Rialto | ADUs and SB 9

Rialto, California ADUs and SB 9: The 2020 ADU Rules, State Law Overrides, Pre-Selected Plans 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. Rialto's ADU rules date from 2020, and state ADU law has changed several times since, so on several points the statute now decides what a Rialto owner may build. This page sets out the City's text, where the state rule controls, the City's pre-selected ADU plans and the City's SB 9 chapter. The Rialto overview has the summary.

Rialto's ADU Section

Section 18.10.070 was added by Ordinance No. 1641 on July 14, 2020, and Supplement 39 shows no later amendment. It still cites "Government Code Section 65852.2 et seq." The state ADU rules now sit in Government Code Section 66314 and the sections that follow it; SB 477 added several of them, such as Sections 66315 and 66322, in 2024. The section makes ADUs "a permitted use on all lots in single-family and multi-family residential zones." An ADU may be attached, inside the house or an attached garage, or detached, and must be on the same lot as the house.

• Approval. An application goes to the Community Development Department and "must be ministerially approved or denied within sixty days, without a hearing," once complete. Ministerial means staff check fixed written rules and have no discretion to say no for other reasons. Government Code 66317 adds that a complete application not acted on in 60 days "shall be deemed approved."
• Size. No more than 50 percent of the house or 850 square feet, "whichever is more," or 1,000 square feet with more than one bedroom, and never more than 1,200 square feet. A converted building may grow by up to 150 square feet for entry and exit.
• Setbacks and coverage. Four feet from side and rear lines. If lot coverage would block an ADU of at least 800 square feet, an ADU of up to 800 square feet is still allowed.
• Location and entry. An ADU must sit behind or beside the house unless the Director agrees only a front site works. An attached ADU needs its own outside door, "not located on the front elevation." No new driveway from the street is allowed.
• Garage conversions. The garage door must be removed and replaced with windows, a door or other treatment that matches the house. Lost garage spaces need not be replaced.
• Rentals and sale. Rentals must be longer than thirty days. The ADU "shall not be sold separately from the primary unit."
• Utilities. A new ADU, other than a conversion, "shall be metered separately from the primary unit for gas, electricity, and water/sewer services."

Where State ADU Law Now Controls

A city ADU rule that is stricter than state law is void to that extent, because state law sets the minimum a city must allow. Government Code 66322 applies "whether or not the local agency has adopted an ordinance." The table compares Rialto's 2020 text with the statutes in force in 2026.

Sources: Rialto Municipal Code Sec. 18.10.070 (Supplement 39); Gov. Code 66323, 66321, 66333, 66311.5 and 66322.

• Number of ADUs. Section 18.10.070 says "No more than one accessory dwelling unit and one junior accessory dwelling unit are allowed on any lot with an existing or proposed single-family residence." Government Code 66323(a) requires a city to approve "any combination" of a converted ADU and JADU, and "One detached, new construction, accessory dwelling unit" of up to 800 square feet with four-foot setbacks.
• Apartment lots. The code allows one attached ADU "for every four dwelling units" and two detached ADUs. The statute requires at least one ADU and up to 25 percent of the existing homes in unused space, and "not more than eight detached accessory dwelling units" that do not outnumber the existing homes.
• Height. The code's limit of "sixteen feet or one story, whichever is less" is lower than Government Code 66321(b)(4) for an attached ADU (25 feet or the zone limit) and for a detached ADU near a major transit stop (18 feet). Public Resources Code 21064.3 counts "An existing rail or bus rapid transit station" as a major transit stop, and the Housing Element places "the Rialto Metrolink Station" next to its Central Area housing sites.
• Design. Section 18.10.070 requires an ADU "architecturally compatible with the primary structure and structures in the immediate neighborhood." Government Code 66314(b)(1) allows "objective standards," meaning standards that involve no personal judgment, so a design rule must be measurable to apply.
• Junior ADU owner rule. The code requires owner occupancy "In the case of a junior accessory dwelling unit." Government Code 66333(b) allows that rule only if the JADU shares sanitation with the house: "Owner-occupancy shall not be required if the junior accessory dwelling unit has separate sanitation facilities."
• Fees. The code bars impact fees on an ADU "under seven hundred fifty square feet." Government Code 66311.5(c) bars them for an ADU of "750 square feet of interior livable space or less," so an ADU of exactly 750 square feet pays none.

The Pre-Selected ADU Plans and the Permit Steps

The City's Accessory Dwelling Units page offers two methods: the "Pre-Selected ADU Plans Program" or a custom design by an architect or designer. The program lists eleven plans "from other municipalities," from ADU1 (499 square feet, one bedroom, Santa Ana) to ADU11 (1,200 square feet, three bedrooms, Riverside), with others from Menifee, Chino and Temecula. "The designer of the plans is Design Path Studios," and owners contact that firm for approval to use them. The Housing Element calls them "11 pre-approved ADU plans" and says the program streamlines review.

• Step 1, Planning. Email [email protected] a site and utility plan, the plans, a building permit application, a hold harmless agreement and the checklist. "The City of Rialto will require a new address for each unit on a property," and Planning contacts the owner "within five business days." The address letter has "Currently no fee."
• Step 2, Building and Safety. Submit the address letter, plans, Title 24 energy forms, a solar plan and fire sprinkler plans if needed to [email protected].
• Fees. "School fee letter is required regardless of square footage," and the school district "Typically" charges ADUs of 500 square feet or more. The page lists three school districts: Colton Joint Unified, Fontana Unified and Rialto Unified. The page says "All new ADU's constructed at the same time as a new dwelling must pay DIF fees," meaning development impact fees.

The Housing Element (Program 2D) says the City "adopted an Accessory Dwelling Unit Ordinance in 2020" and "will support and accommodate the construction of at least 128 ADUs." It also says "ADUs go directly to the Building Division for permits." Economic Development Committee agendas for August 28, September 18 and October 30, 2025 listed an "Amendment to the Accessory Dwelling Unit (ADU) Ordinance" with a revised draft. No adopted amendment appears in the City Council records read through October 2026.

SB 9 Two-Unit Projects (Chapter 18.113)

Chapter 18.113, adopted by Ordinance No. 1665 on February 8, 2022, defines a "two-unit project" as "the development of two primary dwelling units, or if there is already a primary dwelling unit on the lot, the development of a second primary dwelling unit." It applies in "a zone where the only residential use that is allowed as a primary use is a single residential dwelling on a lot," which covers the R-1 zones. The applicant must first obtain "a certificate of compliance with the Subdivision Map Act," a document showing the lot was legally created. The City reports any missing items within thirty days.

Source: Rialto Municipal Code Sec. 18.113.050 (Supplement 39).

• Approval. The Community Development Director approves or denies "ministerially," and the approval takes effect only after the deed restriction (a recorded limit on how the property may be used) and easements are recorded. The decision "is final and non-appealable."
• Sites excluded. Prime farmland, wetlands, hazardous waste sites, protected habitat and conservation land are excluded. A very high fire hazard zone, earthquake fault zone, 100-year flood area or floodway is excluded unless the site meets the listed safety conditions. Historic properties are excluded too.
• Protected housing. No demolition or alteration of rent-restricted homes, or of "Housing that has been occupied by a tenant in the last three years." The owner signs a sworn statement, and the City "may conduct its own inquiries."
• Units on the lot. A lot not created by an urban lot split may have the two-unit project "plus any ADU or JADU that must be allowed under state law." A lot created by a split may have no more than two units of any kind.
• Design. New homes must match an existing house in "exterior materials, finishes, color and dominant roof pitch," use down-lights only, and have no window or door with "a direct line of sight to an adjoining residential property."
• Other conditions. All nonconforming zoning conditions must be corrected. No non-residential use and no rental under thirty days. The owner must notify adjacent owners "At least thirty business days before starting any construction."

Where Chapter 18.113 and the Statute Differ

Government Code 65852.21, as amended effective June 30, 2026, says a city "shall not impose objective zoning standards, objective subdivision standards, and objective design standards that do not apply uniformly to development within the underlying zone," unless they are more permissive. Several Rialto SB 9 rules apply only to SB 9 homes: the 800 square foot cap, the one-story and 16-foot height limit where the R-1 zones allow two and one-half stories and 35 feet, the window and landscape rules and the matching-materials rule. Each of those rules is stricter than what the R-1 zone applies to other houses. The statute also requires a decision "within 60 days from the date the local agency receives a completed application," or the project "shall be deemed approved"; Chapter 18.113 states no deadline. The statute controls on both points. Ask the Planning Division how it applies Chapter 18.113 before you design.

Where to Go Next

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

Frequently Asked Questions

Official sources (checked October 2026)