Greenlight
Guides

What are Thousand Oaks' ADU rules?

Thousand Oaks is a Ventura County city, so the City of Los Angeles rules in our other guides do not apply there. Its ADU code is Article 45 of the zoning code, rewritten in November 2024 and amended in April 2025 and April 2026, and it allows one state-mandated detached ADU of up to 800 sq ft on a lot with a house, or up to 1,000 sq ft under the city's own standards 145. The state housing department found the 2026 version still out of step with state law on five points, and the code itself says state law wins where the two conflict 21.

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

Is my address actually in the City of Thousand Oaks?

Check this first, because the Conejo Valley mixes one Ventura County city, several unincorporated county pockets and a Los Angeles County city that shares its name with a Thousand Oaks neighborhood. Newbury Park is inside the city; the county supervisor's office calls it one of the largest areas of the City of Thousand Oaks, nearly 40 percent of its land 17.

These Conejo Valley communities are unincorporated Ventura County, where the county's ADU rules apply instead 17:

Westlake is the confusing one. Two portions of the Ventura County side of Westlake were annexed into Thousand Oaks in 1968 and 1972, so when Westlake Village incorporated in 1981 the homes in Ventura County stayed part of Thousand Oaks 20. The City of Westlake Village itself is in Los Angeles County, incorporated December 11, 1981 18. A Thousand Oaks mailing address settles none of this; the city's TO24 property lookup, which the city points to for permit history, does 13.

Which rules apply, the city's or the state's?

Both, and state law controls when they disagree. Thousand Oaks keeps its ADU rules in Article 45 of its zoning code, Sections 9-4.4501 through 9-4.4512, adopted by Ordinance 1732-NS effective November 22, 2024 and amended by Ordinance 1735-NS in April 2025 and Ordinance 1747-NS effective April 10, 2026 1. The code says that if it conflicts with Government Code Sections 66310 through 66342, the state sections prevail 1.

The California Department of Housing and Community Development (HCD) reviews every local ADU ordinance. On September 23, 2025, HCD found the 2025 ordinance out of compliance on six points, among them a ban on ADUs where a recorded deed restriction prohibits structures, a 16-foot height cap on detached units next to multifamily buildings, and language that read as one ADU plus one JADU per lot instead of the three units state law allows 3. The city re-adopted the ordinance on March 10, 2026, and on June 1, 2026, HCD found five remaining problems, including a ban on exterior stairs for second-story ADUs and owner-occupancy terms in the JADU deed restriction, and gave the city until July 1, 2026 to respond 2.

HCD's handbook says that while an ordinance is noncompliant, the local agency applies state standards until it adopts a compliant one 15. As of October 2026 we could not find the city's published response, so if a planner cites one of those sections against your project, ask in writing which standard applies.

How big and how tall can an ADU be in Thousand Oaks?

The state-mandated route, Section 9-4.4511, requires the city to approve one detached new ADU of 800 sq ft or less with 4-foot side and rear setbacks and a height of 16 feet, or 18 feet within a half-mile walk of a major transit stop 4. It also covers one ADU and one JADU converted from the house or an accessory structure, with up to 150 sq ft added for an entrance 4.

The city's own standards in Section 9-4.4509 go larger:

The design standards in Section 9-4.4510 require a matching roof slope, privacy glass on windows within 10 feet of a neighbor, no rooftop decks and no roof-mounted equipment 21. For LA's sizes, see ADU types for a 6,600 sq ft lot and height limits.

My lot is on a slope with oak trees. Can I still build?

Often, but the site picks the spot. Section 9-4.4509(a) says no ADU may sit on or encroach into a natural slope steeper than 25 percent 7. In the Protected Ridgeline overlay zone, no structure, grading or removal of native vegetation is allowed within 300 feet horizontally or 100 feet vertically of a ridgeline crest, unless that would preclude the minimum two units of 800 sq ft or less, in which case the ADU goes at the lowest possible elevation 7. The same section protects oaks: no construction or grading inside a protected tree's protected zone unless the 800 sq ft minimum would be precluded, and then any tree removed is replaced on site one for one with a 36-inch box coast live oak or valley oak, or an in-lieu fee is paid under Resolution 2010-014 7.

Where the 25 percent line and a tree's protected zone fall is a question for a survey and an arborist. Our survey and protected trees guides describe LA's versions of the same two questions.

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 →

Is Thousand Oaks in a fire hazard zone, and what does that change?

Much of it, yes. Fire protection in Thousand Oaks comes from the Ventura County Fire Protection District, which serves the unincorporated county and seven cities 22. The district's board adopted the State Fire Marshal's 2025 recommended Local Responsibility Area fire hazard severity zones by Ordinance 33 on May 20, 2025, effective July 1, 2025 8. Its page links a map viewer for looking up a parcel, and it says that when a parcel contains two or more zones, the highest zone applies to the whole parcel 8. A KABC analysis of the new maps found Thousand Oaks among the Ventura County cities with the most acres of very high fire hazard 9.

For an ADU the zone affects how you build, not whether you may. Article 45 has no fire-zone restriction; its only fire clause says sprinklers are not required in the ADU unless they are required for the house, and an ADU cannot trigger sprinklers in the existing house 10. The ridgeline rule above carves out vegetation removal needed for fire clearance 7. Our fire zone guide covers the wildfire construction standards, which come from the state building code.

What about parking, renting and selling the unit?

One off-street space per ADU, which may be uncovered, tandem in the driveway or in a setback, and spaces lost when a garage is converted do not have to be replaced 11. No space is required if the ADU is within a half-mile walk of public transit, is converted from existing space, is 500 sq ft or smaller, or meets another exemption in Section 9-4.4505 11.

An ADU may be rented separately but not sold separately, and neither an ADU nor a JADU may be rented for 30 days or less 12. A JADU requires a deed restriction recorded with the Ventura County Recorder at the owner's expense 12. HCD's June 2026 letter says the owner-occupancy terms in that restriction exceed what state law allows 2, and the city's ADU page still says any property with a JADU must be owner-occupied 13. For LA's rules see owner occupancy and selling an ADU separately.

What does the city charge, and how long does it take?

The city's ADU page splits fees into three kinds: a fixed planning review fee; building plan check and permit fees, which it says have averaged $2,800 to $3,200 per unit over the past three years; and impact and utility connection fees from the city, Conejo Valley Unified School District, Thousand Oaks Police Department, Ventura County Fire Department and the Conejo Recreation and Park District 13. The city's own impact fees are water and wastewater connection fees and traffic impact fees 13.

State law exempts an ADU with 750 sq ft or less of interior livable space from impact fees, and above that the fee is charged in proportion to the primary house's square footage 15. Section 9-4.4508 adds that an ADU is not a new residential use for connection or capacity charges unless it is built with a new house 14. The park district says the exemption cut its revenue 16.

The process is a building permit reviewed ministerially, with no hearing: completeness is decided within 15 business days, approval or denial within 60 days of a complete application, and an appeal goes to the Planning Commission within 10 calendar days 14. The city keeps a gallery of pre-approved plans, and says a unit built without permits before January 1, 2020 can be legalized without impact fees unless the fix requires utility infrastructure 13. Compare LADBS plan check timelines and LAUSD school fees.

What if my address is in unincorporated Ventura County?

The county's rules apply, and they are different. The Board of Supervisors adopted a state-compliant ADU ordinance for the non-coastal unincorporated areas on June 4, 2024, effective July 3, 2024 19. The county's ADU page says a unit that meets state ADU law, and every JADU, is permitted directly with a building permit; a new detached ADU on that route can be up to 850 sq ft with 4-foot side and rear setbacks 19. Larger units go through a Zoning Clearance, which allows ADUs of up to 1,800 sq ft based on lot size 19. The county planning counter is at 805-654-2488 19. Oak Park, Casa Conejo, Lynn Ranch, Hidden Valley, Lake Sherwood and Santa Rosa Valley are on this track 17.

Quick answers

How big can a detached ADU be in Thousand Oaks?

Up to 1,000 sq ft of interior livable space under the city's standards, or 800 sq ft on the state-mandated route the city must approve 54.

Is there a minimum lot size for an ADU in Thousand Oaks?

No. State law does not allow local governments to set minimum lot sizes for ADUs 23.

Can I put an ADU on a steep part of my lot?

Not on a natural slope steeper than 25 percent; Article 45 bars an ADU from sitting on or encroaching into one 7.

Does a Thousand Oaks ADU need fire sprinklers?

Only if the main house requires them. Building the ADU cannot trigger sprinklers in the existing house 10.

Is Oak Park part of Thousand Oaks?

No. Oak Park is the county's largest unincorporated community, so Ventura County's ADU rules apply there 1719.

Sources

  1. Thousand Oaks Municipal Code, Title 9 Chapter 4 Article 45 (Accessory Dwelling Units), Secs. 9-4.4501 and 9-4.4502 with ordinance history, City of Thousand Oaks (via gocodebook.com mirror of the municipal code). Facts checked 2026-10-13
  2. Review of Thousand Oaks' Accessory Dwelling Unit (ADU) Ordinance No. 1747-NS under State ADU Law, letter of June 1, 2026, California Department of Housing and Community Development (HCD). Facts checked 2026-10-13
  3. Review of Thousand Oaks' Accessory Dwelling Unit (ADU) Ordinance No. 1735-NS under State ADU Law, letter of September 23, 2025, California Department of Housing and Community Development (HCD). Facts checked 2026-10-13
  4. Thousand Oaks Municipal Code Sec. 9-4.4511 (State-mandated ADUs), City of Thousand Oaks (via gocodebook.com mirror). Facts checked 2026-10-13
  5. Thousand Oaks Municipal Code Sec. 9-4.4509(c) and (d) (Detached accessory dwelling units; accessory structures), City of Thousand Oaks (via gocodebook.com mirror). Facts checked 2026-10-13
  6. Thousand Oaks Municipal Code Sec. 9-4.4509(b) (Conversion within or attached to primary dwelling ADUs), City of Thousand Oaks (via gocodebook.com mirror). Facts checked 2026-10-13
  7. Thousand Oaks Municipal Code Sec. 9-4.4509(a) (Limits on unit location: slopes, protected ridgelines, protected trees), City of Thousand Oaks (via gocodebook.com mirror). Facts checked 2026-10-13
  8. Fire Hazard Severity Zones (2025 LRA adoption, VCFPD Ordinance 33), Ventura County Fire Department / Ventura County Fire Protection District. Facts checked 2026-10-13
  9. What new Cal Fire maps show about fire hazards in Ventura County, KABC-TV (ABC7) Eyewitness News. Facts checked 2026-10-13
  10. Thousand Oaks Municipal Code Sec. 9-4.4507(a) (Fire sprinklers and utilities), City of Thousand Oaks (via gocodebook.com mirror). Facts checked 2026-10-13
  11. Thousand Oaks Municipal Code Sec. 9-4.4505 (Parking), City of Thousand Oaks (via gocodebook.com mirror). Facts checked 2026-10-13
  12. Thousand Oaks Municipal Code Secs. 9-4.4506 (Occupancy and conveyance) and 9-4.4512 (Junior accessory dwelling units), City of Thousand Oaks (via gocodebook.com mirror). Facts checked 2026-10-13
  13. Accessory Dwelling Units (ADU FAQs: fees, renting, pre-approved plans, unpermitted units), City of Thousand Oaks Community Development Department. Facts checked 2026-10-13
  14. Thousand Oaks Municipal Code Secs. 9-4.4503 (Applications, determinations, and appeals) and 9-4.4508 (Fees), City of Thousand Oaks (via gocodebook.com mirror). Facts checked 2026-10-13
  15. Accessory Dwelling Unit Handbook (March 2026): impact fees under 750 sq ft; noncompliant ordinances, California Department of Housing and Community Development (HCD). Facts checked 2026-10-13
  16. Quimby / Park Dedication Fees, Conejo Recreation & Park District. Facts checked 2026-10-13
  17. About District 2: Communities (Casa Conejo, Hidden Valley, Lake Sherwood, Lynn Ranch, Newbury Park, Oak Park, Santa Rosa Valley, Thousand Oaks, Westlake Village), Ventura County Supervisor Jeff Gorell, 2nd District. Facts checked 2026-10-13
  18. City of Westlake Village, Los Angeles County, California, Los Angeles Almanac. Facts checked 2026-10-13
  19. Accessory Dwelling Units (unincorporated Ventura County, Non-Coastal Zoning Ordinance), Ventura County Resource Management Agency, Planning Division. Facts checked 2026-10-13
  20. Exploring the confusion over city boundaries in the Conejo Valley (reprint of Thousand Oaks Acorn, Sept. 8, 2011), Ventura County Trails (reprinting the Thousand Oaks Acorn). Facts checked 2026-10-13
  21. Thousand Oaks Municipal Code Sec. 9-4.4510 (Objective design standards), City of Thousand Oaks (via gocodebook.com mirror). Facts checked 2026-10-13
  22. Fire Protection District, Adopted Budget FY 2023-24, Budget Unit Description, County of Ventura Auditor-Controller. Facts checked 2026-10-13
  23. Accessory Dwelling Unit Handbook (March 2026): minimum lot size, California Department of Housing and Community Development (HCD). Facts checked 2026-10-13

Keep reading

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.