Building an ADU in San José

What you can build in San José

San José allows ADUs on residential lots with a single-family home, a duplex or a multifamily building. The main home must be legally built with approved permits. If your lot has an open Code Enforcement case, you must resolve it before the city will accept your ADU plans.

You design your ADU under one of two rule sets. The City standards are in Municipal Code Section 20.80.175. The State standards are in Section 20.80.176, which follows state law (Gov. Code 66323). The city says the standards "cannot be mixed; you must choose either all City standards or all State standards."

• City standards, single-family lot: one attached or detached ADU plus one junior ADU.
• State standards, single-family lot: one new ADU, one ADU converted from existing space and one junior ADU. You can't add a new attached ADU if you also have a conversion ADU.
• City standards, duplex or multifamily lot: one attached or detached ADU.
• State standards, duplex or multifamily lot: up to eight detached ADUs with an existing building (no more than the number of existing units), or up to two with a new building. You can also convert unused space such as attics, basements or garages into ADUs: at least one, and up to 25% of the existing units.

Tiny homes on wheels count as ADUs in San José. They are allowed only on single-family lots and follow Bulletin 291. [1][2][3]

Size, height and setbacks

City standards. A new ADU can be up to 1,000 sq ft on a lot of up to 9,000 sq ft, or 1,200 sq ft on a larger lot. An attached ADU also can't be more than 50% of the existing main home. (HCD, the state housing agency, says a percentage cap like this can't hold an attached ADU below 850 sq ft, or 1,000 sq ft with more than one bedroom.) There is no size cap when you convert an existing detached accessory building. A one-story detached ADU can be 18 feet tall. A two-story detached or attached ADU can be 25 feet tall, with no more than two stories.

Under the code, side and rear setbacks are 0 feet for the first story. The city's checklist lists 4 feet but notes that "a zero setback is allowed; however, must comply with building and Fire requirements." A second story needs 4 feet from side and rear lines. A detached ADU goes in the rear yard, or 45 feet back from the front line with a 4-foot side setback. It must be at least 6 feet from the main home. Structures can cover no more than 40% of the rear yard, but that limit can't block an 800 sq ft ADU with 4-foot side and rear setbacks. An attached ADU's front door can't be on the same street-facing wall as the main home's front door.

State standards. A new ADU can be up to 800 sq ft. It needs 4-foot side and rear setbacks. On a single-family lot, it can be 16 feet tall if detached or 25 feet if attached. Up to 2 more feet may be allowed for a pitched roof within a half mile of major transit. On duplex and multifamily lots, a detached ADU can be 18 feet tall. Converting existing space has no size cap, and up to 150 sq ft may be added for an entrance.

Every ADU must be at least 150 sq ft. San José measures livable floor space "to the exterior finish." State law now bases size limits on interior living space, so confirm how your plans will be measured with the ADU Ally.

On a historic property, the City standards add design rules from Section 20.80.175(E). The State standards add none. [2][3][5]

Parking

San José requires no off-street parking for an ADU under either rule set. If you remove or demolish covered parking to build the ADU, you don't have to replace it. State law also bars cities from requiring parking for a junior ADU, even one made from an attached garage. [2][3][6]

Fees

Your building permit fee depends on the size of your ADU. The city's Building Fee Estimator gives a general idea of permit costs. You pay initial plan review fees once your application passes prescreen. You pay the rest of the plan review fees and the inspection fees before the permit is issued.

An ADU of 750 sq ft or less pays no impact fees. An ADU of 751 sq ft or more pays school and parkland impact fees, and the city won't issue your permit until they're paid. Park fees vary by location. City staff give you a school fee referral form when you submit. Under state law, impact fees on an ADU over 750 sq ft of interior livable space must be charged in proportion to the ADU's size compared with the main home. (The city's ADU FAQ still says "less than 750 sq. ft."; its 2026 checklist and HCD's handbook say 750 sq ft or less.) HCD's handbook also says school districts may charge fees on ADUs larger than 500 sq ft, so confirm school fees with your school district.

A preliminary virtual meeting with a planner is billed at $398 per hour, with a 30-minute minimum. You can also call or email a planner with basic questions; that service does not include plan review.

Your property taxes will go up based on the value of the ADU. For typical cost ranges, see our ADU cost guide and financing guide. [2][4][5][7]

How long it takes

The first round of building review typically takes 20 business days, unless your plans need more review. The city says accurate, complete plans help you stay "within one or two plan review cycles." With a pre-approved plan on a qualifying lot, the permit may be issued on the same day as your plan review meeting.

State law sets deadlines too. The city must tell you whether your application is complete within 15 business days. It must approve or deny a complete application within 60 days when there's already a home on the lot. See our ADU permit process guide.

Get the water flow letter early. The city says "projects are often delayed because applicants do not get this letter." [4][5][7][8]

Fire safety requirements

San José's Fire Department reviews every ADU. Its checklist asks:

• Is every side of the ADU within 150 feet of the street curb, along a clear path at least 4 feet wide?
• Is the farthest wall within 600 feet of a fire hydrant?
• Does the nearest hydrant deliver at least 1,000 gpm at 20 psi? You prove this with a letter from your water company.

If you answer no, you may need a Fire Variance with extra safety measures. If your main home has fire sprinklers, the ADU must have them too. An attached ADU over 500 sq ft, where the house and ADU together exceed 3,600 sq ft, means sprinklers for both. Questions go to Fire permit staff at (408) 535-7750. [2][7]

Garage conversions and junior ADUs

You can turn a garage or basement into an ADU or junior ADU through the city's ADU Service. Under the City standards, converting an existing structure keeps its existing setbacks. Converting an existing detached accessory building has no size cap. See our garage conversion guide.

A junior ADU (JADU) must be inside the existing footprint of a single-family home, which can include an attached garage. It can also be built inside a new single-family home. It can be up to 500 sq ft. If it shares a bathroom with the main home, the owner must live on the property. For a JADU, you sign Form 313, the JADU Deed Restriction Agreement, with an ink signature and mail it in. State law allows a city to require this deed restriction for a JADU, but not for an ADU. A JADU can't be rented for 30 days or less. [2][3][4][5][9]

Renting, selling and legalizing an ADU

You can build an ADU even if the main house is a rental. You can rent the house and ADU to different people. San José can't require you to live on the property for an ADU. The city says "the minimum term for an ADU rental is 30 days, including for Airbnb rentals."

To sell an ADU separately, you must first do a condominium conversion. You fill out the city's ADU Condominium Checklist, then apply to Public Works for a Parcel Map. No condominium plan can be recorded without consent from each lender with a lien on the property.

If you have an ADU or JADU built without permits before January 1, 2020, the city's AB 2533 legalization program offers a penalty-free path. The inspection is "safety-focused," not a full code check. It typically takes 4 to 6 months from a complete application. [3][5][7][10][11]

Lot splits and duplexes (SB 9)

San José applies state law SB 9 through Part 8 of its zoning code. 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 differently: without a lot split, a lot can get up to two SB 9 units plus the ADUs and JADUs that ADU law would otherwise allow, which can add up to more than four (though then the city doesn't have to approve a later SB 9 lot split). If you want more than four units, ask the ADU Ally. After a lot split, each new lot can have at most two units, also counting ADUs and JADUs. SB 9 homes must be 4 feet from side and rear lines and no taller than 30 feet or two stories, whichever is lower. For a lot split, you sign an affidavit that you intend to live in one of the units for at least three years. You also record a deed restriction barring rentals of 30 days or less. See our SB 9 lot split guide. [5][12]

Where San José and state law differ

In December 2025, the state housing agency HCD wrote to San José. It said the latest ADU ordinance HCD had on file was from 2021 and "may be outdated." Since then, the city's code shows amendments through 2026, and its checklist (updated September 16, 2026) adds a State standards option that follows state law. Where a City standard is stricter than state law, use the State standards or ask the ADU Ally. One example is the City limit of one ADU on a multifamily lot. Other differences are the City cap of 50% of the main home for an attached ADU and the four-unit cap for SB 9 projects (both explained above). See our California ADU law overview. [2][3][5][6][12]

Permit steps in San José

1. Complete the ADU Universal Checklist

   Fill in the city's ADU Universal Checklist (Bulletin #210). Look up your property's flood, geohazard, historic and fire-zone designations on SJPermits.org. [2][4]

2. Get early feedback from a planner

   For basic questions, call a planner at (408) 535-3555 or email ZoningQuestions@sanjoseca.gov. For feedback on your specific plans, email the ADU Ally to request a preliminary virtual meeting, billed at $398 per hour with a 30-minute minimum. [4]

3. Prepare your plans and documents

   The city recommends hiring an experienced professional. Follow Bulletin 211 ADU Building Plan Requirements, and ask your water company for a hydrant flow letter early. Or choose a pre-approved plan and add a site plan. [4][8]

4. Start your application online

   Use the city's Application Wizard to find the right permit path, then create an account on SJPermits.org. Name an "ePlan Applicant", who uploads documents and answers review comments. [4]

5. Upload a complete package to SJePlans

   Upload your plans, energy and CalGreen forms, the water flow letter, Form 302 (address) and Form 312 (owner declaration). For a JADU, use Form 313 instead of Form 312. The city will not process incomplete plans. [4]

6. Go through plan review and pay fees

   Review runs in three stages: prescreen (you pay initial fees), plan review (you answer comments in SJePlans) and issuance review (you pay the remaining review and inspection fees). Impact fees for ADUs of 751 sq ft or more must be paid before the permit is issued. [2][4]

7. Build and pass inspections

   Your contractor schedules inspections. Have Bulletin #213, the approved plans and the permit card on site. Complete the Construction and Demolition Diversion sign-off before the final inspection. [4]

Pre-approved and sample plans

• Preapproved ADUs

  City-reviewed standard ADU plans from listed vendors, from about 476 to 991 sq ft. You add a site plan, and permits may be issued the same day on residential lots with a single-family home or duplex outside geohazard, landslide, flood and wildfire (WUI) zones. [8]

Who to call

• ADU Ally, Development Services Permit Center

  Questions about the ADU permit process, pre-approved plans, multifamily ADUs and legalization

  408-793-5302

  [2][4]

• Planning Division

  Zoning questions and basic information from a planner (email ZoningQuestions@sanjoseca.gov)

  408-535-3555

  [4]

• Building Division

  Building permits and inspections

  408-535-3555

  San José City Hall, 200 E. Santa Clara St., San José, CA 95113

  [2]

• Bureau of Fire Prevention

  Fire access, hydrant, sprinkler and Fire Variance questions

  408-535-7750

  [2][7]

• Public Works (AB 1033 Parcel Maps)

  ADU condominium conversions and Parcel Maps

  408-535-7802

  [10]

Questions people ask