ADU rules in Altadena, CA — also called accessory dwelling unit regulations or granny flat ordinances — cover setbacks, owner-occupancy, parking, and permit requirements.
Altadena 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 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 within the primary single-family dwelling. Altadena's hillside neighborhoods adjacent to the Angeles National Forest and Eaton Canyon are in LA County's Very High Fire Hazard Severity Zone, so ADUs must meet Chapter 7A wildland-urban interface ignition-resistant construction standards and LA County Fire Code §325 brush-clearance rules. Hillside-grading provisions of Title 22 also apply on slopes steeper than 10%. 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 Altadena 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 carry separate fire-code citations.
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Side-by-side rule comparisons with other cities in Los Angeles County.
See how other cities in Los Angeles County handle adu rules.
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