Yolo County, CA Accessory Structures: ADU Rules (2026)
ADU rules in Yolo County, CA, also called accessory dwelling unit regulations or granny flat ordinances, cover setbacks, owner-occupancy, parking, and permit requirements.
Key Facts
- Detached ADU max size
- 1,200 sq ft floor area (Sec. 8-2.506)
- Attached ADU max size
- 50% of primary residence living area
- New-construction setbacks
- 4 ft side and rear (Sec. 8-2.506(b)(3)(ii))
- Conversion setbacks
- None required for converted existing structures
- Parking requirement
- 1 space per ADU; waived near transit, historic districts, or interior conversions
- Owner-occupancy
- Prohibited under state law (Gov. Code Sec. 66315)
- Impact-fee exemption
- ADUs at or below 750 sq ft are exempt (Gov. Code Sec. 66311.5)
- Permit decision deadline
- 60 days, or deemed approved (Gov. Code Sec. 66317)
- Local ordinance status
- HCD found 2022 ordinance noncompliant on Dec. 5, 2025; state ADU Law applies directly
Summary
ADUs are a ministerial, permitted use on residentially zoned lots, with a 1,200 sq ft cap on detached units and 4-foot side/rear setbacks for new construction; state ADU Law preempts most local standards.
(1) Accessory dwelling units (ADU) in residential zones are a permitted use only subject to the requirements set forth separately below and in no case shall an ADU that meets the minimum requirements be subject to discretionary review. A ministerial permit for an ADU may be disapproved only if the Planning Director finds that the ADU would be detrimental to the public health and safety or would introduce unreasonable privacy impacts to the immediate neighbors. A building permit application for an ADU shall be approved or disapproved within 120 days of receipt. (2) The maximum height of an ADU within a required setback shall be 16 feet. (3) The following setback requirements for ADUs shall apply: (i) Setbacks for existing structures or conversion of structures. No setback shall be required for an existing living area or accessory structure or a structure constructed in the same location and to the same dimensions as an existing structure that is converted to an accessory dwelling unit or a portion of an accessory dwelling unit. (ii) New construction. Newly constructed ADUs that do not result from the conversion of an existing structure shall require a setback of four feet from the side and rear property lines. (iii) Building separation. Detached accessory structures subject to a Building Permit shall be separated from principal structures by a minimum of ten (10) feet and from other detached accessory structures subject to a Building Permit by a minimum distance specified by applicable building or fire codes. (4) The following parking standards shall be required of all accessory housing structures except as noted for an ADU: (i) One parking space shall be provided per accessory dwelling unit. Parking for an ADU may be provided as tandem parking on an existing driveway. Parking lost through the conversion of a garage, carport, or covered parking structure is not required to be replaced. Additional parking for an ADU is not required if the ADU is located: 1. within one-half mile walking distance of public transit; 2. within an architecturally and historically significant historic district; 3. within an existing primary residence or an existing accessory structure; when on-street parking permits are required but not offered to the occupant of the accessory dwelling unit; or 4. when there is a car share vehicle located within one block of the accessory dwelling unit.
Full Breakdown
506(b) treats accessory dwelling units (ADUs) in residential zones as a permitted, ministerial use, with no discretionary review for an ADU that meets the minimum requirements. A detached ADU may not exceed 1,200 square feet in floor area, and an ADU attached to the primary residence may not exceed 50 percent of the existing living area. Newly constructed ADUs not converted from an existing structure require a 4-foot side and rear setback; ADUs created within an existing structure or rebuilt in the same footprint require no setback.
506(b)(4)). 507. Importantly, the California Department of Housing and Community Development (HCD) sent Yolo County a Letter of Technical Assistance dated December 5, 2025 stating that the County's 2022 ADU ordinance is outdated and out of compliance with State ADU Law; under Government Code Section 66316, a noncompliant local ADU ordinance is 'null and void' and the County must apply State ADU Law directly until a compliant ordinance is adopted. Under current state law (Gov. Code Sections 66310-66342), ADUs up to 850 sq ft (or 1,000 sq ft with more than one bedroom) must be approved, impact fees are prohibited on ADUs at or below 750 sq ft, owner-occupancy may not be required, and applications must be approved or denied within 60 days.
Violations & Fines
Building an ADU without a permit is a Title 8 zoning violation enforceable by Yolo County Code Enforcement. State law (Gov. Code Section 66332) bars the County from denying a permit for an unpermitted ADU built before January 1, 2020 for building-code violations unless the violation makes the building substandard, and Section 66331 lets owners apply for a five-year enforcement delay to bring a substandard ADU into compliance when no health-and-safety threat exists.
Frequently Asked Questions
Do I need a use permit to build an ADU in unincorporated Yolo County?
How big can my detached ADU be?
Does Yolo County require off-street parking for my ADU?
Can the County require me to live in the primary house if I rent the ADU?
Is Yolo County's ADU ordinance current?
Sources & Official References
Other rules in Yolo County
How Yolo County compares: Easiest Cities to Build an ADU·California rules heatmap·Compare Yolo County to another location·View the California accessory structures overview
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