Building an ADU in Fremont

What you can build in Fremont

Fremont allows ADUs on lots with an existing or proposed single-family or multifamily home in residential and mixed-use zones, and in planned districts that allow homes. The rules are in Fremont Municipal Code 18.190.005, last amended in May 2026. The code says state law prevails if the two conflict. In June 2026, the state housing agency HCD found Fremont's ADU ordinance substantially compliant with state ADU law.

An ADU can be attached to your home, built inside it (including an attached garage), or detached, including a detached garage conversion. On a single-family lot, the city's general rule is one ADU plus one junior ADU. The handout notes you can get more if you qualify under state law. The code's "statewide exemption" units can be combined: one ADU and one JADU within the existing or proposed space of the home (or an existing accessory structure), plus one new detached ADU of up to 800 sq ft with 4-foot side and rear setbacks. Confirm your combination with the Planning Division.

On a multifamily lot, you can convert non-living space such as storage rooms, attics, basements or garages into ADUs: at least one, and up to 25% of the existing units. You can also add up to eight detached ADUs with an existing multifamily building (no more than the number of existing units), or up to two with a proposed one. [2][3][4]

Size, height and setbacks

New floor area. A new attached ADU can be up to 1,000 sq ft of interior livable space. A new detached ADU can be up to 1,200 sq ft. Garages, carports, covered porches and other accessory structures don't count toward that size. Rooftop decks are not allowed.

An attached ADU can be 30 feet tall or the height limit of your zone, whichever is lower. A detached ADU on a single-family lot can be 16 feet tall, or 18 feet within a half-mile walk of a major transit stop or high-quality transit corridor. Two more feet are allowed for a roof pitch that matches the main home. New ADUs need 4-foot side and rear setbacks and the same front setback as the main home, unless that would block a statewide exemption ADU.

Conversions. An ADU made from existing floor area has no size or height limit and needs no setbacks. You can add up to 150 sq ft if needed for an entrance.

Building code spacing. The city's handout says an attached ADU needs one-hour fire-rated walls and floors between the units. For a detached ADU, it generally means keeping 5 feet from the fire separation line (10 feet between the house and the ADU), unless sprinklers or wall design allow less. Ask the Building Division at (510) 494-4460.

An ADU must have its own outside entrance and its own address. ADUs don't count toward your lot coverage limit. The city doesn't limit the number of bedrooms. [2][3]

Parking

Fremont requires no extra parking for an ADU. If you demolish or convert a garage, carport or parking space to build an ADU, you don't have to replace it. A junior ADU needs no parking under state law. [2][3][5]

Fees

The city's handout says "ADUs are not subject to development impact fees, regardless of size." The city's impact fee chapter is worded more narrowly: FMC 18.290.110 exempts ADUs from impact fees "for any remodel or addition, as long as they do not result in a change of use." State law, as HCD explains it, exempts ADUs of 750 sq ft of interior livable space or less. If you plan a new ADU over 750 sq ft, confirm with the Planning Division whether impact fees apply. You still pay permit fees. Utility agencies may charge connection fees, and the Fremont Unified School District may charge school fees, so contact them for current rates. HCD's handbook says school districts may charge fees on ADUs over 500 sq ft.

With a preapproved plan, you pay a flat $1,000 plan review fee, plus construction and inspection fees that depend on the plan.

New or separate utility connections may be needed. The city suggests contacting PG&E, the Alameda County Water District and the Union Sanitary District early. The handout notes that PG&E requires a separate electric meter for an ADU. Under the code, an ADU made inside existing space can't be required to get a new utility connection or pay a connection fee unless it is built with a new home. For typical costs, see our ADU cost guide. [2][3][5][6][7]

How long it takes

Fremont's code says the city must tell you within 15 business days whether your application is complete, and list anything missing. It must issue the permit within 60 days of a complete application if a home already exists on the lot. If you ask for a delay in writing, the 60 days pause.

The city reviews applications with preapproved plans in 7 business days, compared with 15 business days for standard applications. You can ask for the design review permit and the building permit to be reviewed at the same time. Keep your ADU on its own permit: the city rejects permit requests that combine ADU work with work on the main home. See our ADU permit process guide. [1][2][3][7]

Garage conversions and junior ADUs

You can convert an existing garage into an ADU without replacing the parking spaces. A converted ADU has no size cap. See our garage conversion guide.

A junior ADU (JADU) can be up to 500 sq ft of interior livable space. It must be entirely inside a single-family home, which can include an attached garage. It needs an efficiency kitchen and its own outside entrance and address. It can share a bathroom with the home or have its own. You can build one JADU per lot. If the JADU shares a bathroom, the owner must live in the home or the JADU. You must file a deed restriction that bars selling the JADU separately and limits its size and features. A JADU can't be rented for less than 30 days. [2][3]

Renting, selling and legalizing an ADU

You don't have to live on the property to build or rent an ADU. An ADU or JADU can't be rented for less than 30 days. You can rent an ADU separately from the main home, but you can't sell it separately, except under Gov. Code 66341.

If you have an ADU or JADU built without permits before January 1, 2020, the city's ADU Amnesty Program offers a path to legalize it. You submit an amnesty request, a substandard housing checklist and affidavit, and proof of the build date, then pass a health and safety inspection. Conditions that affect health and safety must be fixed. For other violations, you have up to five years without penalty to make improvements and get a building permit. Questions go to the Building and Safety Division at (510) 494-4460. [2][3][8]

Lot splits and duplexes (SB 9)

Fremont applies SB 9 through Section 18.190.007. Without a lot split, the city's code caps the lot at four units in total, counting ADUs and JADUs. HCD's handbook reads state law to allow, without a lot split, up to two SB 9 units plus the ADUs and JADUs ADU law would otherwise allow. If you want more than four units, ask the Planning Division. After a lot split, each new lot can have no more than two units, including ADUs and JADUs. SB 9 homes need 4-foot side and rear setbacks, but none for an existing legal structure. For a lot split, you sign an affidavit that you intend to live in one of the units for at least three years. Units can't be rented for less than 30 days. See our SB 9 lot split guide. [3][5]

Permit steps in Fremont

1. Check the rules and ask questions

   Read the city's ADU Informational Handout. Call the Zoning Line at (510) 494-4455 or email planinfo@fremont.gov. [1][2]

2. Choose a design

   Hire a designer, or contract with a designer whose plan is on the city's preapproved ADU list. Preapproved plans still need site-specific plans, studies and engineering. [7]

3. Call the utilities early

   Contact PG&E, the Alameda County Water District and the Union Sanitary District about service, fees and timelines. PG&E requires a separate electric meter for an ADU. [2]

4. Apply online

   Submit through Citizen Access. An ADU needs a Ministerial Design Review Permit, a Building Permit and a new address. To have design review and the building permit reviewed together, choose "Apply for Permit", then "Building". File the ADU as its own permit, separate from any work on the main home. [1][2]

5. Go through review

   The city must tell you within 15 business days whether your application is complete. It must issue the permit within 60 days of a complete application when a home already exists. Preapproved plans are reviewed in 7 business days. [3][7]

6. Pay fees and build

   Pay permit fees and any utility and school fees. For a JADU, file the deed restriction with the city. Then build the ADU under your building permit. [2][3]

Pre-approved and sample plans

• Preapproved ADU Program

  City-preapproved detached ADU plans from private designers, reviewed in 7 business days with a $1,000 flat plan review fee. Plans made under the 2022 building codes became invalid on January 1, 2026; the current list has one 499 sq ft plan, with more being updated. [7]

Who to call

• Planning Division (Zoning Line)

  ADU rules, design review and preapproved plans (planinfo@fremont.gov)

  510-494-4455

  [1][2]

• Building and Safety Division

  Building permits, building code questions and the ADU Amnesty Program (bldinfo@fremont.gov)

  510-494-4460

  39550 Liberty Street, P.O. Box 5006, Fremont, CA 94537-5006

  [2][8][9]

Questions people ask