Building an ADU in Thousand Oaks

Which rules apply in Thousand Oaks

The city's ADU standards are in Thousand Oaks Municipal Code Title 9, Chapter 4, Article 45, which the city's ADU application tells you to review. The code is published on American Legal. The city has amended Article 45 twice recently: Ordinance No. 1735-NS, adopted April 25, 2025, and Ordinance No. 1747-NS, adopted March 10, 2026. The text of Ordinance No. 1747-NS presented to the City Council for adoption says it takes effect on the 31st day after adoption, and that where it conflicts with the state's ADU law, state law prevails.

HCD reviewed both. Its June 1, 2026 letter on Ordinance No. 1747-NS says the ordinance "fails to comply with State ADU Laws" and gave the city until July 1, 2026 to respond with a plan to amend it or adopt findings. The next section lists what HCD flagged.

State law generally overrides a stricter local rule. Where this page says "the city says X; state law says Y," plan around state law and confirm with the Planning Division at (805) 449-2323 before you design. [1][2][3][7]

What HCD told Thousand Oaks in 2025 and 2026

June 2026 (Ordinance No. 1747-NS). HCD's findings:

• Unit count. The ordinance counts the one ADU built under local standards against the state's by-right allowances. HCD said the city must allow the full set of state by-right units and at least one ADU under its local standards.
• Zones. The ordinance limits single-family ADUs to lots in the R-A, R-E, R-O, R-1, RPD and HPD zones (or a specific plan) with one main home. HCD said that would block ADUs on lots with nonconforming conditions, such as two houses on one lot, and told the city to allow all single-family options in all residential zones and all ADU options in multifamily zones.
• Outside stairs. The ordinance says "Exterior stairs are not permitted." HCD said this can make an ADU that meets the state's 25-foot attached height infeasible and told the city to remove it.
• JADU deed restriction. The ordinance's JADU deed restriction includes the owner-occupancy rule. HCD said the deed restriction may contain only the ban on separate sale and the JADU's size and features.

September 2025 (Ordinance No. 1735-NS). The earlier letter said, among other things, that the city confirmed it allowed only one ADU (converted or detached) plus a JADU on a single-family lot, while state law allows a converted ADU, a new detached ADU and a JADU together; that the ordinance barred ADUs where a recorded deed restriction prohibits structures; that it allowed newly built JADUs outside the walls of the house; and that its height limits for ADUs on multifamily lots were too low.

These letters describe the ordinances HCD reviewed. Ask Planning whether the city has changed its rules since. [3][7]

Size, height and setbacks

Ordinance No. 1747-NS and the city's ADU application set these limits:

• Detached ADU: up to 1,000 sq ft of interior living space. Height 16 feet, or 18 feet on a lot with a single-family home within a half-mile walk of a major transit stop or high-quality transit corridor; the ordinance allows 2 more feet to match the house's roof pitch. Setbacks are 4 feet from side and rear lot lines, the house's front setback, and 6 feet from other buildings, wall to wall.
• Attached or converted ADU: up to 850 sq ft or 50% of the house's floor area, whichever is greater. Height 25 feet, or the height limit that applies to the house in section 9-4.2501, whichever is lower. New space needs 4-foot side and rear setbacks and the house's front setback, and the ADU must share at least 10 feet of wall with the house, with no inside connection.
• Conversions: part of a legal house or all or part of an accessory structure can become an ADU even if it doesn't meet the height and setback rules, and an accessory structure can be torn down and rebuilt in the same place and size. You can add up to 150 sq ft for entry and exit.
• JADU: no taller than the existing structure it is in.
• Where you can't build: the ordinance bars ADUs on natural slopes steeper than 25% and limits building near protected ridgelines and protected trees.
• Design: an attached or converted ADU must match the house's materials and colors, a new detached ADU must use at least one of the house's materials and colors, and the roof slope must match the house's main roof slope. Windows within 10 feet of a neighboring home need privacy glass, and roof decks are not allowed. For a second-story ADU, the ordinance says "Exterior stairs are not permitted"; HCD told the city to remove that rule.

Height is measured from existing or finished grade, whichever is lower. The application and ordinance also say patio covers and covered porches are "cumulatively limited to 10% of the square footage of the proposed ADU," that skylights must be flat, not domed, and it asks you to show protected trees within 15 feet of the work and any recorded easements.

State minimums. A city's maximum ADU size can't be less than 850 sq ft, or 1,000 sq ft for an ADU with more than one bedroom. Limits on lot coverage, floor area, open space and front setbacks can't block an 800 sq ft ADU with 4-foot side and rear setbacks. The state's by-right ADUs, such as a detached ADU of up to 800 sq ft, aren't subject to local design standards. Ask Planning which standards apply to your project. [1][2][3][6]

Parking

Ordinance No. 1747-NS requires one off-street parking space for an ADU, in addition to the house's parking. It can be covered or uncovered, in a setback area, and tandem on the driveway. You don't have to replace a garage, carport or parking space you convert or tear down for an ADU.

No ADU parking space is needed when the ADU:

• is within a half-mile walk of public transit;
• is in an architecturally and historically significant historic district;
• is part of the house or an accessory structure, or is created by converting or rebuilding an existing structure;
• is where on-street parking permits are required but not offered to the occupant;
• is within one block of a car-share vehicle;
• is applied for together with a new single-family or multifamily home on the lot; or
• has 500 sq ft of interior living space or less.

State law also bars parking requirements for the state's by-right ADUs. It requires the new-home exemption only when the ADU or the lot also meets one of the other exemptions; the ordinance's list doesn't include that condition. Confirm with the Planning Division how it applies to your lot. [2][6]

Fees

The city's ADU page breaks ADU fees into three groups:

• Planning review fee: a fixed fee. The Planning fee schedule for July 1, 2025 to June 30, 2027 lists "Accessory Dwelling Unit" at $754.
• Building fees: plan check and permit fees that vary with size and value. The city says they averaged "between $2,800 and $3,200 per unit" over the past three years.
• Impact and utility fees: from the city, Conejo Valley Unified School District, police, Ventura County Fire and Conejo Recreation and Park District, plus city water and wastewater connection fees and traffic impact fees.

After you submit, the city invoices the filing fees. You must pay within 7 days or the application is voided.

Small ADUs. The city's FAQ says ADUs under 750 sq ft "are not subject to impact fees such as parkland and school fees." State law exempts ADUs of 750 sq ft or less from impact fees, but HCD's handbook says school districts may charge school fees on ADUs larger than 500 sq ft. Confirm school fees with Conejo Valley Unified before you budget. For typical costs see our ADU cost guide. [1][4][5][6]

Fire, water and building requirements

The Building Division's ADU completeness checklist (July 2026) is a list staff mark up to show what your submittal is missing. It covers:

• Fire flow and fire clearance: ask your water provider for a fire-flow test using the Ventura County Fire Department's 625 form, then send plans and results to the Fire Department. The Fire District's 610B conditions form "is required for the Application to be deemed complete." The checklist says fire sprinklers may be required based on the fire-flow data and site access; Ordinance No. 1747-NS says sprinklers aren't required in an ADU or JADU if they aren't required for the house. Ask the Building Division and the Fire Department which applies to you. Plans must show the nearest hydrant and fire access road.
• Items staff may mark as required: a geotechnical report stamped by a licensed engineer; structural plans and calculations; energy compliance forms and CALGreen sheets; and, in a Fire Hazard Severity Zone, compliance with the state's Wildland-Urban Interface Code.
• Format: all construction documents combined into one PDF, with the project labeled as an ADU, JADU or SB 9 unit.

Your water provider depends on your address: the City of Thousand Oaks ((805) 449-2400), California American Water ((805) 498-1266), Camrosa Water District ((805) 388-0226) or California Water Service ((805) 497-2757). [2][8]

Junior ADUs, renting and unpermitted units

Junior ADUs. A JADU is up to 500 sq ft and must be created inside an existing or proposed single-family home; an attached garage counts as part of the home, and new additions can't be JADUs. It needs its own entrance. It may share the house's bathroom, and if it does, it needs an inside entry to the house. You record a deed restriction on the city's form after approval. The city's FAQ says "any property with a JADU must be owner-occupied," but the 2026 ordinance requires the owner to live in the house or the JADU only when the JADU shares sanitation facilities with the house, which matches state law since 2026. HCD told the city the deed restriction itself may cover only the ban on separate sale and the JADU's size and features. See our junior ADU guide.

Renting and selling. The 2026 ordinance says an ADU or JADU "shall not be rented for a term of thirty (30) days or less," and an ADU and the house may be rented to different people. The city's FAQ says it "does not allow sale of ADUs separate from the rest of the property"; the ordinance allows it only as provided in state law (Government Code section 66341). The city asks how the unit will be occupied and what rent you expect, to report new units to the state, and reminds landlords to follow fair housing laws.

Unpermitted units. You can check a property's permit history on TO/24. To legalize an unpermitted ADU or JADU, you apply for an ADU permit. For one built before January 1, 2020, the city says it won't deny the permit for building code or local ADU rule violations unless the building is substandard under Health and Safety Code section 17920.3. If its inspector finds health and safety problems, the city says it won't penalize you for having the unit and will approve permits to fix them. It also won't charge impact fees or connection charges except where utility work is needed for safety. See our garage conversion guide for converting an existing structure. [1][2][3][5][6]

Permit steps in Thousand Oaks

1. Check your property

   Look up your property's permit history on TO/24, and check whether it is in a Fire Hazard Severity Zone and which water provider serves it. [5][8]

2. Talk to Planning

   Call the Planning Division at (805) 449-2323 or email planning@toaks.gov. Planning offers in-person and online appointments Monday to Thursday, 1:30 to 3 p.m. [5]

3. Choose a design

   Hire a designer, or browse the Thousand Oaks ADU Plans Gallery, which includes pre-approved plans. Even a pre-approved plan needs site planning for your lot. [5]

4. Get the fire-flow test and fire clearance

   Request a fire-flow test from your water provider on Ventura County Fire's 625 form, then submit plans and results to the Fire Department for its 610B conditions. [8]

5. Prepare the application

   Complete the ADU application (owner signs in two places) with a plan set, a title report and the ADU Development Tracking Form, and review the Building Division's ADU checklist. [1][5][8]

6. Submit online and pay

   Submit through the TO/24 portal. Pay the emailed invoice within 7 days or the application is voided. [1][9]

7. Plan check, permit and inspections

   After the completeness review and plan check, get your building permit and pass inspections. Building Division questions: (805) 449-2320. [8][10]

Pre-approved and sample plans

• Thousand Oaks ADU Plans Gallery

  A gallery of ADU designs linked from the city's ADU page, including pre-approved plans pre-reviewed for building code compliance; you buy or license a plan from its designer and still need site planning and a permit. [5]

Who to call

• City of Thousand Oaks Planning Division

  ADU zoning standards and appointments (planning@toaks.gov)

  (805) 449-2323

  2100 Thousand Oaks Blvd., Thousand Oaks, CA 91362

  [5][11]

• City of Thousand Oaks Building Division

  Plan check, building permits and inspections

  (805) 449-2320

  2100 Thousand Oaks Blvd., Thousand Oaks, CA 91362

  [10]

• Thousand Oaks Public Works Engineering

  Fire-flow test where the city is your water provider

  (805) 449-2400

  [8]

Questions people ask