Getting it permitted

Legalizing an unpermitted ADU or garage conversion

Checked against state laws and official agency sources · Last reviewed October 10, 2026

Why an unpermitted ADU is a problem

Seattle puts it plainly: ADUs "are not legal unless they have been established through a permit process." Cities can enforce against units that aren't legalized. Fremont, California, says legalizing protects you "from code enforcement actions such as fines, penalties, or orders to remove the structure." Bellingham, Washington, says existing unpermitted ADUs must apply to become legal, and "units that are not legalized will be subject to enforcement."

In California, you must get a certificate of occupancy before anyone lives in an ADU or junior ADU. An unpermitted unit doesn't have one. [1][2][6][7]

California: units built before 2020 (AB 2533)

Government Code 66311.7, from AB 2533 (2024), says a city or county "shall not deny a permit for an unpermitted accessory dwelling unit or an unpermitted junior accessory dwelling unit that was constructed before January 1, 2020," because it violates building standards or doesn't comply with the state ADU law or a local ADU ordinance. SB 543 (2025) renumbered it; it was section 66332 until January 1, 2026, so some city pages, including Oakland's and Fremont's, still cite the old number.

There are limits and extras:

• Health and safety comes first. The city may deny the permit if it finds that "correcting the violation is necessary to comply with the standards specified in Section 17920.3 of the Health and Safety Code," the state's list of substandard building conditions. The protection doesn't apply to a building that is substandard under that section.
• Public information. Cities must post a checklist of those substandard conditions and tell homeowners that before applying, they "may obtain a confidential third-party code inspection from a licensed contractor."
• Fees. You "shall not be required to pay impact fees or connection or capacity charges," except when utility work is needed to meet the health and safety standards and the fee is otherwise allowed.
• Inspection without penalty. After you apply, a city inspector may inspect the unit and recommend fixes. If the inspector finds health and safety problems, the city "shall not penalize an applicant for having the unpermitted" unit and "shall approve necessary permits to correct noncompliance."

Units built on or after January 1, 2020, don't get this protection. Riverside, for example, says those must be legalized with complete plans that meet the building codes in effect when you apply. [2][4][5][7][8]

The building code in effect when it was built

A 2018 California law, SB 1226, added Health and Safety Code 17958.12. It says "a building official has the discretion to apply the building standards that were in effect at the time a residential unit was constructed." When no building permit exists, the official may decide when the unit was built and apply the codes in effect then "for purposes of issuing a building permit." The law covers residential units generally, not only ADUs.

Cities apply this differently:

• Riverside applies SB 1226 to single-family homes, duplexes and ADUs built without a permit before September 30, 2018. Under its Safety-First Amnesty Program, a designer may show compliance with the codes in effect when the work was done. New alterations or additions must meet current codes.
• Los Angeles says a unit legalized under AB 2533 isn't required to meet the current California Building Standards Code, but must show it isn't substandard using the city's checklist. It "may comply with current code requirements or the codes in effect at the time the unpermitted ADU/JADU was constructed."
• Boulder, Colorado, takes the opposite approach: existing ADUs "need to be brought up to compliance with the currently adopted codes," and work that doesn't meet current code "cannot be grandfathered."

[3][8][9][10]

California: asking for a five-year delay of enforcement

If you get a notice to correct building code violations on an ADU, Health and Safety Code 17980.12 lets you ask for enforcement to be delayed for five years "on the basis that correcting the violation is not necessary to protect health and safety." It applies to ADUs built before January 1, 2020. It also applies to ADUs built later in a city whose ADU ordinance didn't comply with state law when the unit was built but complies when you ask.

The enforcement agency must grant the request if it finds the fix isn't needed for health and safety, after consulting the agency that enforces the State Fire Marshal's rules. Until January 1, 2030, the notice to correct must tell you about this right. Agencies can't approve new requests on or after January 1, 2030, but delays approved before then last their full term.

Oakland builds this into its program: once you fix life and safety violations found at the first inspection, you get "a 5 year grace period to legalize your ADU/JADU," counted from the date you applied for the enforcement delay. [5][11]

City amnesty and legalization programs in California

• Oakland: offers amnesty from Planning Code violations for ADUs built before January 1, 2021, a delay of enforcement of certain Building Code requirements for units built before January 1, 2020, and a separate AB 2533 path. You choose one program. Details: Legalize Your Unpermitted ADU or Junior ADU, or call (510) 238-3891 (Building).
• Fremont: the ADU Amnesty Program covers units built before January 1, 2020. You submit an amnesty request, a substandard housing checklist and affidavit, and proof of the build date, then pass a health and safety inspection. You then have up to five years from the inspection to apply for a building permit without penalty.
• Riverside: the Safety-First Amnesty Program uses both SB 1226 and AB 2533. You pay the applicable fees on the city's current fee schedule. Call (951) 826-5800.
• Los Angeles: LADBS bulletin P/BC 2026-150 covers converting existing buildings into ADUs and legalizing unpermitted ADUs, including the evidence it accepts that a unit was built before 2020. Some pre-2020 units fall under a separate streamlined AB 2533 bulletin, P/BC 2026-161.
• San Diego County: the County's ADU page says applicants with unpermitted ADUs built before January 1, 2020 "may be eligible to receive a permit," and points to its Substandard Structure Checklist.

Our city pages list more programs where we've found them. [2][5][8][10][12]

Outside California

The cities outside California that we checked legalize units through their normal permit process:

• Seattle: "Legalizing an existing unit" takes "a construction permit to establish use."
• Boulder: a licensed design professional must provide stamped plans, and finishes such as drywall, tile and trim will need to be removed so inspectors can check framing, insulation, plumbing, mechanical and electrical work. Existing detached ADUs need fire suppression systems.
• Bellingham: pre-existing units "must meet the same requirements as new ADUs, including building code standards."

[1][3][6]

Steps to legalize an unpermitted ADU

The details vary by city, but official programs follow a similar pattern:

• Gather proof of when it was built. In California this matters for the pre-2020 rule. Los Angeles accepts rent registration certificates, contractor bills or material receipts, utility bills or insurance documents, code enforcement records, a signed and dated lease, or real estate documents such as loan papers, an appraisal or an MLS listing. Riverside also lists county assessor records and aerial or unaltered photos.
• Consider a confidential inspection first. In California you may hire a licensed contractor for a confidential code inspection before you apply. Riverside says this inspection "is not reported to the City" and doesn't start code enforcement.
• Review the substandard checklist. California cities must post a checklist of the conditions that make a building substandard. Fremont has you fill one out, and Los Angeles reviews AB 2533 projects against its own checklist.
• Prepare plans. Riverside asks for a site plan and floor plan. Boulder requires stamped plans from a licensed design professional.
• Apply for the permit. Riverside asks you to write "AB 2533 – Legalization of Unpermitted ADU or JADU" in the permit description.
• Pass inspection and fix safety problems. Expect to correct health and safety items before the permit is finaled.

See the ADU permit process for the general permit steps, and our garage conversion and basement apartment guides for the building code issues those units often have. [2][3][4][8][10]

Questions people ask