Thousand Oaks Zoning and ADU Guide for Homeowners and Sellers

Last updated November 13, 2026. Reviewed by the Cash Home Buyers CA team. Information comes from the City of Thousand Oaks municipal code and city pages, plus California state ADU law; sources are listed at the end.

Thousand Oaks regulates accessory dwelling units (ADUs) in Article 45 of its zoning code, which was adopted in November 2024 and amended in 2025 and April 2026. If you own a house with a backyard unit, a converted garage or plans to add one, these rules decide what is legal, what can be permitted after the fact, and how a buyer will view the property.

Thousand Oaks ADU rules at a glance

These figures come from the city’s municipal code (Sections 9-4.4509 to 9-4.4512). The city’s ADU web page also points to contact information and a pre-application checklist, so start there before drawing plans.

Size, setbacks and design standards

For an attached ADU, the code allows 850 square feet or half the existing primary dwelling’s floor area, whichever is larger. Attached and converted units must share at least 10 feet of wall with the main home. A detached ADU can reach 1,000 square feet and must sit at least 6 feet from any other structure, measured wall to wall. It cannot be joined to the house by a breezeway or similar connector.

If a detached ADU comes with an attached garage, the garage portion is capped at 400 square feet. Patio covers and covered porches together are limited to 10% of the ADU’s square footage. No accessory structure may be attached to a detached ADU unless the combined area stays within the allowed ADU size. Hillside lots deserve extra attention: the code bars any ADU on a natural slope steeper than 25%.

State-mandated ADUs

Separate from the local standards, Section 9-4.4511 recognizes state-mandated ADUs. These include a unit created inside the existing space of a single-family home or an existing accessory structure, with up to 150 additional square feet allowed for entry and exit.

They also include one new detached ADU of up to 800 square feet with 4-foot side and rear setbacks, with height allowances of 16 feet, or 18 feet near a major transit stop, plus 2 feet to match the roof pitch of the main house.

On lots with existing multifamily buildings, the code allows more detached units, up to eight or as many as there are existing units, whichever is fewer.

California’s HCD reviewed the city’s ordinance in September 2025 and sent a letter listing sections that needed changes, including height limits and size restrictions for multifamily lots. Cities have to bring ordinances in line with state law, so the code text can change; always check the current version.

Junior ADUs

A JADU is carved out of an existing single-family home, with a maximum of 500 square feet and a minimum equal to an efficiency unit. Under state law, a JADU generally comes with owner-occupancy and deed restriction conditions, so a buyer needs to know whether those apply to the property they are purchasing.

State law that applies in Thousand Oaks

California’s ADU statutes (Government Code sections 66310 to 66342) require cities to process complete ADU applications ministerially, generally within 60 days, and to allow at least one ADU and one JADU on most single-family lots. State law also limits impact fees for smaller units: ADUs under 750 square feet are not charged impact fees. The California Department of Housing and Community Development (HCD) publishes a plain-language ADU page and checklist for homeowners.

What if the unit was built without a permit?

Garage conversions and backyard units built without permits are common across Ventura County. Start by asking the city’s Building Division what is on file for your address.

Options usually include applying for a retroactive permit, which may require opening walls for inspection, bringing the unit up to current code, or selling the property with the issue disclosed. Compare the cost and time of legalization to what a buyer would pay for the property today.

Our Thousand Oaks building permits guide covers how to reach the Building Division and the TO/24 online portal, and our code enforcement guide explains complaints and notices.

How an ADU affects a sale

A permitted ADU can add value and appeal to buyers who want rental income or space for family. An unpermitted unit does the opposite for many buyers: lenders may not count it, appraisers may value only the permitted square footage, and agents must disclose known unpermitted work.

Our statewide guide to selling as-is with unpermitted work explains what California sellers must disclose. A cash buyer can purchase without the unit being legalized and price the risk into the offer.

How to sell a house in Thousand Oaks with an ADU or unpermitted unit

1. Pull the records. Ask Community Development what permits are on file for the address.
2. Confirm what you have. Measure the unit and note slope, setbacks and whether it is attached or detached.
3. Weigh the options. Legalize it, sell with a price credit, or sell as-is for cash.
4. Disclose honestly. A cash offer does not change what you must disclose.

See selling a house as-is in Thousand Oaks or our cash-offer process.

Questions about your house? Call (424) 435-2326 or request a cash offer. No cost, no obligation.

What the city asks for with an ADU application

The Community Development Department publishes an ADU submittal checklist that is stricter than many owners expect.

It asks for a stamped geotechnical report, Title 24 Part 6 energy forms, the 2025 CALGreen mandatory measures, structural plans and calculations, and compliance with Chapter 5 of the Wildland-Urban Interface Code on lots in Fire Hazard Severity Zones.

Plans must be submitted as a single combined PDF with text no smaller than one eighth of an inch, and the sheets must include a cover sheet, site plan, floor plan, roof plan, elevations, sections and details, along with easements and the nearest fire hydrant. An ADU Development Tracking Form is part of the package.

Fire flow and fire clearance

Fire clearance is a separate step that can add weeks. You request a Fire Flow Test from your water purveyor, which may be the City of Thousand Oaks, Cal-Am, Camrosa or Cal Water, complete Section 1 of Form 625 and send it to Ventura County Fire at (805) 389-9738.

The fire department returns its conditions, and you email those to your plan checker or to building@toaks.gov. Starting this step early keeps the permit from stalling after plan check. Questions about the planning side go to (805) 449-2323 or planning@toaks.gov, and building questions go to (805) 449-2500.

Permit timing and legalizing an existing unit

Chapter 4 of the municipal code sets deadlines that apply to ADU projects. An application expires after 180 days, with a 90-day extension available, and an issued permit expires if work does not start within 365 days or 365 days pass after the last successful inspection.

A permit to legalize unpermitted work is shorter: it expires in 90 days and can be extended once by up to 90 days if you ask in writing before it expires.

The city can also deny a new permit while noticed violations are open on the property, unless the permit is needed to fix them. See the permits guide for the full list.

Checklist for sellers with an ADU

• Ask Community Development for permit and inspection records on every unit at the address.
• Confirm whether the unit has a final inspection or an open or expired permit.
• Gather the plans, the geotechnical report and any fire clearance letters.
• Note whether the unit is rented and collect leases and rent records.
• Compare the cost of legalizing with the price a buyer would pay for the property as it is.

Thousand Oaks ADU FAQ

How big can a detached ADU be in Thousand Oaks?

The municipal code allows a detached ADU of up to 1,000 square feet of livable space, with 4-foot side and rear setbacks.

How big can a junior ADU be?

A JADU can be up to 500 square feet and must be created within an existing single-family home.

Can I build an ADU on a steep lot?

Not on a natural slope steeper than 25% under the city’s code.

Who do I call with ADU questions?

Community Development at (805) 449-2500, 2100 Thousand Oaks Blvd.

What does the city ask for with an ADU application?

A stamped geotechnical report, Title 24 energy forms, CALGreen measures, structural plans and calculations, and a fire clearance in fire hazard zones, submitted as one combined PDF.

How long does a legalization permit last?

90 days, with one written extension of up to 90 days requested before it expires.

Can I sell a Thousand Oaks house with an unpermitted unit?

Yes, with disclosure. A cash buyer can purchase it as-is and price the risk into the offer.

Sources

• Thousand Oaks Municipal Code, Article 45: Accessory Dwelling Units
• City of Thousand Oaks: Accessory Dwelling Units
• California HCD: Review of Thousand Oaks ADU ordinance (Sept. 2025)
• California HCD: Accessory Dwelling Units

This guide is general information, not legal advice. Rules change; confirm requirements with the City of Thousand Oaks.