Updates on City of San José Services and/or Operations . (English | Español | Tiếng Việt | 中文)


If you have questions about the ADU permitting process, please reach out to our ADU
Ally at the Permit Center:

ADU Ally

Common Questions about ADUs

The ADU Universal Checklist will answer many questions about:

  • Which lots qualify for an ADU and where you can locate the ADU on your lot
  • Setback, height, and fire requirements
  • Getting a building permit and plan review

In addition, here are answers to questions that we frequently hear. For additional questions and information, please contact the ADU Ally at at or 408-793-5302.


  1. What is the total cost for an ADU?
    It will depend on the size and type of ADU. A new, custom-built detached ADU may cost as much as $250,000. Retrofitting an existing attached garage or basement may cost approximately $80,000 to $150,000, depending on size, existing plumbing, and how you design the space.

  2. How might I save money on the construction cost of an ADU?
    • Consider installing a pre-fabricated unit or a tiny home on wheels (THOW).
    • Select a plan that has been pre-approved by the City.
    • Units less than 750 sq. ft. will cost less to build, and in accordance with state law, as of Jan. 1, 2020, these smaller units will not be subject to impact fees such as parkland and school fees.  

  3. Where can I find information about the cost of a building permit and any other fees?
    The building permit fee depends on the square footage of the ADU. City staff will provide you with a free estimate if you complete the Permit Cost Estimate Worksheet. Other fees may apply; please see the ADU Fees page. 
    • .

  4. Will my property taxes increase if I build an ADU?
    Yes. The primary house will not be reassessed, and your base assessment of the primary house will not be affected, but your taxes will increase based on the value of the ADU. For more information, visit:

  5. How can I finance my backyard unit?
    Many homeowners take out a home equity loan, renovation loan, or a cash-out refinance loan.


Please see the ADU Universal Checklist that provides tables for a comprehensive look at how new state laws allow for ADUs on single-family, duplex, and multifamily properties.

  1. Can I build a new house and ADU at the same time?

  2. Can I build an ADU on a property with a duplex or apartment building?
    Yes, as of Dec. 17, 2019 the City's ADU Ordinance now allows ADUs on duplex and multifamily properties. 

  3. Can I build an ADU on the side of my house or in the front yard?
    An attached ADU can be built on any side of the house, but front and side setback rules will apply. Properties with historic designations can only build the attached ADU on the rear side. See the ADU Universal Checklist for more information.

    A detached ADU, at this time, can only be built in the backyard. The City is currently working on an Ordinance update that would allow a detached unit to be built outside of the rear yard as long as it is at least 45 feet from the front property line and maintains a minimum 5-foot setback from the side yard. There are also rules about the distance of the ADU to the main home. See the ADU Universal Checklist for more information, or speak with a Planner at 408-535-3555.


  1. Can I build an ADU where the single-family house is a rental?

  2. Can I rent the house and ADU to different parties?

  3. Can I rent the ADU to whomever I choose?
    A homeowner has the right to rent their ADU to anyone they choose, however, as a landlord you must comply with fair housing laws. You cannot establish discriminatory terms or conditions in the rental advertising or agreement. You cannot advertise or establish that the unit is available or not available to people of a certain race, color, religion, sex, handicap, familial status, or national origin, and you cannot refuse housing vouchers.

    Per new state laws, the term for an ADU rental is a minimum of 30 days, including for Airbnb rentals.

    Learn more about being a landlord at the Renters & Landlords webpage:

  4. Is an ADU required to have its own address?
    Yes. An address will be assigned to the ADU as part of the building permit process.

  5. Is an ADU required to have separate utilities?
    Utilities can be combined with the main residence OR can be separate.

  6. Can an ADU have a porch, and does the porch count in the allowed square footage for the unit?
    ADUs can have a porch. If the porch is uncovered, it will not count toward the maximum floor area allowed. If the porch is covered and is 50% or more enclosed with walls, then it will count toward the allowable floor area of the ADU.


  1. How do I get a building permit for an ADU?
    We highly recommend hiring a professional architect, designer, or contractor to create the building plans that are necessary to obtain a permit. This professional can submit the plans with a Building Permit Application at the Permit Center. City staff will review the plans for compliance with the building code; if approved and all fees are paid, they will issue a building permit. Contact our ADU Ally for help with the permit process: or 408-793-5302.

  2. How long does it take to get my plans approved?
    Typically 20 business days unless your plan requires more than a first review.