California's ADU laws have moved more in the last six years than in the prior thirty. Owner-occupancy is no longer required statewide, parking exemptions have expanded, setbacks are floor-capped at 4 feet, and AB 1033 (2023) opened the door to selling ADUs as condominiums. I'm Brian Cooper, REALTOR(R) at eXp Realty (DRE# 01434286). I work with Simi Valley, Thousand Oaks, and Moorpark ADU owners and shoppers. Here's the 2026 city-by-city playbook.
Quick Answer
California Government Code 65852.2 sets the statewide floor for ADU permitting. Local cities can be more permissive but generally cannot be more restrictive than the state floor on most single-family lots. The state mandates: 4-foot side and rear setbacks (no front setback exception in most cases), 16-foot height for detached single-story (18 feet for two-story or when within half-mile of major transit), 1,200 sqft maximum for detached ADUs, no owner-occupancy requirement for ADUs permitted on or after January 1, 2020 (sunset through January 1, 2025; extended by AB 976 in 2023). JADUs under Gov Code 65852.22 are capped at 500 sqft and must be within the existing single-family footprint with owner-occupancy required.
On top of the state floor, each Ventura County city has a local ordinance: Simi Valley at Title 9, Chapter 9-44; Thousand Oaks at TOMC 9-4.3415 plus Hillside Ordinance interactions; Moorpark at Chapter 17.28. None of the three currently prohibit ADUs on single-family lots. AB 1033 (2023) allows jurisdictions to opt in to ADU condominium sale — verify current opt-in status per city. ADU rental income can be counted toward refinance qualifying under Fannie Mae and Freddie Mac rules updated in 2023 and 2024.
California ADU/JADU baseline (Gov Code 65852.2/65852.22)
The state ADU statute is layered. Section 65852.2 governs Accessory Dwelling Units. Section 65852.22 governs Junior Accessory Dwelling Units. SB 9 (2021) added urban-lot-split provisions at Gov Code 65852.21 that interact with but do not replace ADU law. AB 976 (2023) made permanent the owner-occupancy prohibition for ADUs. AB 1033 (2023) created the condominium-conversion path.
Mandatory state floor as of 2026:
- Detached ADU: max 1,200 sqft (jurisdiction may permit larger).
- Attached ADU: 50% of primary dwelling sqft up to 1,200 sqft.
- JADU: max 500 sqft, within existing single-family footprint, includes interior connection to primary dwelling, separate entry; owner-occupancy of either the primary or the JADU required.
- Setbacks: 4-foot side and rear minimum; no minimum from existing residence; front setback per local ordinance for the underlying zone.
- Height: 16 feet for detached single-story on single-family lot; up to 18 feet within half-mile of major transit or for second-story addition; 25 feet for multifamily-lot detached ADUs.
- Parking: one space per ADU unless the lot is within half-mile of high-quality transit, in a historic district, part of the existing primary residence, on an alley, or where on-street parking permits are required but unavailable to the ADU tenant.
- Owner-occupancy: NOT required for ADUs (post-2020 permits, made permanent by AB 976). Required for JADUs.
- Approval timeline: 60-day ministerial review (no discretionary review, no public hearing).
Simi Valley (Title 9, Chapter 9-44)
Simi Valley's ADU ordinance is at Title 9, Chapter 9-44 of the Simi Valley Municipal Code. The city completed its most recent ADU ordinance update in alignment with state law. Single-family lots in all R-1 zones allow ADUs and JADUs ministerially.
Simi Valley specifics worth knowing:
- Maximum detached ADU size: 1,200 sqft (with 850 sqft studio / 1,000 sqft one-bedroom limits that California Gov Code 65852.2(c)(2) requires jurisdictions to allow).
- Setbacks: 4 feet side and rear per state floor.
- Height: 16 feet detached single-story; 18 feet for second-story over garage or attached.
- Parking: one space required unless statutory exemption applies. Simi Valley has limited transit; the half-mile-from-high-quality-transit exemption applies to some areas near the Metrolink station only.
- Owner-occupancy: not required for ADUs; required for JADUs.
- Short-term rental: Simi Valley prohibits ADU use as a short-term rental (under 30 days). Long-term (30+ days) is permitted.
- Permit fees: typically $4,000-$8,000 in total city/county/utility fees for a standard detached ADU.
Thousand Oaks (TOMC 9-4.3415 + Hillside Ordinance)
Thousand Oaks regulates ADUs at Thousand Oaks Municipal Code Section 9-4.3415. Standard R-1 lots across the city allow ADUs and JADUs ministerially. The Hillside Ordinance (TOMC 9-4.3501 et seq.) layers on top in designated hillside areas — Lang Ranch, Dos Vientos, North Ranch hillside, and other slope-designated parcels.
On hillside lots, the Hillside Ordinance affects ADU siting through grading limits, slope-specific setbacks, and natural feature preservation rules. The Hillside Ordinance does not prohibit ADUs but can narrow feasible footprint on lots with significant slope. Thousand Oaks also has neighborhood-specific HOA overlays in many tracts that govern ADU design review on top of TOMC permitting.
Thousand Oaks specifics:
- Maximum detached ADU: 1,200 sqft per state floor.
- Setbacks: 4 feet side and rear per state floor.
- Height: 16 feet detached single-story; 18 feet within half-mile of high-quality transit corridor.
- Parking: one space; transit-corridor exemption (Highway 101 corridor) applies broadly.
- Hillside Ordinance: additional grading and design review required for slope parcels.
- HOA overlay: many Thousand Oaks tracts (Lang Ranch, Dos Vientos, Lynn Ranch) have HOAs that conduct architectural review separate from the city. Verify before designing.
- Permit fees: typically $5,000-$10,000 city/county/utility for a standard detached ADU.
Moorpark (Chapter 17.28)
Moorpark regulates ADUs at Municipal Code Chapter 17.28. The city updated the ordinance in line with state law and accepts ministerial ADU applications on single-family-zoned lots. Moorpark's lot stock skews newer and larger than Simi Valley, which often makes siting easier.
Moorpark specifics:
- Maximum detached ADU: 1,200 sqft per state floor.
- Setbacks: 4 feet side and rear per state floor.
- Height: 16 feet detached single-story; 18 feet two-story.
- Parking: one space required; transit-corridor exemption is limited (Moorpark Metrolink station footprint).
- Owner-occupancy: not required for ADUs.
- HOA overlay: many Moorpark Highlands and newer-construction tracts have HOAs requiring architectural review.
- Permit fees: typically $4,500-$9,000 in total city / Ventura County / utility fees.
Per-city ADU rules matrix
Side-by-side comparison of the three jurisdictions' ADU rules as of 2026.
| Rule | Simi Valley | Thousand Oaks | Moorpark |
|---|---|---|---|
| Code section | Title 9 Ch 9-44 | TOMC 9-4.3415 | Ch 17.28 |
| Max detached ADU | 1,200 sqft | 1,200 sqft | 1,200 sqft |
| Side / rear setback | 4 ft | 4 ft | 4 ft |
| Height (single-story) | 16 ft | 16 ft | 16 ft |
| Height (two-story / transit) | 18 ft | 18 ft | 18 ft |
| Owner-occupancy required (ADU) | No | No | No |
| Owner-occupancy required (JADU) | Yes | Yes | Yes |
| Transit parking exemption applies | Limited | Broad (101 corridor) | Limited |
| Hillside Ordinance overlay | No | Yes (slope parcels) | No |
| HOA architectural review | Some tracts | Many tracts | Many tracts |
JADUs — Junior Accessory Dwelling Units
A JADU is a smaller subset of ADU. Under Gov Code 65852.22, a JADU is no more than 500 sqft, must be contained entirely within the existing single-family footprint, may have a separate exterior entry, must include an efficiency kitchen, and may share a bathroom with the primary dwelling.
Owner-occupancy IS required for JADUs. The owner can occupy either the JADU or the primary dwelling but one of the two must be owner-occupied. Sale (condominium-style) is not currently permitted for JADUs even under AB 1033.
Practical use: JADUs work well as a converted bedroom or attached studio with a private entrance. They're cheaper to build than detached ADUs and faster to permit. The 500-sqft cap and owner-occupancy requirement limits them to family or modest rental use.
AB 1033 — sellable ADUs as condominiums
AB 1033 (2023) added Gov Code 66325 et seq., creating a framework under which a city or county may opt in to allow an ADU to be sold separately from the primary dwelling as a condominium. The mechanism: the owner files a condominium plan, the lot is subjected to a tract or parcel map, and the ADU becomes a separately deeded unit.
Critical: AB 1033 is opt-in for each jurisdiction. A city or county does not have to allow ADU condominium conversion. As of 2026, several Bay Area cities have opted in (Berkeley, San Jose). In Ventura County, opt-in status is fluid — Simi Valley, Thousand Oaks, and Moorpark have not all formally opted in. Calabasas adopted the HCD Standard ADU Plans but the condo conversion opt-in is a separate vote. Verify current opt-in status before counting on the condominium sale path.
Even without local opt-in, AB 1033 is relevant because an opt-in could substantially raise the value of existing ADUs — converting them from rental-income assets to separately-deeded resale units.
California Pre-Approved ADU Plans (HCD)
The California Department of Housing and Community Development (HCD) operates the Statewide ADU Pre-Approved Plan Program through DGS. Approved standard plans cut design and permit time meaningfully. Calabasas adopted the HCD Standard ADU Plans in 2023, creating a path to approval as quick as 30 days for qualifying lots.
Simi Valley, Thousand Oaks, and Moorpark have not all formally adopted the HCD Standard Plans, though all three accept pre-approved plans from licensed designers as a fast-track option. Whether to pursue a Standard Plan, a custom plan, or a precast modular ADU depends on lot specifics. For tight lots in infill Simi Valley, custom design usually fits better. For wide-open lots in Moorpark or Wood Ranch, Standard Plans can save 4-6 weeks of design.
ADU rental income for refinance qualifying
Fannie Mae updated Selling Guide B3-3.1-08 in 2023 to expressly recognize ADU rental income for qualification on the primary residence refinance. The rule: documented rental income from the ADU (lease + deposit) can be added to the borrower's qualifying income on the same residence's refinance. Up to 30% of qualifying income can come from ADU rental (higher percentages allowed on specific products).
Freddie Mac has similar guidance through Loan Product Advisor. FHA also recognizes ADU rental income but the documentation requirements are stricter. VA treats ADU rental as residual income only.
Practical impact: a permitted ADU renting at $2,500/month adds roughly $30,000 of qualifying income, which can buy approximately $250,000-$300,000 of additional borrowing capacity on a refinance. For owners considering an ADU as an investment, the refinance leverage often pays the construction cost over 24-36 months of operation.
ADU cost ranges — soft vs hard (2026)
Total ADU cost in Simi Valley, Thousand Oaks, and Moorpark in 2026 typically runs $150-$400 per sqft all-in. The variance is driven by lot conditions, design complexity, utility connections, and finish level. Here's the breakdown.
| Cost category | Typical range 2026 |
|---|---|
| Design / plans / engineering | $8,000-$20,000 |
| City permits + impact fees + school fees | $5,000-$12,000 |
| Hard construction (detached, full finish) | $140-$340/sqft |
| Hard construction (garage conversion) | $80-$180/sqft |
| Utility connections (sewer, water, electric panel) | $5,000-$25,000 |
| Site work / grading / hardscape | $5,000-$30,000 |
| Total typical detached 800 sqft ADU | $240,000-$320,000 all-in |
Frequently Asked Questions
Do I need owner-occupancy to build an ADU in Ventura County?
No for ADUs. AB 976 (2023) made permanent the prohibition on owner-occupancy requirements for ADUs permitted on or after January 1, 2020. JADUs under Gov Code 65852.22 do still require owner-occupancy of either the primary or the JADU.
What's the maximum ADU size in Simi Valley, Thousand Oaks, or Moorpark?
Detached ADUs: 1,200 sqft maximum per state floor (all three cities follow this). Attached ADUs: 50% of primary dwelling sqft up to 1,200 sqft. JADUs: 500 sqft within existing footprint. Cities must allow at least an 850 sqft studio / 1,000 sqft one-bedroom regardless of other restrictions.
Do I need to provide parking for an ADU?
One space is the default. Exemptions apply if the lot is within half-mile of high-quality transit, in a historic district, the ADU is within the existing primary residence, on an alley, or where on-street permits would be required but aren't available to ADU tenants. Thousand Oaks has broad 101-corridor transit-exemption application; Simi Valley and Moorpark have narrower exemption zones.
Can I sell my ADU separately under AB 1033?
Only if the jurisdiction has opted in. AB 1033 (2023) created the framework but left adoption to cities and counties. As of 2026, Simi Valley, Thousand Oaks, and Moorpark have not all formally opted in. Verify current opt-in status with city planning before assuming the condo conversion path is available.
Can I count ADU rental income toward a refinance?
Yes. Fannie Mae Selling Guide B3-3.1-08 (updated 2023) recognizes ADU rental income for qualification, with lease and security deposit documentation. Freddie Mac, FHA, and (in limited form) VA also recognize it. Up to 30% of qualifying income can come from ADU rental, with higher allowances on specific products.
What's the difference between an ADU and a JADU?
ADUs can be detached or attached, up to 1,200 sqft detached or 50% of primary up to 1,200 sqft attached, no owner-occupancy required, and are subject to Gov Code 65852.2. JADUs are within the existing single-family footprint, up to 500 sqft, owner-occupancy required, and are subject to Gov Code 65852.22.
How long does ADU permitting take?
Gov Code 65852.2(b) mandates a 60-day ministerial review from submittal of a complete application. Simi Valley, Thousand Oaks, and Moorpark all process within the 60-day window on standard plans. Hillside Ordinance review in Thousand Oaks can add 30-60 days; HOA architectural review can add 30-90.
Will an ADU increase my property tax?
Only the ADU's added assessed value is reassessed; the primary residence retains its Prop 13 base. The added assessed value reflects the ADU's construction value (not necessarily its full market value). Expect roughly 1.1-1.25% of construction cost per year in added property tax.
