ADUs in Simi Valley: City Rules, Value and Selling a Home

Can you build an ADU in Simi Valley? Yes. The city allows accessory dwelling units (ADUs) and junior ADUs (JADUs) on residentially zoned lots with a home, without a public hearing. A new detached ADU can be up to 1,000 square feet on a lot up to 8,000 square feet, or 1,200 square feet on a larger lot, with a lower limit on hillside lots. In most cases you can't sell the ADU apart from the house, so its value shows up when you sell the whole property, and that value depends a lot on whether the unit was permitted.

We're Steve Hise and Tricia Garcia, and we help homeowners across Simi Valley buy and sell. One caution first: the city says its ADU ordinance is being updated. The numbers below come from the current municipal code and the state's March 2026 ADU Handbook, so confirm them with Simi Valley Planning at (805) 583-6769 before you pay for plans.

1. ADU or JADU: what's the difference?

An ADU is a complete, independent home on the same lot as a main house. It can be attached, detached, or converted from existing space such as a garage. A JADU is no more than 500 square feet, sits entirely inside the main home, and may have its own bathroom or share one.

2. Simi Valley's ADU rules at a glance

From Simi Valley Municipal Code Section 9-44.160, last amended in 2023 according to the online code:

Rule	Attached ADU	Detached ADU	JADU
Maximum size	Half the existing home or 800 sq. ft., whichever is larger, up to 1,000 sq. ft.	1,000 sq. ft. on lots up to 8,000 sq. ft.; 1,200 sq. ft. on larger lots	500 sq. ft., inside the home
Height	25 ft. or the zone's limit, if lower (up to 30 ft. with larger setbacks)	One story, 18 ft.	Not on a second floor
Side and rear setbacks	4 ft.	4 ft., plus 6 ft. from other structures	Not applicable

A few other rules catch people off guard:

• Hillside lots: ADUs on slopes under the city's Hillside Performance Standards are limited to 800 square feet.
• ADU plus JADU: A single-family lot can have both, but the ADU must then be detached and no larger than 800 square feet.
• Over 800 square feet: New construction must also meet a 20-foot front setback and yard coverage limits.
• Conversions: Existing living area can become an ADU with no size cap if it stays within the existing structure.
• Parking: One space, with exceptions that include studios, units within a half-mile walk of public transit, and garage conversions.
• Entrance: Each unit needs its own entrance, which generally can't face the street.

3. The state rules on top of city code

• Timing: The agency must say whether an application is complete within 15 business days, and approve or deny a complete application within 60 days when a home already exists on the lot.
• Impact fees: None on an ADU with 750 square feet of interior livable space or less. Above that, they're charged in proportion to the main home's size. Other district fees can apply above 500 square feet, so ask for a full fee estimate.
• Owner-occupancy: Cities generally can't require it for an ADU. For a JADU, it applies when the unit shares a bathroom with the main home, and not when it has its own.
• Rentals: No short-term rentals. In Simi Valley, the term must be 30 days or more, and fair housing laws apply.

Simi Valley's current code still requires a recorded deed restriction on JADUs. It says that if a new owner doesn't keep up the required owner-occupancy, the JADU must be removed and any separate rental vacated within 90 days. State law has changed since that code was last amended, so ask Planning how this applies. If you're buying a home with a JADU, read what was recorded before you remove contingencies.

4. If you live in an HOA

Under Civil Code Sections 714.3 and 4751, CC&Rs can't effectively prohibit or unreasonably restrict an ADU or JADU on a lot zoned for single-family use. An HOA can still set limited objective standards, such as reasonable design and material rules, but those can't include fees or other financial requirements.

5. Does an ADU add value?

It can, but there's no fixed number, and what you paid to build isn't the same as market value. Here's how value gets measured:

• The appraisal. Under Fannie Mae's Selling Guide, an ADU is generally reported on its own line, not added to the main home's square footage, and the appraiser must analyze its effect on value or marketability.
• The definition. Fannie Mae looks for a separate way in and out, a kitchen, a sleeping area and a bathroom, in a unit smaller than the main home. A second kitchen alone isn't an ADU.
• Rent for the next buyer. Fannie Mae allows rent from one existing ADU to help a buyer qualify on a purchase, capped at 30% of total qualifying income. Other loan programs differ.
• Property taxes. The Board of Equalization says additions are generally assessable new construction, which may raise your bill. See our guide to Simi Valley property taxes.
• Insurance. Get a quote that includes the unit first. See our Simi Valley home insurance guide.

6. Selling a Simi Valley home with an ADU

You generally sell it with the house. HCD says a city may adopt an ordinance allowing separate sale as condominiums, with a narrow exception for certain nonprofit-built units. Simi Valley's ADU section doesn't include that option.

Pull your paperwork early. Gather permits, the final inspection sign-off, any recorded deed restriction, and the lease if it's rented.

Be upfront about anything unpermitted. A city can't deny a permit for an unpermitted ADU built before January 1, 2020, just because it breaks building standards or ADU rules, unless it finds a correction is needed to protect the public or occupants, or the building is substandard. Either way, disclose what you know. See our guide to California seller disclosures.

Price it with real comparisons. Look for sales with a similar unit. Our post on pricing a Simi Valley home walks through the method.

7. Nearby cities have their own rules

State law applies everywhere, but Moorpark, Thousand Oaks, Camarillo and the City of Los Angeles each set local standards within it. If you're comparing homes across city lines, as in our Simi Valley vs. Moorpark guide, ask each planning office about the specific address.

Frequently Asked Questions

How big can a detached ADU be in Simi Valley?
Up to 1,000 square feet on lots up to 8,000 square feet, and 1,200 square feet on larger lots. Hillside lots are limited to 800 square feet.

Can I sell my ADU separately from my house?
Generally no. That takes a local ordinance under Government Code Section 66342, and Simi Valley's ADU section doesn't include one.

Do I have to live on the property if I have an ADU?
Generally no. A JADU that shares a bathroom with the main home is different: the owner must live on the property.

Can my HOA stop me from building an ADU?
Not outright. An HOA can apply limited, objective design standards, but it can't effectively prohibit or unreasonably restrict an ADU on a single-family lot.

Thinking about an ADU, or selling a home that has one?

Tell us about your property and we'll help you think it through. Schedule a call, or call or text 805-424-6226. Curious what your place is worth? Start with What's My Simi Valley Home Worth?

Sources

All checked November 5, 2026.

• City of Simi Valley: Planning Division
• Simi Valley Municipal Code Section 9-44.160
• California HCD: ADU Handbook, March 2026 (PDF)
• State Board of Equalization: New Construction
• Fannie Mae Selling Guide B2-3-04
• Fannie Mae Selling Guide B4-1.3-05
• Fannie Mae Selling Guide B3-3.8-02

Steve Hise and Tricia Garcia, Real Estate Toolbox at eXp Realty, 1720 E Los Angeles Ave, Suite F, Simi Valley, CA 93065
Steve Hise CA DRE #01702055 | Tricia Garcia CA DRE #02032007

This article is general information, not legal, tax, or financial advice. ADU laws and city standards change; confirm the rules for your property with the City of Simi Valley Planning Division and your own advisors.