Phase 5


  • Understand what’s required in your permit application
  • Know what to expect from application review
  • Get started on your application
  • Understand the types of fees you may need to pay

The permitting process can be straight-forward if you are prepared and understand what to expect. You should have an idea of how the process works from your conversations with County staff, and your designer should be familiar as well. Permitting starts with an application package and ends with a building permit, which allows you to start construction.


The Permitting phase typically takes 1-6 months. Most ADU projects take 12-18 months to complete, but some extend to 24 months or more.

Frequently Asked Questions

Here are a few of the most frequently asked questions about permitting. See the content below and your County’s ADU Guidebook for more guidance, resources, and tips for all steps of the process.

Submitting an application is different in each county. Some have online portals while others ask for multiple sets of paper copies on various sizes of paper. Some may require one application package, while others require separate review by the Planning and Building departments. Check with local staff to confirm the application process and requirements and for details about permit materials.

If you are connected to a municipal sewer system you may be required to upsize service and or meters to meet capacity requirements. Check County ADU Rules and talk with staff to learn more about local requirements for sewer connections. ADUs on properties with septic often need separate waste treatment and your existing system may need to be modified. Wells also may need special permits and review. Contact your Environmental Health Department early in the process. For contact information, see the Contact page.

In most cases, state law no longer allows cities and counties to comment on pre-existing zoning issues unrelated to the ADU. For example, you should not receive comments about correcting the main house or a fence unrelated to the ADU, unless there is an obvious public safety issue.

State law says an ADU permit cannot be denied due to nonconforming zoning, building code violations or unpermitted structures unless there is a threat to public health or safety, and they are not affected by building the ADU.

Existing unpermitted ADUs can go through the permitting and approval process set out in your County Guidebook. Planning staff will work with you to determine what would be involved to bring your ADU up to code. To note, if you constructed your ADU within the last ten years, you will be required to submit an engineer’s report and a Title 24 Energy Report.

For unpermitted ADUs built before January 1, 2018, state law says a permit to legalize cannot be denied even if there is a violation of ADU laws or building standards, unless it is a “health and safety concern” or if the building is deemed “substandard” by state Health and Safety Code.

To see translated Spanish FAQs, head to All FAQs.

Permitting, Step-by-Step

It’s helpful to talk with County staff before submitting your application. While not required, meeting with your designer and staff before you submit your application might save time later in the process. Contact staff and check out our Exercises for help with what to ask.

Read your County Guidebook for more information about the permitting process.

Permitting Step 1

Prepare your application

Once your ADU plans are finalized, you and your designer or contractor will submit your application package for approval. Your team will lead the process to prepare an application package. Requirements vary by County, but applications typically include:

  • Site plan (depicting existing and proposed structures)
  • Building/architectural plans (floor plans, elevation plans, and details)
  • Structural plans (foundation plan, framing plans, and associated details)
  • Other items (Title 24 energy calculations, deed restriction, address assignment form, or other materials required by your location)

See your County ADU Development Checklist and Guidebook and contact local staff to learn about your specific application process and requirements.

Permitting Step 2

submit your application

Submitting an application is different in each County. Some have online portals, and others ask that paper copies be submitted in-person. Some fees may be due when submitting your application, and some may be due later. Check your County Guidebook and County ADU Rules for more details.

After your application is submitted, the first step will be for the County to review it for completeness. They will confirm your application is complete (meaning you correctly submitted all required materials and details) and then other departments and agencies will begin their review. 

permitting Step 3

Revise your application

Staff will complete their review and provide any comments within 60 days, and often sooner. Most likely, this review will happen at a staff level (no hearings), but in less common instances, an additional permit or public hearing may be required.

If modifications to your plan are required, your team will revise and resubmit the application. Under state law, agencies/departments reviewing your plans must provide a full set of comments with a list of incorrect items and how those can be fixed.

Permitting Step 4

receive permits

After your application is approved, staff will let you know that your permit is ready and how you can receive it. Once you have paid any remaining fees and you have your permit, you can begin construction. Permits generally must be displayed at the site. They are usually valid for 180 days and often renew automatically as long as construction is ongoing and inspections are occurring.

permitting fees

ADUs can be charged a variety of fees from the County, the State, and other agencies. Some fees are based on the details of the project while others are fixed. Many of the most expensive fees, like school and water fees, are assessed by other agencies and depend on the size or location of your ADU.

The fees listed below are often required, but the exact list of fees and when they are due will vary by county. See your County Guidebook and/or contact staff for more information. Fees may include:

  • Planning permit fees
  • Plan check fees
  • Building permit fees (generally due when your permit is issued)
  • Other department fees (staff will let you know what applies to your project)
  • School District fees (often only applies to ADUs over 500 SF)
  • Development impact fees (for things like roads and sidewalks)
  • Utility and sanitation (contact utility agencies as you develop the design for your ADU for more information)

Estimating Fees: The total amount of fees depends on your property and plans. Staff may be able to provide an estimate once you have a good idea of your project details. Your County ADU Calculator can provide an estimate of fees for your project. See the County ADU Rules and your County Guidebook for fee information and examples. The total amount of fees depends on your property and plans.


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