Accessory Dwelling Units & Junior Accessory Dwelling Units
Accessory Dwelling Units (ADUs) and Junior Accessory Dwelling Units (JADUs) are inexpensive ways to create smaller, more affordable rental housing units that may provide revenue streams for property owners while increasing the availability of rental housing in the county. ADUs and JADUs are established secondary to an existing or proposed single-family or multi-family primary dwelling. See Standards for ADUs and JDUs for additional information.
Changes to the County's inland code for ADUs and JADUs took effect January 8, 2026
Amendments to County Zoning Code (Chapter 26) pertaining to ADUs and JADUs were approved by the Sonoma County Board of Supervisors on December 9, 2025, with Ordinance No. 6544 (PDF) and took effect January 8, 2026.
Updates include the following:
- Existing unpermitted ADUs and JADUs created before January 1, 2020, may now be permitted unless in substandard condition. Learn more.
- More flexibility on the types of ADUs allowed on lot.
- Changes to standards applied to ADUs for compliance with State ADU Law.
- Relocation and consolidation of standards to Sections 26-24-202 (ADUs) and 26-24-190 (JADUs).
- Owner occupancy is no longer required for JADUs with independent sanitation facilities.
What are ADUs and JADUs?
Accessory Dwelling Units (ADUs) are also known as granny units, in-law units, second units, and backyard cottages. An ADU is a small dwelling unit that may be established in addition to single-family or multifamily dwellings in zones where these primary dwellings are allowed.
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- Detached: A new construction unit separate from the primary dwelling. May use eligible ADU Ready pre-reviewed plans.
- Attached: A newly constructed unit connected to a primary dwelling or another accessory structure.
- Conversion: A unit created entirely within an existing primary dwelling or accessory structure.
- Combination: A partially converted unit attached to an existing structure with newly constructed elements.
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- The quantity, type, and size of ADUs allowed on a lot depends on existing structures, zoning, and site constraints. See Standards for ADUs and JADUIs for additional information.
- ADUs can be rented for long-term occupancy (30-days or longer), but they cannot be used as short-term rentals.
A Junior Accessory Dwelling Unit (JADU) is a specific type of ADU converted from space within a single-family dwelling that is no larger than 500 square feet. A JADU may have separate sanitation facilities or share them with the primary dwelling.
ADUs vs. JADUs vs. Guesthouse
Sonoma County allows several types of residential accessory structures (see Policy 1-4-6, Residential Accessory Structures for a complete list). Below is a summary of the differences among a few of the most common residential accessory structures: Accessory Dwelling Units (ADUs), Junior Accessory Dwelling Units (JADUs), and guest houses.
| Structure Type | Accessory Dwelling Unit | Junior Accessory Dwelling Unit | Guest House |
|---|---|---|---|
| Structure | May be attached to or detached from the main dwelling or accessory structure | Must be created from, and within the footprint of, an existing or proposed single-family dwelling | Accessory building to a single-family dwelling which consists of a detached living area of a permanent type of construction |
| Kitchen | Must have a full kitchen (see Policy 1-4-5, Definition of a Kitchen) | Must have an efficiency kitchen | Cannot have a kitchen or wet bar |
| Bathroom | Must have a full bathroom | Must have direct access to a bathroom, either inside the unit or in the main house | May have a half or full bath |
| Long-Term Rental | Can be rented | Can be rented | Cannot be rented or occupied separately from the main house |
| Transient Rental | Prohibitied from use as a vacation rental or other transient rental | Prohibited from use as a vacation rental or other transient rental | May be able to be used as part of a vacation rental or hosted rental with appropriate permits and licensing |
| Z Combining District | Prohibited in the Z Combining District | Allowed in the Z Combining District | Allowed in the Z Combining District |
| Size Limit | Varies - see Standards for ADUs and JADUs | 500 square feet | 640 square feet |
| Minimum Permit Required | Building permit* | Building permit* | Building permit* |
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Zoning Code Reference |
Section 26-24-020 of the Sonoma County Municipal Code. |
Section 26-24-190 of the Sonoma County Municipal Code. | Section 26-24-170 of the Sonoma County Municipal Code. |
*Additional construction-related permits such as for grading, wells, or setic systems may be required to support a new ADU or JADU (see Standards for ADUs and JADUs), ADUs in the Coastal Zone generally require additional land use and coastal development permits.
Benefits of ADUs
Accessory dwelling units offer a host of benefits to owners, occupants, and the community.
Rental Income
Not only are ADUs relatively affordable to construct, but they can provide a source of income for homeowners. The ADU Center provides resources for estimating potential rental income and return on investment.
Increasing Housing Stock
Housing needs well exceed housing supply in California. ADUs add subtle yet valuable density to established areas that may not accommodate larger developments. ADUs may also be used to cater to people at a variety of income levels and can provide as much living space as many newly built apartments and condominiums. They are well suited for couples, small families, friends, young people, disabled people, and seniors.
Familial and Multigenerational Housing
ADUs allow extended families to live near one another while maintaining privacy and individual spaces. ADUs give homeowners the flexibility to share independent living areas with family members, friends, and others. Among many scenarios, this can mean providing seniors an accessible place to age as they require more care or allowing family members with certain disabilities to obtain a sense of independence while being close at hand.
Safety and Security
Because ADUs are often occupied by family or friends of the property owner, they can provide additional sets of trustworthy eyes and ears for the neighborhood. This can be especially appealing for homeowners who are concerned about their safety or the security of their property. Having additional people on a parcel may also mean more hands available to respond to crises such as fire or medical emergencies.
Environmental Benefits
ADUs are generally smaller in size, located on already-developed lots, rely on existing systems for utilities, and are relatively easy to construct for water and energy efficiency compared to a typical single-family home. ADUs are considered a sustainable way of increasing housing stock since they do not require outward urban expansion, take fewer materials to construct, and can help reduce per-housing unit urban impacts. For example, with the addition of an ADU, the same quantity of resource usage and pollutants commonly associated with landscape maintenance may cover the landscaping needs for two homes instead of one.
Want to Build an ADU? Let's get started.
The exact process and requirements for obtaining an ADU depend on the parcel's location. Check our Zoning and Land Use Map Viewer to determine whether your parcel is inland or in the coastal zone.
Inland ADUs.
- Be sure to review Standards for ADUs and JADUs to determine whether an ADU or JADU is allowed on your lot and what standards and permit requirements may apply.
- Building an ADU or JADU provides a step-by-step process for creating ADUs and JADUs on parcels outside the coastal zone (parcels without CC zoning).
Coastal ADUs.
- ADUs in the coastal zone (parcels with CC zoning) have different standards than those outside the coastal zone. While the general six-step process remains the same, the requirements for each step differ. See Coastal Zone ADUs for more information.
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