What can you build, and what will it cost?
Ventura County. Type your address and the county's own records fill in the rest — then it reads the adopted ordinance and the adopted fee schedule.
Pick your address from the list. The house size comes from the county assessor's record and is not typed in — it is the figure the city will work from. The ADU size starts at half the house, rounded, and stays within the calculator's existing estimate range. Your manually entered area is preserved; if the applicable rule or required data is not validated for it, the fee total is withheld for site-specific review. The lot size fills in too and you can correct it.
What you can build
Fees
Estimate only. The numbers may be wrong. They are read from published ordinances and adopted fee schedules, which change, contain errors, and are applied differently case by case. House and lot sizes come from Ventura County assessor records and are an estimate, not a measured survey. This is not a quote, a permit determination, a zoning clearance, or legal advice, and no professional relationship is created by using it. Fine Craftsmanship, Inc. accepts no liability for any decision made on these figures. Confirm every number with the jurisdiction and the school district before you rely on it.
The rest needs the parcel: your real setbacks, easements, the fees your city does not publish, and whether the lot is in the Coastal Zone.
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What each city allows
The rules California sets for every city
A local agency has to allow an accessory dwelling unit of at least 800 square feet with four-foot side and rear setbacks (Gov. Code §66321). A junior ADU is capped at 500 square feet of interior livable space inside the walls of the house (§66313). Development impact fees are exempt at or under 750 square feet (§66311.5(c)(1)); school fees are exempt under 500 square feet (§66311.5(c)(3)), and the statewide Level 1 cap rose to $5.38 per square foot in January 2026 under SB 543. Added parking falls away within half a mile walking distance of transit (§66322(a)(1)).
Ventura County, city by city
Preliminary reference only. The applicable size depends on the property, unit type and approval route. The calculator retains its existing estimate rules while local rules are reviewed. Inputs outside that range or lacking a validated size rule are preserved, with no fee total shown pending site-specific review.
| Jurisdiction | ADU size guidance — site review required | Setbacks | Decision |
|---|---|---|---|
| Santa Paula | Half the house, held between 800 and 1,200 sq ft | 20 ft front · 4 ft side and rear | Generally 60 days after a complete application; statutory exceptions apply |
| Oxnard | 850 sq ft detached; attached is half the house, 800 to 1,200 sq ft | 4 ft side and rear | 15 business days for completeness; generally 60 days after a complete application for approval or denial, subject to statutory exceptions |
| Ventura | The ordinance says 1,200 sq ft; the city's own page says 850 to 1,000. Unresolved, so the calculator prints no number | 4 ft side and rear | Generally 60 days after a complete application; statutory exceptions apply |
| Ventura County, unincorporated | 850 sq ft; 1,200 sq ft above a 9,000 sq ft lot; 1,800 sq ft at ten acres | 4 ft side and rear | Generally 60 days after a complete application; statutory exceptions apply |
| Camarillo | 850 sq ft; 1,200 sq ft on a lot of an acre or more | 4 ft side and rear | Generally 60 days after a complete application; statutory exceptions apply |
| Simi Valley | 1,000 sq ft; 1,200 sq ft on a lot over 8,000 sq ft | 4 ft side and rear · 6 ft from the house | Generally 60 days after a complete application; statutory exceptions apply |
| Ojai | 85% of the house, capped at 850 sq ft | 4 ft side and rear | Ministerial |
| Port Hueneme | 800 sq ft is a protected state-law allowance under a specific approval route, not a universal maximum. A standard detached ADU may qualify for up to 1,200 sq ft, depending on the property and approval route. Port Hueneme repealed its local ADU ordinance in December 2024. | 4 ft side and rear, state minimum | 15 business days for completeness; generally 60 days after a complete application for approval or denial, subject to statutory exceptions |
| Thousand Oaks | The city renumbered its ADU article in April 2026 and the size limits are not retrievable, so the calculator prints no number | State minimum | 15 business days for completeness; generally 60 days after a complete application for approval or denial, subject to statutory exceptions |
Timing and size guidance reviewed October 3, 2026. Completeness review and permit approval are separate steps. For an existing primary dwelling, approval or denial is generally due within 60 days after a complete application, subject to statutory conditions and exceptions; applications with a new primary dwelling and applicant-requested delays can affect timing. Sources: California SB 543, Port Hueneme Planning and Zoning, and HCD ADU Handbook, March 2026.
Where the property figures come from
House floor area, year built and lot size are read from the Ventura County assessor and GIS record for the parcel at the address you enter. They are the figures a city plan checker works from, and they are an estimate rather than a measured survey. Where the county holds no floor area for a parcel — a mobile home, some condominiums — the calculator says so and names the office that holds it.