or denied the complete application within 60 days, the application is deemed approved." When the ADU is filed with a new main home, the City may wait until it acts on that home.
• Denial and appeal. A denial comes with "a list of all the defective or deficient items and a description of how the application may be remedied." The applicant may appeal to the Planning Commission by writing to the City Clerk.
• Garage demolition. A demolition permit for a detached garage that the ADU replaces "is reviewed with the application for the ADU and issued at the same time."
• Impact fees. "No impact fee is required for a JADU or for an ADU that has less than 750 SF of interior livable space." A larger ADU pays in proportion: "the floor area of the ADU, divided by the floor area of the primary dwelling, times the typical fee amount charged for a new dwelling."
• School fees. A unit "with less than 500 SF of interior livable space" is "not subject to school fees."
• Utility connections. A junior ADU or converted ADU on a house lot needs no new connection and pays no connection fee or capacity charge, unless it is built with a new house. Other ADUs need "a new, separate utility connection" for City utilities, with a charge "proportionate to the burden created by the ADU."
• Older unpermitted units. The City may not deny a permit to legalize an ADU "constructed before January 1, 2020" for violating building standards or ADU rules, unless a correction is needed under the state substandard housing law.

The Planning Department fee schedule of August 22, 2026 has no line for an ADU. Building permit fees are set by the Building Department and were not read for this guide. The Preapproved ADUs page says "The City does not provide City Preapproved Plans for download," and that a plan from a pre-approved private vendor is plan checked "within 30 days" when used with no changes. The vendor list on the page reads "COMING SOON." The handout gives the Building Department number as (909) 395-2023 and the Planning Department number as (909) 395-2036.

Where the ADU Documents Differ

• Detached ADUs on apartment lots. The January 2025 handout says multifamily lots are eligible for "Two detached ADUs." The code now allows "up to 8 detached ADUs on a lot with an existing multiple-family dwelling." The code controls.
• The junior ADU kitchen. The handout defines an efficiency kitchen with counters "that total at least 15 square feet in area" and cabinets "that total at least 30 square feet of shelf space." The code and Government Code 66333 ask for a counter and cabinets "of reasonable size."
• The 750 square foot line. The code exempts an ADU with "less than 750 SF," and the handout says fees apply to a unit "750 square feet in area or larger." Government Code 66311.5 bars any impact fee on an ADU "that has 750 square feet of interior livable space or less." An ADU of exactly 750 square feet is exempt under the statute, and the statute controls.
• A cross-reference. Subsection F says it applies to Class 2 ADUs "approved under Subsection D.2." The classes are set out in Subsection D.3.
• Agriculture Overlay. Section 6.01.035 allows an "Accessory dwelling unit or guesthouse, not to exceed one per lot" in the AG Overlay and asks it to meet the setbacks of the main structure. State ADU law and Section 5.03.010 allow more than one unit and 4-foot setbacks on a lot with a house. Ask the City which it applies there.

SB 9 Two-Unit Projects

SB 9 is the state law that lets an owner build two main homes on a lot in a single-family zone with no hearing. Ontario calls this a "Single-Family Two-Unit Project" and regulates it in Section 5.03.403. The Planning Director approves or denies the application "ministerially," which means by checking it against written standards, and Table 2.02-1 sends appeals to the Planning Commission and the City Council. The statute is Government Code 65852.21, last amended effective June 30, 2026.

• Which lots. The lot must be legally subdivided and "in a single-family residential zoning district." The section adds that a site "likely qualifies" if its zoning "allows single-family uses as a primary use and multiple-family uses are prohibited." By the Land Use Matrix that describes AR-2, RE-2, RE-4 and LDR-5.
• Lots that are excluded. Farmland, wetlands, hazardous waste sites, flood hazard areas without the listed clearances, and conservation land. The lot may not be a historic property or sit in a historic district.
• Protected housing. The project may not demolish or alter income-restricted or rent-controlled housing or "Housing that has been occupied by a tenant in the last 3 years."
• Paperwork. The applicant obtains "a certificate of compliance with the Subdivision Map Act for the lot" and files it with the application. The City tells the applicant of anything missing within 30 days.
• Setbacks. The zone's setbacks apply, but they "shall yield to the degree necessary to avoid physically precluding the construction of up to two units on the lot or either of the two units from being at least 800 SF in floor area; but in no event may any structure be less than 4 FT from a side or rear property line."
• Walls and notice. The lot gets "6-FT high decorative masonry block walls" on interior side and rear lines. The owner gives written notice to adjoining owners "At least 30 business days before starting any construction."
• Ownership and use. The two homes may not be sold separately, condominiums are prohibited, no nonresidential use is allowed, and no home may be rented for less than 30 days. A deed restriction records these limits.
• ADUs with a two-unit project. "A lot that is not created by an Urban Lot Split may have a Two-Unit Project as provided by this Section, plus any ADU or JADU that shall be allowed pursuant to State law." On a lot made by an urban lot split, the limit is two units of any kind.

Sources: Ontario Development Code, Section 5.03.403 (Rev. 08.18.2026) and Section 2.02.015; Gov. Code 65852.21 as amended by Stats. 2026, Ch. 56 (SB 1426).

A city rule that is stricter than the statute allows is void to that extent, and the statute controls. The table shows seven places where the City text is narrower than the current statute. The City text also contains wording copied from the lot split section: its lot location rule speaks of "the lot to be split," and its deed restriction list ends with a statement that "the property is formed by an Urban Lot Split." One City rule is the opposite of the lot split section: "A Two-Unit Project shall be approved only if all nonconforming zoning conditions are corrected." Ask the Planning Department which size, height, garage and owner-occupancy rules it applies to a two-unit project today.

Limits of This Page

Section 5.03.010 and Section 5.03.403 were read from the Chapter 5.0 file named "Rev 08-18-2026." City Council agendas from January 7, 2025 to October 6, 2026 were read; the last ADU item is the urgency ordinance of December 16, 2025, and no agenda in that period lists an ordinance on two-unit projects. The text of Ordinance No. 3323, the Building Department fee schedule, the ADU Plan Submittal Requirements handout and the school district fee schedules were not read. The rest of the Ontario Municipal Code is hosted by an outside publisher whose site blocks scripted requests, and it was not read. Ask the Planning Department whether a newer ordinance is in force.

Where to Go Next

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

Frequently Asked Questions

Official sources (checked October 2026)