Learning the Rules
- Understand the rules and regulations for your community
- Learn what you can build on your property
Before you design your ADU, you need to know what you’re allowed to build. We will help you navigate the state and local laws that apply to your property.
Learning the rules is part of the Planning phase, which typically takes 1-3 months. Most ADU projects take 12-18 months to complete, but some extend to 24 months or more.
for Learning the Rules
Frequently Asked Questions
Here are a few of the most frequently asked questions about ADU rules. See the content below and your County’s ADU Guidebook for more guidance, resources, and tips for all steps of the process.
ADUs often need separate waste treatment and your system may need to be modified. Contact your Environmental Health Department early in the process. For contact information, see the Contact page.
ADUs may require a well report and well systems may need to be upgraded. Contact your County Environmental Health Department early in the process. For contact information, see the Contact page.
In almost all cases, yes! ADUs and JADUs are allowed in all single-family and mixed-use zones. If residential buildings are allowed, ADUs are almost always allowed too (with limited exceptions for safety, traffic, and water).
Homeowners can convert legally built structures (garage, barn, art studio, etc.) into an ADU. JADUs can be converted from an attached garage (but not detached). If you demolish your garage or other enclosed structure and build an ADU in its place, the ADU can be in the same footprint if it’s the same size and height of the structure it’s replacing. You may need to provide replacement parking; check County ADU Rules, see your County Guidebook, and talk with staff for more details.
If you plan on replacing a detached garage with an ADU, demolition permits, and public notice cannot be required if you have your ADU permit (unless it is in an architecturally and historically significant district). Check with staff for other garage-related policies.
Note that garage conversion ADUs may require significant moisture barriers and other design elements in order to meet building codes.
ADUs and JADUs are allowed in all residential and mixed-use zones, with limited exceptions for safety, traffic, and water.
Homeowners can build both an ADU and JADU on their property. Multifamily properties can have multiple ADUs, depending on the type and other details of the project. Contact staff for more information if interested in building ADUs on a multifamily property.
According to state law, you can build up to an 800 square foot ADU, as long as it is not over 16 feet tall and rear and side setbacks are 4 feet or more. Otherwise, size limits depend on your property and local rules. No room behind or next to your main home? You can build it in your front yard instead.
According to state law, rules about setbacks, lot coverage, and open space requirements cannot restrict you from building an 800 square foot ADU, as long as the ADU has setbacks of at least 4 feet and is not above 16 feet tall. Front setbacks also cannot restrict you from building an 800 square foot ADU, which means an ADU can be in a front yard – but only if rear or side placement isn’t possible.
Generally, homeowners are not required to live on their property if it includes an ADU. However, the County may require JADU owners to live in the primary unit or the JADU – and this may need to be recorded in a deed restriction for the property. To confirm owner occupancy rules for your area, check County ADU Rules and talk with staff early to find out.
Generally, ADUs and JADUs cannot be rented for fewer than 30 days at a time.
To see translated Spanish FAQs, head to All FAQs.
Learning the Rules, Step-by-Step
Learning the Rules Step 1
Learn about your property
First, you’ll gather some basic information about your property – what’s your Assessor’s Parcel Number (APN)? How big is your lot and how is it zoned? Check the County ADU Rules page and use our Exercises to record some basic information on your property. Your County Guidebook describes this step in more detail.
Learning the rules Step 2
Learn what you can build
Next, you’ll need to understand what you can build on your property. Local and state laws will impact what is possible for your ADU, like its size and height and may include additional requirements about parking, fire safety, and more. See the County ADU Rules to find out what applies and download your County Guidebook for more detailed information about important ADU laws.
Wildfires are a reality throughout our region, which is why it is important to understand the risk in your area. Make sure you talk to staff and find out early if your ADU is located in a Fire Hazard Severity Zone and what that means. There may be additional design requirements or review. Use the Fire Hazard Severity Zone Tool to look up your property and identify your zone.
Learning the rules step 3
Meet with staff
One of the best things you can do is to talk to County staff early in the process about potential issues and rules that might apply.
Many jurisdictions have Planning or Building Counters where you can ask questions without an appointment, or you can call or email and ask about setting a specific meeting (for hours and contact information, see the Contact page.
This conversation should cover specifics on your lot and the size, location, and type of ADU you want to build. It should also cover additional design guidelines, parking requirements, fees, and utilities as relevant. Consult the Staff Meeting Worksheet in our interactive Exercises for a list of questions to ask and be sure to bring your County Guidebook and information you’ve already collected.
If you decide to move forward, it’s a good idea to return to talk with staff so they can review the final design and provide feedback before submitting your application. While not required, this extra step can make sure you get your permit as soon as possible.
Use our Exercises to help plan your conversation and take notes. This is also a good time to contact any utility service providers (waste, sewer, gas, electricity, etc.) to confirm requirements, timelines, and fees. For contact information see the Contact page.
If your basic project details (size, number of bedrooms) change based on this meeting, it’s a good idea to adjust your estimated project budget.