ADU rules in Topanga, CA — also called accessory dwelling unit regulations or granny flat ordinances — cover setbacks, owner-occupancy, parking, and permit requirements.
Topanga 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. Detached ADUs are capped at 1,200 sq ft; multifamily-lot ADUs have no maximum size under county rules. Topanga lies within the Santa Monica Mountains Coastal Zone, so a Coastal Development Permit also applies.
LA County Code §22.140.640 implements Government Code §65852.2 and §65852.22 with ministerial, non-discretionary review for ADUs and JADUs in unincorporated areas. Single-family lots may add one ADU plus one JADU; multifamily lots may add up to two detached ADUs plus conversion ADUs (at least one, but not more than 25% of the existing unit count) created within non-livable space of the existing building. Detached ADUs are limited to 25 feet (16 feet for new detached ADUs on certain lots; multifamily-lot ADUs are capped at 20 feet). Side and rear setbacks are 4 feet for new construction; attached ADUs require no separation. JADUs are capped at 500 sq ft within the primary single-family dwelling. Because Topanga sits within the certified Santa Monica Mountains Local Coastal Program, an ADU also requires a Coastal Development Permit under Title 22 unless it meets a categorical exclusion, and hillside-grading standards may apply.
Unpermitted ADUs in unincorporated Topanga 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 or removal. Coastal Zone work without a CDP carries additional Coastal Commission penalties.
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