Accessory Dwelling Units

An accessory dwelling unit (ADU) is a residential unit that can be added to a lot with an existing single-family dwelling or multi-family dwellings.

The County offers a Pre-Reviewed ADU Program where Residential Single-Family customers choose from County reviewed plans, allowing a more cost-effective and streamlined process. Though these plans are free, customers will still need to hire an engineer or architect for additional site-specific items.

To apply for an ADU, complete the ADU Pre-Screening Checklist and then the Building (Construction) Permit Application process.

**The regulations outlined in the ADU Pre-Screening Checklist may impact allowed number of ADU's and site design.**

Updated Regulations

On June 3, 2025, the Board of Supervisors adopted updated regulations relating to ADUs.

Inland Area - Updated regulations take effect July 3, 2025.
Coastal Zone - Updated regulations are pending certifications by the California Coastal Commission to take effect; in the meantime, existing regulations remain in effect.

Updated regulations include:

ADU Pre-Screening Checklist (click to download pdf). An ADU application is required to include a checklist certifying the proposed project complies with regulations that may impact the allowed number of ADUs and site design.
Number of ADUs. The number of allowed ADUs per parcel increased from 2 to 3 for single-family parcels and from 2 to 8 for multi-family parcels, if compliant with public health and safety regulations. Parcels that use an urban lot split are limited to 4 total dwelling units per parcel, including single-family dwellings, urban dwellings, and ADUs.
Front Setback. Non-attached ADUs over 800 square-feet are subject to the same front setback requirements as the primary residence; no minimum front setback for ADUs 800 square-feet or below.
Guesthouse. Parcels with a single-family dwelling are allowed accessory dwellings and one guesthouse.

Last updated: June 19, 2025

FAQs

What is an Accessory Dwelling Unit (ADU)?

An attached or detached residential dwelling unit that provides complete independent living facilities for one (1) or more persons and is located on a lot with a proposed or existing primary residence. It shall include permanent provisions for living, sleeping, eating, cooking, and sanitation on the same parcel as the single-family or multi-family dwelling is or will be situated.

An ADU also includes the following:

An efficiency unit.
A manufactured home, as defined in Section 18007 of the Health and Safety Code.

What land use categories (i.e. zoning) allow ADUs?

ADUs may be permitted in the following land use categories:

REC

RMF

RSF

Where are ADUs excluded?

ADUs shall not be allowed within the following areas:

Regional Water Quality Control Board Exclusion
- All areas of the County where the Regional Water Quality Control Board has issued a notice of resource constraints through moratoria or other means.
Within the Cambria Community Services District boundary
Within the Los Osos Groundwater Basin boundary and/or within the Los Osos Groundwater Basin Plan Area.

Click here to view excluded areas on a map

Where is the Coastal Zone and Inland Area?

Click here to view Coastal Zone and Inland Area on a map

Does the Coastal Zone require noticing to Coastal Commission?

Yes. All ADUs in the Coastal Zone require additional noticing.

If the proposed ADU is in the Coastal Appealable Zone, it may be appealed to the Coastal Commission. Please check with County Planning Staff to determine if the parcel is appealable to the Coastal Commission.

Contact Us

Does an ADU need a water will-serve letter or well test?

COMMUNITY WATER

A will-serve letter from the water purveyor will be required. Note: Some water purveyors, such as Cambria CSD, may not be issuing any new water connections. Please contact the water purveyor directly for more information.

ONSITE WELL

A well test in compliance with Section 19.07.040(b) will be required.

Does an ADU need a wastewater will-serve letter or it's own septic system?

SITES SERVED BY COMMUNITY SEWER

A will-serve letter from the wastewater service provider will be required. Note: Some wastewater service providers, such as Cambria CSD, may not be issuing any new wastewater connections. Please contact the wastewater service provider directly for more information.

SITE SERVED BY ONSITE WASTEWATER TREATMENT SYSTEMS

Sites served by onsite wastewater treatment systems (such as septic systems) will have to satisfy the requirements of the Building Code (Title 19), which may include standards for lot size. For sites served by onsite wastewater treatment systems, such as septic systems, please contact planning staff to determine if those requirements, which may include lot size standards, can be satisfied.

Phone: (805) 781-5600

Email: [email protected]

Will fire sprinklers be required for an ADU?

Fire sprinklers shall be required for attached ADUs if the primary dwelling requires fire sprinklers or if two or more ADUs (including junior ADUs) are attached to the primary dwelling.

Are ADUs allowed on Williamson Act contracted properties?

Yes, as allowed by the County Land Use Ordinance. ADUs in the Coastal Zone shall not be located on prime agricultural soils unless there is no other building site on the ownership that is all of the following:

a. On other than prime soils;
b. Less than 20 percent in slope;
c. Not within a designated Flood Hazard Combining Designation.