Everything homeowners need to know about building an accessory dwelling unit in Thousand Oaks, California - size limits, setbacks, permits, and where the city's own standards have run into friction with state ADU law.
Last verified: August 2026
6/10 · Moderately ADU-friendly
1,000 sq ft*
Max ADU size
16 ft*
Max height
Not required*
Owner-occupancy
By-right
Permit type
This page summarizes Thousand Oaks Municipal Code Article 45 (Accessory Dwelling Units) plus California's statewide ADU law for general reference - it is not legal advice. Regulations change; always confirm current requirements with the Thousand Oaks Community Development Department before designing or applying for permits. See sources below.
Zoning & size requirements
What you're allowed to build
ADU type
Max size
Max height
Notes
Detached (new build)
1,000 sq ft of interior livable space
16 ft; up to 18 ft within a half mile of a major transit stop or high-quality transit corridor, plus up to 2 ft more to match the primary home's roof pitch
Must sit at least 6 ft from any other structure; no breezeways connecting it to the house; attached garage portion capped at 400 sq ft
Attached / conversion
850 sq ft or 50% of the primary dwelling's total floor area, whichever is greater
25 ft, or the height limit that applies to the primary dwelling in the underlying zone, whichever is lower
Must share at least 10 ft of wall with the main house, with no internal connecting doorway; requires its own full kitchen and bathroom
Junior ADU (JADU)
Under 500 sq ft
Within the existing walls of the home
Located entirely within a single-family home
Allowed zoning districts
ADUs and JADUs are allowed by right in every residential and mixed-use zone (R-A, R-E, R-O, R-1, R-2, R-3, RPD, HPD, and MU), on any lot with an existing or proposed dwelling, with no minimum lot size. Extra limits apply in the Protected Ridgeline Overlay zone and around protected trees, generally preserved down to a guaranteed minimum of two units of 800 sq ft or less. Confirm your parcel's zoning and overlay status with Community Development.
Additional standards
Setbacks, parking & other rules
Setbacks
4 ft from side and rear property lines for new construction; front setback matches whatever applies to the primary dwelling. Converting an existing legal structure is generally exempt from these standards
Parking
One off-street space required per ADU, in addition to parking for the primary home, unless the ADU is within a half mile of transit, in a historic district, created from converted space, 500 sq ft or smaller, or built alongside a new single- or multi-family home on the same lot
Units per lot
State-mandated ADU allowances plus one additional locally permitted ADU on single-family lots that meet the city's development standards; multi-family lots follow the separate state-mandated allowance
Owner-occupancy
Not required for an ADU. For a JADU, owner-occupancy is required only when the JADU shares sanitation facilities with the primary home; not required when it has its own separate bathroom
Rental terms
ADU and JADU rentals must run longer than 30 days; short-term rentals are not permitted
Conveyance
An ADU or JADU may be rented separately from the primary home but not sold separately, aside from a narrow state-law exception for nonprofit-built, income-qualified housing
Impact fees
Waived for ADUs under 750 sq ft; charged proportionately to the primary home's floor area at 750 sq ft and above, alongside separate city, school district, police, fire, and parks district fees
Ordinance history
How Thousand Oaks's ADU rules got here
20222021-2029 Housing Element adopted. After initially missing the state's 6th-cycle deadline, the City Council adopted its Housing Element in January 2022.
2024Article 45 rewritten. Ordinance No. 1732-NS, effective November 22, 2024, rewrote the city's ADU chapter to align with the latest wave of state ADU law, including AB 976's permanent ban on owner-occupancy mandates.
2025Further amendment, then a state compliance letter. Ordinance No. 1735-NS took effect April 25, 2025. In a September 23, 2025 letter, California HCD's Housing Policy Development Division found that ordinance failed to comply with state ADU law in six respects, including deed-restriction language, JADU construction rules, height allowances for multi-family-lot ADUs, size limits on multi-family-lot detached ADUs, and unit-combination limits below what state law requires.
2025Digital-only permitting begins. Starting September 1, 2025, all ADU plans must be submitted through the city's TO/24 Virtual Land Use Service portal; paper submittals are no longer accepted.
2026Ordinance amended again. Ordinance No. 1747-NS took effect April 10, 2026, revising the sections HCD had flagged. It is the version summarized on this page.
Worth knowing: Thousand Oaks has had to amend its ADU ordinance three times in about eighteen months, most recently after a state finding that its April 2025 rules undercounted how many ADUs and JADUs a homeowner is legally entitled to combine on one lot. If your project involves multiple units on a single-family or multi-family lot, it's worth confirming directly with Community Development that the current ordinance reflects everything state law allows.
Permit process
How Thousand Oaks ADU permitting works
1
Review the ADU checklist
Download the city's ADU Application Completeness Review handout and ADU Development Tracking Form before you start; both are required with your submittal.
2
Consider a pre-approved plan
The Thousand Oaks ADU Plans Gallery lists designs pre-reviewed for code compliance, which can speed up review; custom designs still need full plan review.
3
Submit through TO/24
All ADU applications must be submitted digitally through the TO/24 Virtual Land Use Service portal; paper submittals have not been accepted since September 1, 2025.
4
Completeness check (15 business days)
The city confirms your application is complete, or lists what's missing, within 15 business days; resubmittals are checked again on the same timeline.
5
Ministerial review & decision (60 days)
Your application is reviewed without a public hearing and approved or denied within 60 days of being deemed complete. A denial comes with a full list of deficiencies and how to fix them; appeals go to the Planning Commission within 10 calendar days.
6
Building permit & inspections
Once approved, pull your building permit and schedule inspections. ADUs relying on a septic system need California State Water Resources Control Board sign-off before the building permit is issued.
Fees and timelines are approximate - confirm current figures with Community Development, and remember your property taxes will rise based on the ADU's assessed value once it's built.
Budgeting
What it costs to build an ADU in Thousand Oaks
Garage conversion
Roughly $70,000-$180,000, generally the least expensive path since the shell already exists
Attached / interior conversion
Roughly $100,000-$220,000, depending on existing layout and utility access
New detached ADU
Roughly $150,000-$340,000 or more for a code-compliant, fully finished freestanding unit
Planning & building fees
The city reports these have averaged roughly $2,800-$3,200 per unit over the past three years, combining plan review, permit, and inspection fees
Impact & agency fees
Waived under 750 sq ft; above that, expect proportional fees from the city plus the school district, police, fire, and parks agencies serving the property
These are general ranges from local contractor estimates, regional reporting, and the city's own published figures, not quotes - actual cost depends heavily on lot conditions, finishes, and whether a septic or well system is involved.
Before you apply
Tips for a smooth approval
Check whether your lot touches a ridgeline or protected-tree overlay. The Protected Ridgeline Overlay and tree-protection rules can restrict siting well beyond the standard setbacks, especially on hillside parcels.
Set up your TO/24 account early. Since September 2025, every ADU application has to go through the digital portal, and getting comfortable with it before your submittal deadline can save time.
Ask specifically about unit combinations if you want more than one ADU. The ordinance has changed multiple times on exactly how many ADUs and JADUs can be combined on a lot, so get current, specific confirmation for your project rather than relying on a prior version of the rules.
Look into pre-approved plans. The city's ADU Plans Gallery includes designs pre-reviewed for code compliance, which can shorten your review timeline compared with a fully custom design.
Keep your ADU at 750 sq ft or less if minimizing fees is a priority. Crossing that threshold triggers proportional impact fees from the city and other public agencies.
FAQ
Common questions
Do I need to live on the property to build an ADU in Thousand Oaks?
No, not for a standard ADU. California's AB 976 permanently eliminated owner-occupancy mandates for ADUs statewide starting in 2024. For a JADU, owner-occupancy is required only if it shares a bathroom with the primary home; a JADU with its own separate sanitation facilities does not require it.
How many ADUs can I build on one lot?
Single-family lots can generally combine the state-mandated ADU allowances with one additional locally permitted ADU. Because the city has amended this section of its ordinance multiple times, including after a 2025 state finding that an earlier version undercounted allowed combinations, confirm the current rule for your specific lot with Community Development.
Do I need extra parking for an ADU?
Usually one space, which is a real requirement here rather than a blanket waiver. It's dropped if the ADU is within a half mile of transit, in a historic district, converted from existing space, 500 sq ft or smaller, or built alongside a new home on the same lot.
How long does the permit process take?
The city has 15 business days to check an application for completeness and 60 days from a complete submittal to approve or deny it, without a public hearing. Total time from design through permit issuance is typically longer once plan preparation is included.
What's the maximum size for a detached ADU?
1,000 sq ft of interior livable space, with a 16 ft height limit that can rise to 18 ft near major transit and by up to 2 more feet to match the primary home's roof pitch.
How much does an ADU cost to build in Thousand Oaks?
Garage conversions tend to run roughly $70,000-$180,000, attached or interior conversions $100,000-$220,000, and new detached units $150,000-$340,000 or more, based on local contractor estimates and regional reporting. The city separately reports that planning and building fees have averaged about $2,800-$3,200 per unit over the past three years.
Has the city's ADU ordinance had compliance problems with the state?
Yes. In a September 23, 2025 letter, California's Department of Housing and Community Development found the city's April 2025 ADU ordinance out of compliance with state law in six areas, including deed-restriction language, JADU construction requirements, height and size allowances for ADUs on multi-family lots, and how many ADUs and JADUs a homeowner can combine on one lot. The city adopted a further amendment effective April 2026 to address the sections HCD flagged.
Can I rent my ADU out on Airbnb or a short-term rental platform?
No. Thousand Oaks requires ADU and JADU rentals to be for terms longer than 30 days, which rules out short-term or vacation-rental use.
