Accessory Structures in Topanga, CA: What Residents Actually Need to Know

If you live in Topanga or are thinking about moving there, accessory structures are one of those things you probably won't think about until they affect you directly. Topanga has 2 specific rules on the books covering different aspects of accessory structures, and some of them might surprise you.

ADU Rules

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.

Key details: Governing Code: LA County Code §22.140.640. Single-Family: 1 ADU + 1 JADU per lot. Multifamily Detached: Up to 2 new + conversion ADUs. Coastal Permit: Required (Santa Monica Mtns LCP). Side/Rear Setback: 4 ft (new construction).

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.

Garage Conversions

Garage conversions to ADUs in unincorporated Topanga are governed by LA County Code Title 22 §22.140.640 and California Government Code §65852.2. No replacement parking is required when a garage is converted to an ADU, and existing setbacks are preserved. A Coastal Development Permit applies in the Santa Monica Mountains Local Coastal Program area.

Key details: Governing Code: LA County Code §22.140.640. Replacement Parking: Not required. Existing Setbacks: Grandfathered. Coastal Permit: Required in SMM LCP. Permit Required: Yes — LA County building.

Converting a Topanga garage to habitable space without a building permit and CDP (where required) is a violation of LA County Code Title 22 and the Coastal Act, subject to stop-work orders, daily fines, and removal orders from LA County Code Enforcement and the Coastal Commission.

The Bottom Line

Topanga's accessory structures rules are a mixed bag. Some areas are strict, others are relaxed, and the details matter. The best approach is to check the specific rule that applies to your situation rather than assuming Topanga is broadly strict or permissive.

Keep in mind that Topanga can amend these rules at any council meeting. For the most current version of any rule mentioned here, check the specific ordinance page, where we track updates as they happen.