Vallejo | ADUs and SB 9

Vallejo ADUs and SB 9: The 2026 ADU Chapter, Junior ADUs and Two Homes per Lot

An accessory dwelling unit (ADU) is a second home on a lot, with its own kitchen and bathroom. A junior ADU (JADU) is a unit of up to 500 square feet inside a house. Vallejo replaced its ADU rules in 2026: Ordinance No. 1890 N.C.(2d) repealed Chapter 16.303 of the Zoning Code and added a new one, in force since October 8, 2026. The Municode copy of the code, current through December 16, 2025, still prints the old chapter, so read this page and the ordinance instead. SB 9, the state law that allows two main homes on a house lot, has no section in Vallejo's code and applies as the statute is written. The Vallejo overview has the summary.

How the New ADU Chapter Was Adopted

HCD, the state Department of Housing and Community Development, reviews city ADU rules. On October 8, 2025 it wrote to the City that "The most recent ADU ordinance on file for City of Vallejo with the California Department of Housing and Community Development (HCD) is from 2018," that it "may be outdated and out of compliance with State ADU Law," and asked for a reply by November 7, 2025. The City's August 4, 2026 staff report gives a different date for the old rules: "The City's current ADU ordinance was adopted in 2021 and has not been updated." Both point to the same text, the chapter in the 2021 Zoning Code, which still cited the old Government Code 65852.2.

The Planning Commission recommended a new chapter on April 20, 2026. Before the Council took it up, the California Housing Defense Fund wrote that several parts conflicted with state law, and the Vallejo Flood and Wastewater District raised the sewer connection wording. Staff revised it, the Commission voted 5-0 again on July 6, 2026, and the Council introduced it on August 4, 2026. The ordinance's own certificate says it was "finally passed and adopted at an adjourned regular meeting of the City Council held the 8th day of September 2026." The City's project page says it was adopted "on September 9, 2026," that it "will go into effect on October 8, 2026," and that a copy went to HCD on September 11, 2026. The signed ordinance controls the date; both dates lead to the same October 8 start, 30 days after final passage.

ADU Types and Sizes

Source: Ordinance No. 1890 N.C.(2d), Sections 16.303.08 and 16.303.10 to 16.303.13. Front setbacks do not apply to ADUs that Government Code 66323 requires a city to approve.

The ordinance defines three kinds of ADU. A conversion ADU is made from space inside a house or an existing accessory structure, or on an apartment lot from "nonhabitable space," such as storage rooms, boiler rooms, attics, basements or garages. An attached ADU is new construction that "shares at least one wall" with the house. A detached ADU is new construction that "does not share a wall" with any home on the lot. Conversion ADUs, attached ADUs and junior ADUs each need an outside entrance of their own.

• Detached ADUs may be 16 feet tall, or 18 feet plus 2 feet for a matching roof pitch within one-half mile of a major transit stop or a high-quality transit corridor. On a lot with a multistory apartment building they may be 18 feet anywhere. The site standards of Chapters 16.501 to 16.509, such as lot coverage and open space, may not be applied so as to stop "at least one detached ADU of at least 800 square feet" with four-foot side and rear setbacks.
• Attached ADUs may be 25 feet tall or as tall as the house may be, whichever is lower, and may have an inside door to the house if they keep their own outside entrance.
• Conversion ADUs keep the height of the space converted, need no setbacks, and have no size cap. One converted from an accessory structure may grow by 150 square feet "solely for the purpose of accommodating ingress and egress."
• Junior ADUs must be "located entirely within the walls of the proposed or existing single-family dwelling," with attached garages counted as part of the house. A junior ADU needs at least an efficiency kitchen, meaning a cooking appliance, a food preparation counter and storage cabinets. If it has no bathroom of its own, it needs an inside door to the house.

How Many ADUs Fit on a Lot

Section 16.303.14 sums up the combinations. On a lot with a house: one junior ADU, plus one attached or conversion ADU, plus one detached ADU, and "the total number of ADUs and JADUs permitted on a single-family lot shall not exceed three units." So a house lot can hold four homes in all, counting the house (VanPlex arithmetic).

On a lot with apartments, the ordinance treats "two or more attached dwelling units within the same structure" as a multi-family residential lot, and it adds that "A lot with multiple detached single-unit dwellings shall not be considered a multi-family residential lot." A multi-family lot may add conversion ADUs up to 25 percent of the existing units, or at least one. A lot with existing apartments may add "up to eight detached ADUs," never more than its existing units. A lot with new or proposed apartments may add no more than two detached ADUs, built at the same time. So an existing fourplex could add up to four detached ADUs (VanPlex arithmetic). The old chapter allowed only "Up to two ADUs" in a detached structure on an apartment lot.

ADUs do not count against density. Under Section 16.303.07 a complying ADU "shall not count toward the allowable density for the lot" and "shall be considered a residential use consistent with the existing General Plan land use designation and zoning for the lot."

Design Rules for Larger ADUs

Section 16.303.09 sets local design standards that apply "only to newly constructed attached and detached ADUs that exceed 800 square feet in floor area," and never to ADUs that Government Code 66323 requires a city to approve:

• Walls, roof, eaves, windows and doors must match "the type, color range, and finish" of the house.
• The roof slope must match "the largest portion of the primary dwelling's roof," or be flat if the house roof is flat.
• A clear path at least 3 feet wide must run from the ADU entrance to the street, driveway or alley.
• Heating and cooling equipment, water heaters and other outdoor units must be screened from public view.
• An outside staircase to a second-story ADU must be at least 5 feet from side and rear lot lines.
• A detached ADU must stand at least 5 feet from the house and other structures, unless building or fire codes ask for more.

A newly built detached ADU also needs solar panels under the state Energy Code, placed on the ADU or the house. Fire sprinklers are needed only if the house already must have them, and the ADU never triggers sprinklers in the house. Each ADU gets its own address, assigned by the Public Works Department.

Approval, Parking, Rentals and Sale

• Permit. An ADU needs only a building permit, approved "ministerially, without a public hearing or discretionary decision." Ministerial means staff check the plans against fixed rules.
• Deadlines. The Building Division has 15 business days to say whether an application is complete, then sends it to the Planning Division to check the chapter's standards. A complete application must be approved or denied within 60 days, or "the application shall be deemed approved." A denial must list each defect and how to fix it.
• Appeal. An applicant may appeal an incompleteness finding or a denial in writing to the Director, who decides within 60 business days. "The decision of the Director shall be final."
• Parking. One space per ADU, which may be "tandem parking on an existing driveway," meaning one car behind another. No space is needed for an ADU of 500 square feet or less, one within one-half mile walking distance of public transit, one in a historic district, one inside the house or an accessory structure, one where street permits are not offered to its tenant, or one within a block of a car share vehicle. The staff report calls the 500 square foot exemption "additional flexibility beyond minimum State requirements." When a garage or parking space is converted or removed for an ADU, "replacement parking shall not be required."
• Owner occupancy. None for ADUs. A junior ADU with a shared bathroom requires the owner to live in the house or the junior ADU.
• Rentals and sale. Rentals must run "longer than 30 consecutive days." An ADU may not be sold separately from the house except under Government Code 66341, which covers some homes built and sold by nonprofit housing groups. Before a junior ADU gets its certificate of occupancy, the owner records a deed restriction against selling it separately.
• Unpermitted work. Fixing non-conforming conditions or unpermitted structures that do not threaten health or safety and are not affected by the ADU "shall not be required" as a condition of approval.

ADU Fees

The FY 2026-2027 Master Fee Schedule lists a Planning Division fee of $968 for an "Accessory Dwelling Unit," and building permit fees are charged on top. Several City charges exempt ADUs in the code itself: the property development excise tax (Section 3.05.040.C) and both park charges (Sections 3.18.140 and 3.18.210). Solano County's public facilities fee, collected by the City's Building Division, is listed at $4,536 per "Second / Accessory Unit."

For impact fees, Section 16.303.05.B says "Newly constructed ADUs with a total floor area of 750 square feet or greater shall be subject to impact fees," charged in proportion to the size of the house. State law draws the line one step differently. Government Code 66311.5 bars any impact fee on "an accessory dwelling unit that has 750 square feet of interior livable space or less." Under the statute, which controls, an ADU of exactly 750 square feet pays no impact fee. The ordinance's own Section 16.303.15 says state law controls where they conflict. A conversion ADU or junior ADU is not treated as a new home for water and sewer connection fees unless it is built with a new house.

ADUs in Historic and View Districts

Section 16.303.08.C applies "objective standards adopted to protect the historic character" to ADUs in a historic district, on a landmark, or on a property listed in the California or National Register, except for ADUs that Government Code 66323 requires a city to approve. The historic chapter adds that "No certificate of appropriateness is required for development or alteration of an accessory dwelling unit." A demolition permit for a garage replaced by an ADU is issued with the ADU permit; on a landmark or in a historic district, written notice or a placard on the site is required.

Section 16.213.02, for the Residential View District, still tells the Director to mail notice to owners within 200 feet before a building permit for "a new accessory structure, including an accessory dwelling unit," and to send it to the Planning Commission if a neighbor objects. State law and Section 16.303.03 require ADU approval without a hearing or discretionary decision, and Section 16.303.15 says state law controls. Ask the Planning Division how it handles an ADU in a view district.

SB 9: Two Homes on a House Lot

SB 9 (2021) requires a city to approve two main homes on a lot in a single-family zone, with no hearing. Vallejo has no local SB 9 section. Its Master Fee Schedule lists "SB-9 - Two Unit Development" at $1,737 and "SB-9 Lot Split and Two Unit Development" at $3,081, so it takes the applications under Government Code 65852.21. The statute says:

• Local standards may not "physically preclude either of the two units from being at least 800 square feet in floor area."
• A city "may require a setback of up to four feet from the side and rear lot lines," and none for an existing structure rebuilt in the same place and size.
• A complete application is approved or denied within 60 days, or "the application shall be deemed approved."
• Projects that would demolish or alter rent-restricted housing or housing occupied by a tenant in the last three years are excluded, along with the other limits explained on the SB 9 page.

Vallejo is a charter city. Its City Charter was ratified by voters on June 2, 1970, and received by the Secretary of State on August 14, 1970. The SB 9 statutes define a local agency as a city "whether general law or chartered," and the City's fee schedule shows it processes SB 9 applications. On a lot created by an SB 9 lot split, Section 16.303.08.G allows "no more than two total dwelling units," ADUs included. The lot size and subdivisions page covers the lot split itself.

Where the Ordinance and State Law Differ

• Impact fees at 750 square feet. The ordinance charges ADUs "750 square feet or greater"; Government Code 66311.5 exempts "750 square feet of interior livable space or less." The statute controls.
• Attached ADU size. Section 16.303.11 caps an attached ADU at "the lesser of" half the house or "at least 850 square feet for a studio or one-bedroom unit, or 1,000 square feet" with two or more bedrooms. Government Code 66321(b)(2) bars a maximum size below 850 or 1,000 square feet. On a small house, the statute's floor controls.
• View district review. Section 16.213.02 still routes some ADUs to notice and a hearing. The statute and Section 16.303.15 control.
• Old references. The fee chapters still define ADUs by "Section 16.04.011," a section of the zoning ordinance repealed in 2021.

Under Government Code 66326 the City sent the ordinance to HCD, which may review it and send findings. If it does, the staff report says staff will return to the Planning Commission and Council. In calendar year 2025, before the new chapter, the City issued planning approvals for 19 ADUs, according to the same staff report.

Where to Go Next

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

Frequently Asked Questions

Official sources (checked October 2026)