Building an ADU in San Jose: Rules, Permits, Pre-Approved Plans, Costs

Yes, you can build an ADU in San Jose on almost any lot with a single-family home, a duplex or a multifamily building. On a typical single-family lot the City allows a detached or attached ADU of up to 1,000 square feet (1,200 on lots over 9,000 square feet), with 4-foot side and rear setbacks and no parking requirement. You can also add a junior ADU (JADU) of up to 500 square feet inside the house. Permits run through SJPermits.org. In our current guidance, most San Jose ADUs cost between $150,000 and $400,000 depending on the type.

This guide covers the types of ADUs, the City and State rules, the permit steps, the City’s preapproved plan program, fees, and what you can and can’t do once the unit is built: rent it, live in it, or sell it.

What Counts as an ADU in San Jose? ADU vs JADU

The City of San José defines an accessory dwelling unit as a small, independent home on a residential lot, with its own kitchen and bathroom. They are allowed on single-family, duplex and multifamily properties. You will usually be choosing between four types:

Detached ADU. A new, freestanding building, usually in the backyard. Often called a backyard cottage or granny flat.
Attached ADU. A new addition that connects to the main house, such as a unit built off the back of the home or over an attached garage.
Conversion ADU. Existing space turned into a unit: a detached garage, an attached garage, a basement or part of the house. Converting a garage into an ADU is common in San Jose because the walls, roof and slab already exist.
Junior ADU (JADU). A unit of no more than 500 square feet built inside the walls of a single-family home, which can include an attached garage. A JADU needs at least an efficiency kitchen and may share a bathroom with the main house.

The practical difference between an ADU and a JADU comes down to size, where it sits, and owner-occupancy. An ADU can be detached and has no owner-occupancy requirement. A JADU must be inside the house, and if it shares a bathroom with the main home, the owner has to live on the property (in either the house or the JADU). The City also requires a recorded JADU deed restriction, which blocks selling the JADU separately from the home.

San José also permits tiny homes on wheels as a type of ADU on single-family lots, with a separate, simpler checklist (Bulletin 291).

San Jose ADU Requirements: Size, Height and Setbacks

San José gives you a choice. You design the ADU under either the City development standards (Municipal Code 20.80.175) or the State development standards (20.80.176), and you can’t mix the two. The City’s ADU Universal Checklist (Bulletin 210) sets them side by side. Here is a summary for single-family properties, based on the version updated September 16, 2026:

Standard	City option: detached ADU	City option: attached ADU	State option: new ADU	JADU
Maximum size	1,000 sq ft (lots under 9,000 sq ft); 1,200 sq ft (lots over 9,000 sq ft)	Up to 50% of the main home, capped at 1,000 or 1,200 sq ft by lot size	800 sq ft	500 sq ft
Minimum size	150 sq ft	150 sq ft	150 sq ft	150 sq ft
Side and rear setbacks	4 ft (1st and 2nd story)	4 ft	4 ft	None (inside the house)
Maximum height	18 ft one story; 25 ft two story	25 ft	16 ft detached (up to 2 ft more near major transit); 25 ft attached	N/A
Stories	Up to 2	Up to 2	Up to 2	N/A
Parking	None	None	None	None

A few details in the checklist catch people off guard:

Siting under City standards. A detached ADU goes behind the main home, or behind the zoning district’s front setback. Structures (not counting pools) can cover no more than 40% of the rear yard, and you need at least 6 feet between the ADU and the main house.
Zero setbacks. The checklist notes a zero side or rear setback is possible, but only if the design meets building and fire code requirements.
Front setback flexibility under State standards. If nothing else fits, an ADU can reach into the front setback to allow at least an 800-square-foot unit.
Conversions. Converting existing space has no size cap under State standards, and you can add up to 150 square feet for an entry or exit.
Bedrooms and bathrooms. There’s no set maximum. The layout just has to meet building and fire codes.

Before you design anything, look up your property on SJPermits.org and answer Parts 1 and 2 of the checklist. Flood zones, geohazard or landslide zones, Wildland-Urban Interface areas, historic listings, easements and heritage trees can all change what you’re allowed to build and how.

How big can you make an ADU in California?

State law sets a floor that cities can’t go below. According to HCD’s ADU Handbook (March 2026), a city’s maximum size must allow at least 850 square feet, or 1,000 square feet for an ADU with more than one bedroom. Where a city has no compliant ordinance, the state default is 1,200 square feet for a new detached ADU. Cities are free to allow more, and San José’s City option allows up to 1,200 square feet on larger lots.

What State Law Says (Gov. Code 66314 and Onward)

California’s ADU rules used to live in Government Code section 65852.2. Senate Bill 477 renumbered them as of March 25, 2024, so current citations start at section 66310, with ADU approvals in 66314 onward and JADU rules in 66333 onward. If you find an older article citing 65852.2, the rule may still be in force under a new number. The main protections for homeowners:

Ministerial approval. ADUs and JADUs must be approved or denied without a public hearing or discretionary review, based only on objective standards.
Review deadlines. The permitting agency must tell you in writing whether your application is complete within 15 business days, and must approve or deny a complete application within 60 days. If it denies the application, it has to give you a full list of corrections.
Setbacks capped at 4 feet from side and rear lot lines for new ADUs. There’s no setback requirement for a conversion or for a new structure built in the same place and to the same size as an existing one.
No minimum lot size.
No owner-occupancy requirement for ADUs (JADUs are different, as noted above).
Fire sprinklers are required in an ADU only if the main house is required to have them.

State law also allows certain combinations on one single-family lot, such as a conversion ADU, a new detached ADU of up to 800 square feet, and a JADU. How those combine in San José depends on which standards you choose. The checklist footnotes, for example, bar an attached ADU when there’s an existing or proposed conversion ADU. Confirm your combination with the City before you design.

The San Jose ADU Permit Process, Step by Step

ADU permits are handled by the City’s Planning, Building and Code Enforcement department through the Development Services Permit Center. The City lays out six steps:

Complete the ADU Universal Checklist. This confirms whether your property qualifies and which standards apply. For basic questions you can call a City planner at 408-535-3555 or email ZoningQuestions@sanjoseca.gov. For project-specific feedback, you can request a preliminary virtual meeting through the ADU Ally, billed at the Planning Division’s hourly rate of $398 with a 30-minute minimum.
Prepare construction plans. The City recommends working with an experienced professional and reading Bulletin 211 (ADU Building Plan Requirements), the ADU inspection checklist and the fire requirements before drawing.
Start the online application. Use the Application Wizard, create an SJPermits.org account, and name an “ePlan Applicant” who uploads plans and answers reviewer comments.
Upload plans and documents to SJePlans. The package includes Title 24 energy calculations, the CALGreen checklist, a geotechnical report if needed, an address assignment request (Form 302), and the ADU Property Owner Declaration (Form 312). For a JADU you use Form 313, the JADU Deed Restriction Agreement, which needs a wet signature.
Plan review. After prescreening you pay the initial plan review fees, respond to comments in SJePlans, and pay the remaining fees before the permit is issued.
Construction and inspections. Your contractor schedules inspections. Before the final building inspection, you need a Construction and Demolition Diversion sign-off.

According to the City’s ADU FAQs, the first round of building review typically takes 20 business days, and complete, accurate plans help you finish in one or two review cycles.

Common mistakes that slow down a San Jose ADU

Getting the water flow letter too late. The City requires a letter from your water company showing hydrant flow near your lot, and it says projects are often delayed because applicants don’t get it. Request it early.
Not checking fire access. The Fire Department checks whether every part of the ADU is within 150 feet of the street curb along a clear path at least 4 feet wide, and within 600 feet of a hydrant. If it isn’t, you may need a fire variance and extra safety measures.
Assuming no sprinklers. If the main house has fire sprinklers, the ADU needs them too. An attached ADU over 500 square feet can also trigger sprinklers for the whole house once the combined floor area passes 3,600 square feet.
Forgetting the address. Both the main home’s address and the ADU’s unit number must be visible from the street.
Mixing City and State standards. You have to choose one set and follow all of it.

San Jose Pre-Approved ADU Plans: How the Program Works

San José runs a Preapproved ADU program in which outside vendors submit standard (not site-specific) building plans that City staff have already checked for code compliance. The City calls these plans the fastest and lowest-cost permit path, and a dedicated City review team handles them.

Here’s what you need to know:

Eligibility. The lot must be zoned residential with an existing single-family home or duplex. It must not be in a geohazard, landslide or flood zone, or a Wildland-Urban Interface area.
You still need a site plan. Preapproval covers the building, not your lot. You still submit site-specific documents showing where the ADU goes, the utility connections, setbacks and other zoning items.
Same-day permits are possible. If the site plan and documents are complete and accurate, the City says the permit may be issued on the day of the plan review meeting. Deferred structural submittals, clearances or variances can take longer.
Plans come from vendors on the City’s list. The City publishes the approved vendors and plans, plus a separate list of plans still under review that aren’t yet eligible for expedited review. Check the City page for the current list, and confirm who will pull the permit. The City strongly advises having the vendor or a contractor do it.

A 2023 state law, AB 1332, required cities to set up a preapproval program like this by January 1, 2025. Preapproved plans suit a standard backyard unit. If your lot is unusual, if you want a garage conversion or an attached unit, or if a set floor plan doesn’t fit your family, custom plans may be the better route.

ADU Cost in San Jose

In our current guidance, an ADU in San Jose typically costs $150,000 to $400,000, depending on the type. A garage conversion usually sits at the lower end because the structure already exists. A new detached ADU with its own foundation and utility runs usually sits at the higher end. For a garage conversion scoped as living space rather than a full ADU (a home office or extra bedroom, for example), the typical range we see is $40,000 to $120,000 or more. The San Jose remodeling cost guide shows how other projects compare.

The things that move an ADU budget most are the type and size of the unit, how far utilities have to run, site work such as trees and access, fire requirements like sprinklers or a variance, and finish level.

Is it cheaper to build an ADU or an addition?

It depends on what you need the space for. A room addition typically runs $300 to $600 per square foot in our current guidance (roughly $120,000 to $240,000 for 400 square feet). An addition can’t be rented as a separate unit, while an ADU can. An ADU also comes with state fee exemptions and a guaranteed ministerial review. The trade-offs are covered in detail in ADU vs home addition, and you can read more about room additions if extra space for your own household is the goal.

ADU Fees in San Jose and Impact-Fee Exemptions

Your building permit fee depends mostly on the ADU’s size, and the City offers an online Building Fee Estimator. On top of that, you may pay school fees, parkland fees, and fees for geologic hazard clearance, tree removal or a fire variance if your project needs them.

Size makes a real difference:

Under 750 square feet. State law exempts ADUs with 750 square feet or less of interior livable space from impact fees charged by local agencies, special districts and water corporations. The City’s FAQ says parkland and school fees don’t apply to ADUs under 750 square feet.
Over 750 square feet. Impact fees are charged in proportion to the ADU’s size compared with the main house. HCD’s example: a 1,000-square-foot ADU next to a 2,000-square-foot home could pay 50% of the fee for a new home. Contact your school district about its ADU fees.
JADUs of 500 square feet or less are also exempt from impact fees.
Utility connection fees. Conversions of existing space and JADUs can’t be treated as a new residential use for utility connection fees, unless they’re built at the same time as a new single-family home.

Will my property taxes go up if I build an ADU?

Yes. The City’s FAQ says your property taxes will increase based on the value of the ADU. For details, check with the Santa Clara County Assessor.

What is the $40,000 ADU grant in California?

That’s the CalHFA ADU Grant Program, which reimbursed qualifying homeowners up to $40,000 for predevelopment costs such as plans, permits, soil tests, impact fees and surveys. HCD’s March 2026 Handbook notes that the funds had been exhausted at the time it was written. Check CalHFA directly before counting on a grant.

Do You Need Parking for an ADU in San Jose?

No. The City’s checklist lists no parking requirement for ADUs or JADUs under either set of standards. State law also bars cities from requiring replacement parking when you convert or demolish a garage, carport or parking space to build an ADU. That’s a big reason garage conversions in San Jose are so popular.

Renting, Living In and Selling an ADU in San Jose

Rental rules

You can build an ADU even if the main house is a rental, and you can rent the house and the ADU to different tenants. State law lets cities set a minimum rental term, and San José applies a 30-day minimum, which rules out nightly short-term rentals. Fair housing laws apply, and the City notes you can’t refuse housing vouchers. The City also notes that PG&E now requires ADUs to have their own utility meter, while JADUs don’t need separate meters.

Owner-occupancy

ADUs have no owner-occupancy requirement. AB 976 made that permanent. JADUs are the exception: if the JADU shares a bathroom with the main home, the owner has to live on the property.

Can you sell an ADU separately in San Jose? (AB 1033)

Yes, under specific conditions. AB 1033, effective January 2024, lets cities adopt ordinances allowing an ADU to be sold separately as a condominium. In June 2024 the San José City Council adopted Ordinance No. 31095, and in August 2025 the City announced it had approved the first ADU condominium in California. The process, described on the City’s ADU Condominium Conversions page, involves:

Completing the ADU Condominium Checklist (only permitted ADUs that meet every condition qualify).
Applying for an AB 1033 Parcel Map through the Public Works Department.
Recording the parcel map, condominium plan, HOA documents and CC&Rs. State law also requires a safety inspection and lender consent before recording.
Getting a new address for the ADU using Form 302.

A JADU can’t be sold separately from the home.

Frequently Asked Questions

Can I build an ADU on any lot in San Jose?

Most residential lots with a single-family home, duplex or multifamily building qualify, and state law allows no minimum lot size. Flood, geohazard and fire zones, easements and historic status can add requirements, so start with the ADU Universal Checklist.

How long does it take to get an ADU permit in San Jose?

The City says the first round of building review typically takes 20 business days. Preapproved plans with a complete site plan can be permitted on the day of the review meeting. State law requires a decision on a complete application within 60 days.

Can I build both an ADU and a JADU?

On a single-family lot, generally yes. For example, you could have a detached ADU in the backyard and a JADU inside the house. Which combinations are allowed depends on whether you use City or State standards, so confirm yours with the City.

Can I Airbnb my ADU in San Jose?

Not on a nightly basis. San José applies the state-allowed 30-day minimum rental term to ADUs, including listings on Airbnb.

Do I need solar on a new ADU?

Newly built detached ADUs are generally subject to the California Energy Code solar requirement, with some exceptions. Conversions and attached additions are not. The panels can go on the ADU or on the main house.

Planning an ADU in San Jose?

Brother & Brother Builders is a family-owned general contractor (CSLB #887389) in business since 2006, with design, 3D renderings and permits handled in-house. If you’re weighing a detached unit, an attached unit or a conversion, our ADU construction team works throughout San Jose and the South Bay. Contact us to talk through your lot and your options.