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Common ADU Questions
  1. Can I build a new house and ADU at the same time? Yes.
  2. Can I build an ADU where the single-family house is a rental? Yes. And can I rent the house and ADU to different parties? Yes.

  3. Can I build an ADU on a property with a duplex or apartment building? No.

  4. Can an ADU have a porch? Yes. Will the porch count in the allowed square footage for the unit?

    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.

  5. 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.

  6. Is an ADU required to have separate utilities?

    Utilities can be combined with the main residence OR can be separate.

  7. Is an ADU required to have fire sprinklers?
    • If the main house has fire sprinklers, the ADU must also have fire sprinklers.
    • If the project is an Attached ADU greater than 500 sq. ft. AND the overall gross floor area with the main house exceeds 3,600 sq. ft., then fire sprinklers are required for the entire house and ADU.
    • Sprinklers may be required for a detached ADU that is built with less than a three-foot setback.
    • There may be other circumstances when the ADU project has fire protection deficiencies, and fire sprinklers may be  required. Please see the ADU Universal Checklist, Section D. for more information.
    • For questions, call 408-535-7750 and ask to speak with a fire permit specialist.
    • 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 second unit. For more information, visit:

  1. How do I get a building permit for an ADU?

    First, use the ADU Screening Form to understand the development standards and possible permit requirements for your ADU project.

    Then create accurate and complete building plans, using Bulletin 211-ADU Building Plans Submittal Checklist as your guide for your full submittal package. Hiring a professional architect, designer, or contractor to create the plans is highly recommended. Your professional representative can submit the plans with a Building Permit Application at the Permit Center.

    Contact our ADU Ally for help with scheduling an appointment for your ADU Plan Submittal
    Phone:  408-793-5302
  2. How much is the building permit? 

    The building permit fee depends on the ADU square footage. Use our Permit Cost Estimate Worksheet to obtain a free estimate. Other fees may apply:
    • School fees
    • Park Impact fees
    • Fees for any clearances or other permits as may be applicable, such as a Geohazard Clearance, Tree Removal Permit, or a Fire Variance, for example.

  1. How long does it take to get my plans approved?

    Typically 20 business days unless your plan requires more than a first review. 

Our video, "Permits for ADUs" on YouTube may help you understand the planning, permit and plan review process: