ADU rules in San Luis Obispo County, CA — also called accessory dwelling unit regulations or granny flat ordinances — cover setbacks, owner-occupancy, parking, and permit requirements.
SLO County Code Section 22.30.470 (Inland) and corresponding Title 23 provisions allow up to 3 ADUs per single-family parcel and up to 8 per multifamily parcel under Ordinance 3536 (adopted June 2025, effective July 3, 2025). Applications must be approved or denied within 60 days, or 30 days for County-authorized pre-reviewed plans.
On June 3, 2025, the SLO County Board of Supervisors adopted Ordinance 3536, updating ADU regulations in Title 22 (Inland Land Use Ordinance) and corresponding Title 23 coastal provisions. The number of allowed ADUs per parcel increased from 2 to 3 for single-family parcels, and from 2 to 8 for multifamily parcels (subject to health and safety compliance). Detached ADUs over 800 sq ft must meet the same front setback as the primary residence; ADUs 800 sq ft or smaller have no minimum front setback. Land use applications for ADUs must be approved or denied within 60 days of completeness (30 days if using County-authorized Pre-Reviewed ADU plans). One guesthouse is allowed alongside accessory dwellings on single-family parcels. ADUs are prohibited in specific service-constrained areas including the Cambria Community Services District and the Los Osos Groundwater Basin boundary due to water supply limitations.
Building an ADU without permits is a code enforcement violation under Title 22, subject to stop-work orders, after-the-fact permit fees, and potential demolition orders. Operating an unpermitted ADU as a rental adds additional code violations.
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