ADU Rules in Ventura County, California
We track 4 cities in Ventura County. Each city writes its own ADU ordinance on top of California law, so size limits, fees, and design rules differ from one city to the next. Among the cities we track, Thousand Oaks has the lowest starting permit fees ($4,000 – $16,000).
Cities
4
Max Detached Size
1,000–1,200 sq ft
Build Costs From
$150,000
Pre-approved Plans
1 of 4 cities
Ventura County Cities Compared
| City | Max detached | Height | Permit fees | Build cost |
|---|---|---|---|---|
| Oxnard | 1,200 sq ft | 25 ft and two stories (attached and detached) | $7,000 – $15,000 | $150,000 – $320,000 |
| Simi Valley | 1,200 sq ft | 16 ft (detached) | $7,000 – $14,000 | $155,000 – $310,000 |
| Thousand Oaks | 1,000 sq ft | 16 ft (detached) | $4,000 – $16,000 | $150,000 – $400,000 |
| Ventura | 1,000 sq ft | 18 ft (detached) | $7,000 – $14,000 | $160,000 – $325,000 |
Oxnard ADU rules
Oxnard accepts pre-approved ADU plans under AB 1332, though a project-specific site plan, energy calculations and structural calculations may still be required. Coastal Zone parcels near the beaches and harbor may need a Coastal Development Permit, which adds time. Confirm whether your lot is in the Coastal Zone before design work starts.
Simi Valley ADU rules
Simi Valley regulates ADUs in Development Code Section 9-44.160 and the city says the ordinance is being updated again after state (HCD) review of earlier versions. Valley-floor lots are mostly flat and roomy, while hillside lots in the north of the city can need geotechnical work for new foundations. Ventura County Fire reviews ADU plans.
Thousand Oaks ADU rules
Thousand Oaks runs an ADU Plans Gallery with pre-approved designs, which is the fastest route to a permit, though you still need a site plan for your lot. The city applies objective design rules: detached ADUs must borrow at least one wall material and one color from the main house and follow its roof pitch. Hillside lots may fall under the Hillside Grading Ordinance, and many neighborhoods have HOAs.
Ventura ADU rules
The City of Ventura provides free standardized plans for detached ADUs, which saves the cost and time of a custom design. Detached ADUs can be 18 ft tall, or 20 ft to match the main house roof pitch, and attached ADUs can reach the zone height limit. Parcels in the Coastal Zone may need a Coastal Development Permit, which adds time.
Rules that apply in every California city are summarized in our California ADU law guide. See all California cities or compare every city side by side.