ADU rules in Castaic, CA — also called accessory dwelling unit regulations or granny flat ordinances — cover setbacks, owner-occupancy, parking, and permit requirements.
Castaic is an unincorporated CDP in Los Angeles County governed by LA County Code Title 22 §22.140.640 (Accessory Dwelling Units and Junior Accessory Dwelling Units), most recently amended April 2024. Single-family lots may add one ADU plus one JADU; multifamily lots may add up to two detached new-construction ADUs plus conversion ADUs created in non-livable existing space.
LA County Code §22.140.640 implements California Government Code §65852.2 and §65852.22 with ministerial, non-discretionary review. Detached ADUs on single-family lots are capped at 1,200 sq ft and 25 feet in height; multifamily-lot detached ADUs are capped at 20 feet. Side and rear setbacks for new construction are 4 feet; attached ADUs require no separation. JADUs are capped at 500 sq ft and must be within the primary single-family dwelling. On multifamily lots, conversion ADUs may be created within an existing multifamily building's non-livable space (storage rooms, attics, basements, passageways, garages) up to 25% of the existing unit count, plus up to two detached new-construction ADUs. Castaic is partly in LA County's Very High Fire Hazard Severity Zone, so ADU construction is also subject to Chapter 7A wildland-urban interface building standards and brush-clearance requirements under LA County Fire Code §325. No parking is required where the property is within a half-mile walking distance of public transit or another state exemption applies.
Unpermitted ADUs in unincorporated Castaic are violations of LA County Code Title 22 enforced by LA County Public Works and Code Enforcement, with stop-work orders, daily-accruing fines, and required permitting. WUI-zone violations (e.g., non-ignition-resistant materials in fire-hazard zones) carry separate citations.
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