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What are the ADU rules in unincorporated LA County, and do they apply to me?

It depends on where the parcel sits, not on what the mailing address says. The County itself warns that residents of unincorporated areas are often unsure which jurisdiction they are in because their mail lists a neighboring city 1. If the lot is outside every city, the local rules come from County Code Title 22, section 22.140.640, which the Board of Supervisors last amended on July 29, 2025 12; LA County Planning reviews the ADU and County Public Works Building and Safety issues the building permit 165. State ADU law sets the floor on both sides of the line, because it applies to every city and county 7.

Edited by Ryan Rambo, construction managerFacts checked 2026-10-13

Is my house in the City of Los Angeles or in unincorporated LA County?

Check the parcel, not the envelope. The County says residents of unincorporated areas are often unsure which jurisdiction they belong to because their mailing address lists an adjacent city 1. Unincorporated land covers more than 2,600 square miles, two-thirds of the County's area and one-tenth of its population 2.

Three free lookups settle it:

  1. LA County Jurisdiction Lookup on planning.lacounty.gov says whether the address is unincorporated and whether LA County Planning is your planning department 1.
  2. Z-NET, the County zoning map, covers every area outside a city; anything masked out in white is inside one of the 88 cities 3.
  3. ZIMAS, the City of Los Angeles map, shows a parcel's zoning and permit history when it is in the City 4.

Public Works adds the EPIC-LA Permit Helper, where you type an address and see the permits that apply there 6.

The County's San Fernando Valley Planning Area includes the unincorporated communities of Kagel and Lopez Canyons, Sylmar Island, Oat Mountain, West Chatsworth, Westhills and Universal City 19. A Sylmar, Chatsworth or Canoga Park mailing address can belong to any of them.

Who makes the ADU rules once I know I am in the County?

Two layers, same as in the City. State ADU law applies to every local agency, defined as a city, county, or city and county 7; that is why the 800 sq ft detached unit and the 60-day clock exist on both sides of the line 2523. The local layer in unincorporated territory is County Code Title 22, section 22.140.640, last amended by the Board of Supervisors on July 29, 2025 and effective August 28, 2025 12.

Two County departments handle an ADU. LA County Planning reviews the plans first: you file a Regional Planning Base Application through EPIC-LA, and after you pay the fee the ADU is approved or denied within 60 days 16. Public Works Building and Safety issues the building permit; if your property is in unincorporated LA County you work with LA County Public Works, which runs 10 district offices for unincorporated communities 5.

The County ordinance is still under state review. On December 1, 2025, the state housing department (HCD) found that Ordinance No. 2025-0029 fails to comply with state ADU law in several respects, including allowing two detached ADUs on a multifamily lot where state law requires up to eight 13. A 2026 amendment is posted as a draft, but as of October 2026 the County says hearings have not been scheduled, the draft does not carry the force of law, and existing County and state rules govern current projects 14. Where the two disagree, ask Regional Planning in writing which it will apply to your lot.

What can I build on an unincorporated single-family lot?

Up to four accessory units, by the County's own count: a junior ADU of up to 500 sq ft inside the home, a state-exempt interior ADU, a state-exempt detached ADU of up to 800 sq ft with a 16-to-20-foot height limit and 4-foot side and rear setbacks, and a local ADU of up to 1,200 sq ft 15. The first three are the same state units you get in the City; the 1,200 sq ft unit is the County's local allowance.

County standards that differ from the City's:

The state rules the County cannot override are in our setbacks and owner-occupancy guides.

Check your own lot, free.

Put in your address and see your zoning, lot size, fire and hillside zones, sewer distance and what is already built, from the city's own records.

Get my free Lot Snapshot →

My canyon lot is in a fire zone. Does the County treat that differently than the City does?

Yes, and the difference is road access. Where any part of a lot is in a Very High Fire Hazard Severity Zone and a Hillside Management Area, the County prohibits an ADU or JADU unless the lot has two distinct means of vehicular access to a highway, except for the state-exempt units in its Subsection H 9. The 2025 amendment added that exception to match state law: statewide-exemption ADUs and JADUs are allowed on fire-zone lots regardless of vehicular access 30.

In practice, a Kagel Canyon lot on a single dead-end road can still get an 800 sq ft detached state ADU, a garage conversion or a JADU, but the County's 1,200 sq ft local ADU may be off the table. The County describes Kagel Canyon as a Very High Fire Hazard Severity Zone with limited access points 20.

Inside the zone the ordinance also requires parking for the ADU unless an exception applies, such as a unit with no bedroom or a detached unit of up to 800 sq ft and 16 feet on a single-family lot 10.

The City's own fire zone, Hillside Ordinance and 150-foot fire access rules do not apply on County land.

What about the Santa Monica Mountains, Universal City and Sylmar Island?

Each is a different case.

Santa Monica Mountains. The unincorporated part of the range west of the City of Los Angeles and outside Malibu is the Santa Monica Mountains Coastal Zone, about five miles deep and 81 square miles 21. There the County ordinance steps aside: in a Coastal Zone, ADUs and JADUs follow the applicable Local Coastal Program 8, and the County issues the coastal permits for most new development 21. State ADU law still applies but does not lessen the Coastal Act's resource protection policies 22. North of the coastal zone the ordinance prohibits local ADUs on lots between Old Topanga Canyon Road, the coastal zone boundary, Calabasas and the City of Los Angeles, and on Santa Monica Mountains North Area lots whose only access is Lobo Canyon Road or Triunfo Canyon Road, with the state-exempt units excepted 11.

Universal City. Unincorporated, but governed by an approved specific plan 19, and described by the County as entirely surrounded by incorporated cities, with City of Los Angeles homes on its east side 20. A house with a Universal City address is almost certainly in the City; the County island is the studio.

Sylmar Island. An unincorporated foothill strip that the County describes as mostly undeveloped, with one residential home 20. Nearly every Sylmar house is in the City; our Sylmar guide covers those.

How does the County permit process actually run?

Planning first, then building, with other County agencies signing off along the way.

  1. Confirm jurisdiction. The County's step-by-step guide starts with Z-NET: type in your address or Assessor's Parcel Number 316.
  2. Regional Planning approval. Submit a Regional Planning Base Application through EPIC-LA with a land use application, plans and photos; after you pay the fee the ADU is approved or denied within 60 days 16.
  3. Agency referrals. The plan check engineer lists the County, state or federal agencies whose approval you need before the permit issues 17.
  4. Septic. Many canyon lots are not on sewer. Since June 16, 2025, County Public Health counts an ADU or JADU as additional bedrooms on the existing onsite wastewater system rather than a separate unit, so the 2.5-acre density rule no longer applies, but a system evaluation is required if the system has been in use for over 15 years 18.
  5. Building permit. File it through EPIC-LA or at a district office with the approved Planning set, structural plans if needed and Title 24 energy calculations 16.

The County also offers free pre-approved plans, approved by both Regional Planning and Public Works: Plan A at 1,200 sq ft with three bedrooms, Plan B at 1,200 sq ft with two, and Plan C at 800 sq ft with one, each still needing a site-specific plot plan 17. The City's version is in our standard plans guide.

Quick answers

Does state ADU law apply in unincorporated LA County?

Yes. State ADU law applies to every local agency, defined as a city, county, or city and county, whether general law or chartered 7.

How long does the County have to decide on my ADU?

Regional Planning says 60 days from payment of the application fee 16. Under state law a completed application is deemed approved if the local agency has not acted within 60 days 23.

Can I legalize an ADU that was built before 2020 on County land?

Public Works has a process under AB 2533 for an unpermitted ADU or JADU built before January 1, 2020, with corrections limited to health and life-safety items rather than full current code 24.

My lot is on septic. Can I still add an ADU?

Possibly. Since June 2025 County Public Health treats an ADU or JADU as additional bedrooms on the existing septic system, and requires a system evaluation if it has been in use for over 15 years 18.

Does the County have pre-approved ADU plans?

Yes. Plans A and B are 1,200 sq ft and Plan C is 800 sq ft, pre-approved by both Regional Planning and Public Works Building and Safety, and each needs a site-specific plot plan 17.

Sources

  1. Unincorporated Los Angeles County: Are we your planning department?, LA County Planning (Department of Regional Planning). Facts checked 2026-10-13
  2. Unincorporated Los Angeles County: size and population, LA County Planning (Department of Regional Planning). Facts checked 2026-10-13
  3. Find My Zoning (Z-NET), LA County Planning (Department of Regional Planning). Facts checked 2026-10-13
  4. Zoning Search (ZIMAS), Los Angeles City Planning. Facts checked 2026-10-13
  5. Building and Safety: who assigns the address, district offices and EPIC-LA, LA County Public Works. Facts checked 2026-10-13
  6. EPIC LA Permit Helper, LA County Public Works. Facts checked 2026-10-13
  7. Accessory Dwelling Unit Handbook (March 2026): Are charter cities and counties subject to the new ADU laws?, California Department of Housing and Community Development (HCD). Facts checked 2026-10-13
  8. Ordinance No. 2025-0029 amending Title 11 and Title 22 of the County Code (ADUs and JADUs), transmitted by County Counsel for adoption July 29, 2025, Section 22.140.640 B (Applicability), County of Los Angeles Board of Supervisors / County Counsel. Facts checked 2026-10-13
  9. Ordinance No. 2025-0029 amending Title 11 and Title 22 of the County Code (ADUs and JADUs), transmitted by County Counsel for adoption July 29, 2025, Section 22.140.640 C.2 (Very High Fire Hazard Severity Zone), County of Los Angeles Board of Supervisors / County Counsel. Facts checked 2026-10-13
  10. Ordinance No. 2025-0029 amending Title 11 and Title 22 of the County Code (ADUs and JADUs), transmitted by County Counsel for adoption July 29, 2025, Section 22.140.640 G.1.d (Parking), County of Los Angeles Board of Supervisors / County Counsel. Facts checked 2026-10-13
  11. Ordinance No. 2025-0029 amending Title 11 and Title 22 of the County Code (ADUs and JADUs), transmitted by County Counsel for adoption July 29, 2025, Section 22.140.640 C.1 (Prohibited Areas), County of Los Angeles Board of Supervisors / County Counsel. Facts checked 2026-10-13
  12. Informational Memo: ADU Ordinance Amendment (Aug. 21, 2025): adoption and effective dates, LA County Planning (Department of Regional Planning). Facts checked 2026-10-13
  13. Review of Los Angeles County's Accessory Dwelling Unit (ADU) Ordinance under State ADU Law (letter of Dec. 1, 2025), California Department of Housing and Community Development (HCD). Facts checked 2026-10-13
  14. 2026 ADU Ordinance Amendment (project page, updated July 2026), LA County Planning (Department of Regional Planning). Facts checked 2026-10-13
  15. 2026 ADU Ordinance Amendment: Single-Family Home Guide (May 4, 2026), LA County Planning (Department of Regional Planning). Facts checked 2026-10-13
  16. Step-by-Step Guide for Accessory Dwelling Units (ADUs) in the County of Los Angeles Unincorporated Areas (1/23/23), LA County Public Works, Building and Safety / LA County Planning. Facts checked 2026-10-13
  17. Pre-Approved ADU Standard Plans Program, LA County Public Works, Building and Safety. Facts checked 2026-10-13
  18. Updated requirements for Accessory Dwelling Units (ADUs) and Junior Accessory Dwelling Units (JADUs) on onsite wastewater treatment systems (June 16, 2025), LA County Department of Public Health, Environmental Health Division. Facts checked 2026-10-13
  19. San Fernando Valley Area Plan: Notice of Preparation of a Program EIR (April 2026), LA County Planning (Department of Regional Planning). Facts checked 2026-10-13
  20. San Fernando Valley Area Plan, Public Review Draft (Feb. 19, 2026): Kagel and Lopez Canyons, Sylmar Island and Universal City, LA County Planning (Department of Regional Planning). Facts checked 2026-10-13
  21. Santa Monica Mountains Local Coastal Program: What is the Santa Monica Mountains Coastal Zone?, LA County Planning (Department of Regional Planning). Facts checked 2026-10-13
  22. Accessory Dwelling Unit Handbook (March 2026): Coastal Commission, California Department of Housing and Community Development (HCD). Facts checked 2026-10-13
  23. Accessory Dwelling Unit Handbook (March 2026): Summary of Recent Changes, California Department of Housing and Community Development (HCD). Facts checked 2026-10-13
  24. Legalizing Unpermitted ADUs & JADUs Handout (AB2533), Feb. 19, 2026, LA County Public Works, Building and Safety. Facts checked 2026-10-13
  25. Accessory Dwelling Unit Handbook (March 2026), 66323 Units: Single-Family Detached ADUs, California Department of Housing and Community Development (HCD). Facts checked 2026-10-13
  26. Ordinance No. 2025-0029 amending Title 11 and Title 22 of the County Code (ADUs and JADUs), transmitted by County Counsel for adoption July 29, 2025, Section 22.140.640 G.1.b (Height), County of Los Angeles Board of Supervisors / County Counsel. Facts checked 2026-10-13
  27. Ordinance No. 2025-0029 amending Title 11 and Title 22 of the County Code (ADUs and JADUs), transmitted by County Counsel for adoption July 29, 2025, Section 22.140.640 G.1.e (Distance from Publicly Dedicated Open Space), County of Los Angeles Board of Supervisors / County Counsel. Facts checked 2026-10-13
  28. Informational Memo: ADU Ordinance Amendment (Aug. 21, 2025): proximity to animal keeping, LA County Planning (Department of Regional Planning). Facts checked 2026-10-13
  29. Informational Memo: ADU Ordinance Amendment (Aug. 21, 2025): residential design standards, LA County Planning (Department of Regional Planning). Facts checked 2026-10-13
  30. Informational Memo: ADU Ordinance Amendment (Aug. 21, 2025): high fire risk areas, LA County Planning (Department of Regional Planning). Facts checked 2026-10-13

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Greenlight is not a contractor, architect or engineer, and this is not legal advice. Rules change; every fact here shows the date we last checked it.