Irvine | ADUs and SB 9
Irvine ADUs and SB 9 Duplexes: State ADU Law and Irvine's 800 Square Foot SB 9 Limit
An accessory dwelling unit (ADU) is a second, smaller home on a lot with a house. An SB 9 duplex is a project under the 2021 state law that lets an owner build two main homes on a single-family lot. Irvine treats the two in opposite ways. For ADUs it adopts state law as written, and for SB 9 it sets its own limits on size, height, renters and HOA approval. This page covers both, from the Irvine Zoning Ordinance, Supplement 16. The Irvine overview sums up the whole guide.
Irvine ADUs and SB 9 in six facts
- Irvine's ADU chapter is one sentence: ADUs are permitted and regulated under the state ADU law that begins at Government Code 66310. Source: Irvine ZO 3-26-1
- Under that state law, a detached ADU may have up to 1,200 square feet of floor area, with side and rear setbacks of no more than four feet. Source: Gov. Code 66314
- Irvine allows SB 9 duplexes only in its 2.1 Estate Density and 2.2 Low Density districts. Source: Irvine ZO 3-42-4 A
- Each Irvine SB 9 unit may have no more than 800 square feet of total floor area and one bedroom, and must be one story and 16 feet tall at most. Source: Irvine ZO 3-42-4 G, I
- An SB 9 unit the owner does not live in must be rented as affordable housing to very low, low or median income households. Source: Irvine ZO 3-42-4 P.12
- A lot in a homeowners association needs the HOA's written approval before an SB 9 duplex application can be filed. Source: Irvine ZO 3-42-4 P.10, 3-42-6
Irvine's ADU Chapter Is State Law
Chapter 3-26 of the Zoning Ordinance has one section. Section 3-26-1 reads in full: "Accessory dwellings shall be permitted and regulated in compliance with Chapter 13 of Division 1 of Title 7 of the California Government Code (Section 66310 et seq.), as may be amended from time to time." It was adopted by Ordinance 25-22 on September 9, 2025. Irvine has no local ADU size table, height table or design list in the code.
That choice has a clear result. State law says that when a city's ADU ordinance does not meet state rules, "that ordinance shall be null and void and that agency shall thereafter apply the standards established in this article" (Government Code 66316). Irvine skips that step and applies the state standards directly. The "maximum standards" for an ADU on a house lot are those in Government Code 66314, and "No additional standards, other than those provided in Section 66314, shall be used or imposed, including an owner-occupant requirement" (Government Code 66315).
ADUs are a permitted use in every Irvine residential district. Sections 3-37-12 to 3-37-16 list "Residential, accessory dwelling unit" as permitted in 2.1, 2.2, 2.3, 2.4 and 2.5. Section 1-2-1 defines an ADU as a unit with "complete independent living facilities for one or more persons," including an efficiency unit and a manufactured home, and says it "may take three forms": attached to the house, detached, or "A repurposed existing space within the principal dwelling unit." It also says "A recreational vehicle does not qualify as an accessory dwelling unit."
The State ADU Rules Irvine Applies
| Rule | What applies in Irvine | Statute |
|---|---|---|
| Detached ADU size | Up to 1,200 sq ft; a city may not cap it below 850 sq ft (1,000 sq ft with more than one bedroom) | Gov. Code 66314(d)(5), 66321(b)(2) |
| Attached ADU size | Up to 50% of the existing house | Gov. Code 66314(d)(4) |
| Side and rear setbacks | No more than 4 ft; none for a conversion in the same footprint | Gov. Code 66314(d)(7) |
| Height, detached | At least 16 ft; 18 ft within 1/2 mile walk of major transit (plus 2 ft for a matching roof pitch) | Gov. Code 66321(b)(4) |
| Height, attached | 25 ft or the house limit, whichever is lower | Gov. Code 66321(b)(4)(D) |
| Parking | At most 1 space per ADU or per bedroom; none within 1/2 mile walk of public transit and in other listed cases | Gov. Code 66314(d)(10), 66322 |
| Garage converted or removed | No replacement parking | Gov. Code 66314(d)(11) |
| Impact fees | None for an ADU of 750 sq ft or less, or a junior ADU of 500 sq ft or less | Gov. Code 66311.5(c) |
| Owner occupancy | Not allowed for ADUs; junior ADU only if it shares a bathroom with the house | Gov. Code 66315, 66333(b) |
Sources: Government Code 66314, 66321, 66322, 66311.5, 66315 and 66333, applied in Irvine by Zoning Ordinance Section 3-26-1.
A junior ADU is a unit of "no more than 500 square feet of interior livable space in size and contained entirely within a single-family residence" (Government Code 66313). It may share a bathroom with the house. Owner occupancy may be required only when it does: "Owner-occupancy shall not be required if the junior accessory dwelling unit has separate sanitation facilities" (Government Code 66333).
Some combinations must be approved by right, which means the City checks them against fixed rules and cannot add others. Government Code 66323 lists them. On a house lot, they include one ADU and one junior ADU inside the house or an existing accessory building, plus one new detached ADU with four-foot side and rear setbacks, which the City may limit to 800 square feet. On a lot with an existing apartment building, they include ADUs in unused space up to 25 percent of the existing units, plus up to eight detached ADUs, never more than the number of existing units.
ADU Parking, Fees and Timelines in Irvine
Irvine's parking table in Section 4-3-4 says: "One (1) parking space required for an accessory dwelling unit unless the accessory dwelling unit has no bedrooms, in which case, no parking space is required." The same note points to "Section 3-26-5, Parking Requirements for Accessory Dwelling Units," a section that is no longer in the code: Chapter 3-26 now has only Section 3-26-1. The one-space rule sits within the state cap of "one parking space per accessory dwelling unit or per bedroom, whichever is less," but the state exemptions in Government Code 66322 override it. No parking may be required within one-half mile walking distance of public transit, for an ADU that is part of the house or an existing accessory building, or when a car share vehicle is within one block.
Review deadlines come from Government Code 66317. The City must say whether an ADU application is complete "not later than 15 business days after" it receives it, and must approve or deny it "within 60 days" of a complete application when a house already stands on the lot.
Irvine's Schedule I planning fees, effective August 15, 2026, list "Accessory Dwelling Unit" code compliance review at $217.64 per hour, with a $1,500.00 initial deposit and a $300.00 minimum balance. The City's impact fee chapter says "Accessory dwelling units (ADUs) shall be subject to development impact fees per the Mitigation Fee Act and State law" (Section 2-7-905 F). State law bars impact fees on an ADU of "750 square feet of interior livable space or less," and above that size they "shall be charged proportionately in relation to the square footage of the primary dwelling unit."
Two smaller Irvine rules help ADU owners. The Objective Design Standards Manual for apartments does not apply: Section 3-18-2 B names "Accessory Dwelling Units" among the project types that "are not subject to the Objective Design Standards." And the affordable housing credits program in Section 2-3-6 lets the City assign credits for "The construction of accessory dwelling units that meet the City's affordability guidelines."
ADUs in HOA Neighborhoods
Many Irvine homes sit in a homeowners' association. For ADUs, state law limits what the HOA may do. Civil Code 4751 makes "void and unenforceable" any rule in a planned development that "effectively prohibits or unreasonably restricts the construction or use of an accessory dwelling unit or junior accessory dwelling unit on a lot zoned for single-family residential use," when the unit meets state ADU law. HOAs may still impose "reasonable restrictions," which the statute defines as rules that "do not unreasonably increase the cost to construct, effectively prohibit the construction of, or extinguish the ability to otherwise construct" an ADU. Read your CC&Rs and the HOA's design review rules before you design, because the HOA's approval process still applies to what it may lawfully regulate.
SB 9 Duplexes: Irvine Chapter 3-42
Chapter 3-42, added by Ordinance 22-10 on June 14, 2022, carries out Government Code 65852.21. It calls the project a "single-family residential duplex," meaning "a proposed housing development containing no more than two residential units on a single lot within a single-family residential zone." Adding one new unit to an existing house counts as two units.
| Rule | Irvine standard | Section |
|---|---|---|
| Zones | 2.1 Estate Density and 2.2 Low Density only | 3-42-4 A |
| Size | 800 sq ft total floor area (garages count) and one bedroom, at most | 3-42-2, 3-42-4 I |
| Height | 16 ft and one story | 3-42-4 G |
| Side and rear setbacks | At least 4 ft; zone front setback applies; nothing may project into a setback | 3-42-4 F |
| Parking | One garage space per unit with an EV charger, unless near transit or car share | 3-42-4 Q |
| Owner and renter | Owner lives in one unit; the other is rented as affordable housing; rentals over 30 days | 3-42-4 D, E, P.12 |
| HOA | Written HOA approval and a certified copy of any CC&Rs with the application | 3-42-4 P.10, 3-42-6 |
| Design | Same materials, colors and roof pitch as the house; rooftop solar; no roof decks or balconies | 3-42-4 P |
Source: Irvine Zoning Ordinance Chapter 3-42 (Ordinance 22-10), Supplement 16.
The size cap is tighter than it first looks. Section 3-42-2 defines "Total floor area" as "inclusive of all habitable areas and non-habitable areas of the structure, including but not limited to stairways, hallways, basements, attics, garages, storage areas, restrooms." With one garage space required for each unit outside the transit and car share cases, the garage counts toward the 800 square feet.
The chapter also sets rules on the lot as a whole. Each unit needs "separate, direct, and independent public services and utilities, including separate connections and meters," with electric lines underground. Each lot needs at least "ten feet" of street frontage for a driveway, or "16-foot frontage if the driveway serves two units," and the lot is "limited to one driveway ingress/egress." No window or door of a new unit may have "a direct line of sight to a window or door of a structure on an adjoining residential property," though fencing, plants or privacy glass may screen it. Every unit needs a rooftop solar system, and "No roof decks or balconies shall be constructed above or upon a single-family residential duplex."
The applicant must send written notice to owners of adjoining residential lots before or when applying. The code says this notice gives neighbors no right to comment: "Approval is ministerial," meaning staff check it against fixed rules without a hearing. The Community Development Director reviews the permit, which "shall also serve as the building permit."
Owner Occupancy, Affordable Rent and the Deed Restriction
Irvine adds occupancy rules to every SB 9 duplex. "One of the units in the single-family residential duplex located on a parcel shall be occupied by the owner of the parcel as the owner's primary residence." The other unit, if not the owner's home, "shall be rented as affordable housing to people of very low, low, or median income, as those terms are defined in Chapter 2-3." No unit may be rented "for less than 30 days."
These rules are recorded. Before the permit, "A deed restriction prepared by the City shall be recorded on the subject property," and it "runs with the land," which means it binds every later owner. A buyer of an Irvine lot with an SB 9 duplex takes on the owner occupancy and affordable rent terms.
HOA Approval Comes First
Irvine makes the HOA the first stop. If the lot is in an HOA, "the applicant shall submit to the City written evidence of the HOA's approval of the single-family residential duplex prior to submitting" the application. Section 3-42-6 adds that the applicant must file "a certified copy of said CC&Rs" and a confirmation "signed by the president or equivalent on behalf of the homeowners' association." The City "may deny" the permit if the CC&Rs prohibit the duplex or the HOA does.
The code is plain about private rules: "Nothing in this chapter shall be construed to prevent CC&Rs or a homeowners' association from prohibiting, restricting, or otherwise imposing rules on single-family residential duplexes." The Civil Code protection for ADUs above covers ADUs and junior ADUs only. So in an Irvine HOA, an ADU is protected by state law, and an SB 9 duplex depends on the HOA.
Where Irvine's SB 9 Text and State Law Differ
Chapter 3-42 dates from 2022. Government Code 65852.21 was last amended by SB 1426, effective June 30, 2026, and its current text differs from the City chapter in four places. Where they conflict, the statute controls. Ask the Planning Division how it applies Chapter 3-42 today.
- Uniform standards. The statute 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." The 16-foot, one-story and 800 square foot limits in Section 3-42-4 apply to SB 9 units only; the 2.2 district allows 35 feet for other homes.
- Grounds for denial. The City text lets the Director deny for a specific adverse impact on "public health and safety or the physical environment." The statute allows denial for an impact "upon public health and safety" only.
- Deadline. The statute requires a decision "within 60 days" of a complete application, after which "the application shall be deemed approved." Chapter 3-42 sets no deadline.
- Minimum size. The statute bars standards that "would physically preclude either of the two units from being at least 800 square feet in floor area." Irvine counts garages in its 800 square foot cap. Section 3-42-4 S lets the Director grant "the minimum deviation" needed to allow two units of at least 800 square feet, but never for the side and rear setbacks.
Both texts bar an SB 9 duplex that would require tearing down or altering housing a tenant lived in during the past three years, and Irvine's text adds a cap of 25 percent on demolishing exterior walls in that case. Both also let a city refuse an ADU on a parcel that uses both the duplex and the lot split, and Irvine does, in Section 3-42-5. The lots and subdivisions page covers the lot split, and the state SB 9 page explains the statute.
Best For
- ✓ Any Irvine house lot with room for a detached ADU of up to 1,200 square feet.
- ✓ Garage or spare room conversions, which need no replacement parking.
- ✓ Owners in an HOA, since state law protects ADUs from HOA bans.
Usually Fails When
- ✕ The plan is a market-rate SB 9 rental, since the non-owner unit must be affordable.
- ✕ The HOA or CC&Rs bar an SB 9 duplex.
- ✕ The lot is zoned 2.3 or higher and the plan relies on Chapter 3-42.
What To Verify Before Spending Money
- → Your CC&Rs and HOA approval process.
- → Transit distance, which removes ADU and SB 9 parking.
- → How the Planning Division applies Chapter 3-42 after the June 30, 2026 change to state law.
Where to Go Next
Related on VanPlex: the California ADU law page, the SB 9 page and the Irvine overview.
Frequently Asked Questions
What are the ADU rules in Irvine?
How big can a detached ADU be in Irvine?
Do I need a parking space for an ADU in Irvine?
Can my HOA in Irvine stop me from building an ADU?
Where are SB 9 duplexes allowed in Irvine?
How large can an SB 9 unit be in Irvine?
Can I rent out the second SB 9 unit in Irvine at market rent?
Can I add an ADU to a lot with an SB 9 duplex in Irvine?
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What does Irvine charge to review an ADU?
Official sources (checked October 2026)
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