Phase Two
Learning the Rules
- Understand the rules and regulations for your community
- Learn what you can build on your property
Timeline
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.
What if I have a building code violation or unpermitted structure on my property?
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.
What if I have an unpermitted ADU?
An unpermitted ADU can make it difficult to sell or refinance your property. If an unpermitted unit is discovered and is under construction, the county will issue a stop work order. If the building is complete, it will need an as-built permit, which has extra fees and requires substantial physical work on the building to assess the condition and details.
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.
Can I eventually sell my ADU separately from the main building?
JADUs: You’ll need to record in a deed restriction for the property that the JADU cannot be sold separately from the primary home.
ADUs: New state laws will allow for the separate sale of a detached ADU.
Will my ADU need new utility connections?
Conversion ADUs: New connections and fees not required.
Attached/detached ADUs: Separate utility connections and connection fee/capacity charges are required for new ADUs and are due when building permit is issued.
Will I need to add parking?
Parking is much less of a concern than it used to be.
One off-street parking space is required per unit, unless:
- JADU
- Within ½ mile to public transit
- In an architecturally or historically significant district
- Replacement parking for a garage demolition or conversion
- On-street parking permits are required but not offered to ADU occupant
- Within 1 block of car share
- Built as part of a new home
The required space may be tandem or in the side yard/setback (ask City or County staff to verify local rules). Garage conversions do not require replacement of the lost parking space.
Can I rent my ADU as an AirBnB or other short-term rental?
No. ADUs and JADUs cannot be rented for fewer than 30 days at a time.
Do I need to live in the main house to build an ADU or JADU?
Under state law, owner occupancy is no longer required for properties with ADUs. However, JADU owners must live in either the JADU or the main home – and this will need to be recorded in a deed restriction for the property.
How large can my ADU be?
According to state law, you can build an ADU up to 800 square feet, as long as rear and side setbacks are at least 4 feet and it is not above 16 feet tall. Otherwise, size limits depend on your property. No room behind or next to your main home? You can build it in your front yard instead.
See the Learning the Rules guide for more details.
How many ADUs and/or JADUs can I build?
Homeowners can build both an ADU and JADU on their property. Multifamily properties like duplexes, triplexes and apartment buildings can have at least two detached ADUs. Talk to your City or County staff for more information if interested in building ADUs on a multifamily property.
What do I need to do if I have a septic system or well?
ADUs often need separate waste treatment, and if you have a well, you may need to provide a well report. In either case, your system may need to be upgraded. Talk to your City or County staff or your Environmental Health Department early in the process.
Questions about Special Zones
What if I’m in a high-fire severity area?
Wildfires are a reality throughout our state, which is why it is important to understand the risk in your area. If your property is in a Fire Hazard Severity Zone or Fire Protection District there may be additional requirements or reviews. Find out about your location (use this Fire Department and Protection Districts resource list) and talk to City or County staff early on to learn how where you live might impact your ADU.
State agencies have developed several resources and guidelines to help. View the Fire Severity Zone Map and plug your address into the Fire Hazard Severity Zone Tool to look up your property and identify your zone. Use the Homeowners Checklist and review the Disaster Ready Guide and Board of Forestry Code to make sure your ADU and property are fire safe.
What if I’m in a flood area?
Hazard requirements depend on property elevation and location and may factor into ADU plans. Contact City or County staff early on to see what additional requirements your team will need to include.
What if my property is in a historic district?
Properties in Historic Districts may require additional review for ADU projects and are very likely subject to design review for consistency with historic criteria. Contact City or County staff to confirm the process and submissions required for ADUs in historic districts.
Step by Step
Learn the Rules
Keep in mindUnderstanding how local and state rules apply to your project can feel like a lot at first. Remember: City or County staff are here to help. See our Contact page for more details.
Learning the Rules
Step 1
Learn about your property
First, confirm what City or County your property is in and gather some basic information about your property:
- Assessor’s Parcel Number (APN)
- Lot size
- Neighborhood zone
- Special zones: Flood zone, seismic zone, snow load, fire districts, and more.
You may also want to verify your property lines – You may think your property ends at a fence or driveway, but these may have shifted over the years. Ask City or County staff the best way to confirm this information or contact your County Assessor & Recorder’s Office for a recorded map. If still needed for your project, consider hiring a surveyor for a detailed map of your property.
Use our ADU worksheets to take notes on all the details you’ll need.
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.
Below is a summary of state laws, but these may vary based on your location and property. Please speak with City or County staff to confirm.
Almost all residential properties are allowed to add ADUs and/or JADUs. Single-family properties can build both an ADU and a JADU, and multi-family properties can usually add multiple ADUs (but no JADUs). ADUs can also be built at the same time as new housing.
Note that all ADUs and JADUs must have their own external entry. JADUs must also have an interior entrance if sharing a bathroom with the main home.
- JADU: Maximum 500 square feet
- Detached ADU: At least 850 square feet (1 bd) and 1,000 square feet (2 bd)
- Attached ADU: At least 800 square feet or up to 50% of primary home square footage
- Conversion ADU: No requirement but limited to existing size – adding up to 150 SF of new square footage is allowed if needed for ingress or egress.
- Attached and Conversion ADUs: Up to 25 feet or height allowed by underlying zoning, whichever is less
- Detached ADUs within ½ mile of public transit: Up to 8 feet plus 2 feet for roof pitch (allows for two-story ADU)
- Multifamily: Up to 18 ft (allows for two-story ADU)
- All other ADUs: 16 ft
Setbacks are the distance from your property boundary to the main home or ADU.
Attached/detached ADUs:
- New Construction: 4 feet side and rear setbacks
- Conversions: No change in existing setbacks required
Note: According to state law, you can build up to an 800 square foot ADU, as long as rear and side setbacks are at least 4 feet and it is not above 16 feet tall. No room behind or next to your main home? You can build it in your front yard instead.
Key Resources
Learning the Rules
Step 3
Meet with staff
One of the best things you can do is to talk to City or County staff early in the process about potential issues and rules that might apply.
Use our Worksheets 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. See our Contact page for more details.
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.
