ADU Rules in Thousand Oaks (2026): What You Can Build

An accessory dwelling unit (ADU) is a second, self-contained home with its own kitchen, bathroom and entrance on the same lot as your house. Thousand Oaks permits ADUs and junior ADUs under California state ADU law (Government Code 66310–66342) and its own ordinance, Article 45 of the Thousand Oaks Municipal Code, adopted in November 2024 and amended in April 2026. Green Design and Build is a licensed general contractor (CSLB #1110975) serving homeowners across Los Angeles County, Orange County, Ventura County, western Riverside County and western San Bernardino County. The headline: on any single-family lot in Thousand Oaks, the city must approve a detached ADU of at least 800 sq ft, 16 ft tall, with 4 ft side and rear setbacks, in a 60-day ministerial review.

Who we are

Green Design and Build is led by Dekel Sofer; we have completed hundreds of projects and hold a 4.7-star rating across 146 Yelp reviews. We are a full-service residential general contractor and design-build remodeler, not an ADU specialist: we build ADUs and garage conversions alongside kitchens, bathrooms, additions and whole-home renovations. Our Thousand Oaks contractor page covers the rest.

ADU rules in Thousand Oaks at a glance

Rule	Thousand Oaks (2026)
Detached ADU, max size	800 sq ft guaranteed by state law with 4 ft setbacks and no lot-coverage test. One larger “local-standard” ADU is also allowed (Sec. 9-4.4509); state law requires that cap to be at least 850 sq ft (studio/one bedroom) or 1,000 sq ft (two or more bedrooms), and never more than 1,200 sq ft.
Attached ADU, max size	Up to 50 percent of the existing house, but never less than 800 sq ft.
Junior ADU (JADU)	Up to 500 sq ft inside the walls of the house (attached garage counts), efficiency kitchen, own entrance. One per lot.
Height	16 ft detached; 18 ft (+2 ft for roof pitch) within half a mile of a major transit stop; attached ADU up to 25 ft or the zone limit, whichever is lower.
Setbacks	4 ft side and rear for new units. Conversions keep existing setbacks; only fire and safety clearances apply.
Parking	None for conversions, units within half a mile of public transit, or the other Gov. Code 66322 cases; otherwise at most one space per unit or bedroom. Replacement parking never required for a converted or demolished garage.
Owner-occupancy	Not allowed as a condition for an ADU. JADU: only when it shares a bathroom with the house (Sec. 9-4.4506).
Units on a single-family lot	One converted ADU or JADU, one new 800 sq ft detached ADU and one JADU under state law; the city adds one local-standard ADU (Sec. 9-4.4504).
Short-term rental	Not permitted; rentals must be longer than 30 days. No separate sale.
Impact fees	None under 750 sq ft; proportional above. School fees only at 500 sq ft and up. City says building fees average $2,800–$3,200 per unit.
Review timeline	Ministerial, no hearing. Completeness in 15 business days; approve or deny within 60 days of a complete application.
Where to apply	Community Development Department, Planning Division, 2100 Thousand Oaks Blvd, Thousand Oaks, CA 91362, via the TO/24 online portal. (805) 449-2323, planning@toaks.gov.

Size, height and setbacks

Government Code 66323 requires the city to approve a new detached ADU of up to 800 sq ft with 4 ft side and rear setbacks on any lot with a single-family house, and Government Code 66321 bars any lot-coverage, floor-area-ratio, open-space, front-setback or minimum-lot-size rule from blocking it. On a typical 8,000–12,000 sq ft Conejo Valley ranch lot, it fits in the rear yard without a variance.

Above 800 sq ft, the local ordinance takes over. Article 45 allows one additional ADU built to the city’s own standards (Secs. 9-4.4509 and 9-4.4510), which state law bounds at no less than 850 sq ft for a studio or one-bedroom, 1,000 sq ft for two or more bedrooms, 50 percent of the house for an attached unit, and no more than 1,200 sq ft detached. In that range the city’s local setbacks, lot coverage and design standards apply; we confirm them for your zone before we draw.

Height is 16 ft for a detached unit, or 18 ft plus 2 ft for roof pitch within half a mile of a major transit stop, which few Thousand Oaks lots are. Plan on a single story under 16 ft unless the ADU is attached, where 25 ft or the zone limit applies.

Three local twists. ADUs are allowed in the R-A, R-E, R-O, R-1, RPD and HPD zones and adopted specific plans, but the ordinance keeps units off natural slopes steeper than 25 percent and away from spots that would push defensible-space obligations onto a neighbor. The oak tree ordinance is not waived: a foundation, trench or equipment inside an oak’s protected zone needs an oak tree permit, and the site plan must show every oak and its dripline. And the foothill and canyon neighborhoods of Thousand Oaks and Newbury Park sit in Very High Fire Hazard Severity Zones under the Ventura County Fire Department, where an ADU gets Chapter 7A ignition-resistant exteriors, Class A roofing and ember-resistant vents. None of these stops the 800 sq ft unit; they decide where it goes and what it is built from.

Garage conversions and JADUs in Thousand Oaks

A garage conversion is the least regulated ADU in Thousand Oaks. Because it sits inside an existing structure, it keeps the garage’s setbacks, may be expanded by up to 150 sq ft solely for an entrance or exit, needs no parking, and the city cannot make you replace the two garage spaces you lose. A conversion also needs no new or separate utility connection; it runs off the house’s existing service, though a 1960s 100-amp panel usually needs an upgrade to carry a second kitchen.

Fire sprinklers follow the main house: under Sec. 9-4.4507 they are not required in the ADU or JADU if not required in the primary dwelling, and the ADU never triggers a retrofit of the house.

A junior ADU is the smallest option: up to 500 sq ft carved out of the house or its attached garage, with an efficiency kitchen, its own exterior entrance, and either its own bathroom or interior access to the family bathroom. It is exempt from impact fees, needs no parking, and can be permitted alongside a detached ADU, which is how one lot ends up with three homes. A JADU requires a recorded deed restriction against separate sale; if it shares a bathroom with the house the owner must live in the house or the JADU, and if it has its own bathroom the 2026 ordinance drops that requirement.

Pre-approved plans, fees and utilities

Thousand Oaks runs a pre-approved plan program, the Thousand Oaks ADU Plans Gallery, with designs from several architects the city has already reviewed. A gallery plan shortens plan check, but the city is explicit that every plan, pre-approved or not, still requires customized site planning and permitting for your property. Flat, oak-free lots outside the fire zone get the most from a gallery plan; on a hillside or oak-covered lot, a custom design often costs no more once the site work is counted. The City of Los Angeles has a parallel program, covered on our LA Standard Plan Program page.

Fees fall into four groups. Planning review is a fixed fee. Building permit and plan-check fees vary; the city publishes an average of $2,800–$3,200 per unit. Impact fees (school, police, fire, recreation district, traffic) and water and wastewater connection charges apply only above the state thresholds: nothing under 750 sq ft, proportional above, school fees from 500 sq ft. Property taxes rise by the assessed value of the new unit only.

Utilities follow Government Code 66324 and Sec. 9-4.4507. A conversion cannot be required to have a separate connection or pay a connection fee or capacity charge; the city does require a new or separate connection for other ADUs, with any fee proportionate to the unit’s size or fixture count. Electrical service is Southern California Edison. Lynn Ranch and rural-edge lots on septic must prove septic capacity alongside the ADU application.

The permit process in Thousand Oaks, step by step

1. Site check. Zone, fire-hazard designation, specific plan, oak survey and CC&Rs. HOAs in Dos Vientos, Lang Ranch, Westlake and Newbury Park can review the design but cannot prohibit an ADU or restrict it unreasonably under state law.
2. Design. A gallery plan adapted to the lot, or a custom set: architectural, structural, Title 24 energy, site and grading, and utility plans.
3. Submit through TO/24. Application, the city’s ADU Development Tracking Form and the plan set are uploaded online; Planning confirms completeness within 15 business days.
4. Plan check. The 60-day clock starts when the application is complete. Planning checks zoning, the Building Division checks structural, energy, fire and plumbing, and Ventura County Fire reviews fire-zone projects. Corrections are answered in TO/24.
5. Permit issuance. Plan-check, permit, school and any impact and connection fees are paid; any oak tree permit issues alongside.
6. Construction and inspections. Foundation through final, scheduled through TO/24.
7. Certificate of occupancy. Issued after final; the ADU cannot receive its certificate before the main house has one.

Correction cycles, HOA review and oak permits add time around the 60-day clock. End to end, a Thousand Oaks ADU takes six months to a year, a garage conversion at the short end and a fire-zone hillside unit at the long end.

What an ADU costs in Thousand Oaks

Our published ranges apply here: a garage conversion typically runs $100,000–$200,000; a detached 500 sq ft ADU $180,000–$260,000; a 700–800 sq ft unit $225,000–$350,000; and a 1,000 sq ft unit $300,000–$450,000 or more. The rule of thumb is $300–$450 per sq ft all-in, and $500 or more per sq ft on difficult lots.

Two local drivers push Thousand Oaks toward the upper half: fire-zone construction (ignition-resistant siding, Class A roofing, tempered glazing, ember-resistant vents) and hillside or oak-constrained lots (engineering, grading, retaining walls, a longer utility run to where the unit can legally sit). Flat 1960s tracts with a garage to convert land near the bottom. Our guide to how much it costs to build an ADU walks through a real project budget, why ADU quotes vary so much explains what to compare between bids, and the ADU rules calculator shows the state-law floor for your lot.

Frequently asked questions

How big of an ADU can I build in Thousand Oaks?

In Thousand Oaks, state law guarantees a detached ADU of at least 800 sq ft with 4 ft side and rear setbacks on any single-family lot, regardless of lot coverage. The city also allows one larger ADU under its local standards, which state law requires to be at least 850 sq ft for a studio or one-bedroom and 1,000 sq ft for two or more bedrooms, up to a statewide ceiling of 1,200 sq ft.

How tall can an ADU be in Thousand Oaks?

A detached ADU in Thousand Oaks may be 16 ft tall, or 18 ft plus 2 ft for roof pitch if the lot is within half a mile of a major transit stop. An attached ADU may reach 25 ft or the zone’s height limit, whichever is lower. Most Thousand Oaks lots qualify only for the 16 ft standard, which fits a single-story unit with a pitched roof.

Do I need to add parking for an ADU in Thousand Oaks?

Usually not. Thousand Oaks cannot require parking for a garage or house conversion, for an ADU within half a mile of public transit, or in the other cases in Government Code 66322, and may require at most one space per unit or bedroom otherwise. If you convert or demolish your garage for the ADU, the city cannot require you to replace the lost spaces.

Can I rent my Thousand Oaks ADU on Airbnb?

No. Thousand Oaks Municipal Code Sec. 9-4.4506 prohibits renting an ADU or JADU for a term of 30 days or less, matching state law. ADUs may be rented long-term to tenants separate from the main house, and the owner does not have to live on the property, but the ADU cannot be sold separately from the house.

Do I have to live on the property if I build an ADU in Thousand Oaks?

Not for an ADU: state law bars Thousand Oaks from imposing an owner-occupancy requirement on accessory dwelling units. For a junior ADU, the city’s 2026 ordinance requires the owner to live in the house or the JADU only when the JADU shares bathroom facilities with the house; a JADU with its own bathroom has no owner-occupancy requirement.

How long does an ADU permit take in Thousand Oaks?

Thousand Oaks must confirm a complete ADU application within 15 business days and approve or deny it within 60 days, with no public hearing. Corrections, HOA review, oak tree permits and fire-zone review happen around that clock, and including design and construction a Thousand Oaks ADU takes six months to a year from first meeting to certificate of occupancy.

Find out what fits on your Thousand Oaks lot

Send us your address and we will check the zone, the oaks, the fire map and the setbacks, then tell you which ADU the city will approve and what it should cost. Site visits and written estimates are free.