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Building an ADU in Simi Valley

City code and California law · Last reviewed October 10, 2026

Simi Valley allows ADUs and junior ADUs on residential lots under Municipal Code section 9-44.160, last rewritten in 2023. A detached ADU can be up to 1,000 sq ft on lots up to 8,000 sq ft and 1,200 sq ft on larger lots, one story and 18 feet tall, with 4-foot side and rear setbacks. The city says its ADU rules are being updated, and in October 2025 the state housing agency (HCD) found 19 ways the 2023 ordinance falls short of state law. Where they differ, the state rules on our California page set the floor, so check any limit with the Planning Division before you design. [1][2][3][4]

Simi Valley at a glance

Which rules apply
SVMC 9-44.160 (last amended by Ord. No. 1349, effective July 5, 2023) The city says an update is under way, and HCD found the 2023 ordinance out of step with state law in October 2025 [1][2][3]
Number on a single-family lot
City code: one ADU and/or one JADU (if both, the ADU must be detached and 800 sq ft max). State law: one converted ADU, one new detached ADU and one JADU must be allowed [1][4]
Detached ADU size
1,000 sq ft on lots up to 8,000 sq ft 1,200 sq ft on larger lots; 800 sq ft with a JADU, with an SB 9 project, or on hillside slopes [1][5]
Attached ADU size
50% of the house or 800 sq ft, whichever is larger, up to 1,000 sq ft Converting existing living space has no size limit [1]
Junior ADU
Up to 500 sq ft inside the existing house Not on a second floor [1]
Height
Detached: one story, 18 ft (20 ft near major transit to match roof pitch). Attached: 25 ft or the zone limit, up to 30 ft with larger setbacks [1]
Setbacks
4 ft side and rear 6 ft from other buildings for a detached ADU; 20-ft front setback for new ADUs over 800 sq ft [1][5]
Parking
1 space per ADU, with exceptions (studios, near transit, inside the house, garage conversions and others) None for a JADU [1]
Owner occupancy
None for an ADU. City code requires it for every JADU State law since 2026 requires it only if the JADU shares a bathroom [1][4]
Building plan check and inspection fee
From $3,109 for a 500 sq ft ADU Lowest construction-type column, fees effective July 1, 2025 [6]
Approval deadline
State law: completeness notice within 15 business days Approve or deny within 60 days of a complete application [3][4]
Short-term rental
No: an ADU or JADU must be rented for 30 days or more [1][5]
On this page
  1. At a glance
  2. Which rules apply in Simi Valley
  3. What HCD told Simi Valley in 2025
  4. Size, height and setbacks
  5. Parking
  6. Fees
  7. How long it takes
  8. Garage conversions and junior ADUs
  9. SB 9 lots and multifamily properties
  10. Renting it out
  11. Permit steps
  12. Who to call
  13. Questions people ask

Which rules apply in Simi Valley

Simi Valley's ADU rules are in section 9-44.160 of the Simi Valley Municipal Code. The section was last amended by Ordinance No. 1349, effective July 5, 2023. ADUs and JADUs are allowed on lots with an existing or proposed home in the OS, RE, RVL, RL, RM, RMod, RH, MH and RVH zones and the Mixed Use overlay. Each one needs a Zoning Clearance, which the code says is "ministerially reviewed," plus a building permit.

The city's Planning Division page says the "Accessory Dwelling Unit Ordinance and development standards are currently undergoing updates." It points to the code section and to the city's ADU Guide (July 2023), a plain-language summary of the same rules.

In an October 29, 2025 findings letter, HCD reviewed Ordinance No. 1349 and found it "fails to comply with State ADU Laws." The next section lists the main points. State law generally overrides a stricter local rule, so where this page says "the city says X; state law says Y," plan around state law and confirm with Planning at (805) 583-6769. [1][2][3][5]

What HCD told Simi Valley in 2025

HCD's letter listed 19 findings. The ones most likely to affect a homeowner:

HCD gave the city until November 28, 2025 to respond. The city's online code, updated through an ordinance that took effect April 8, 2026, still shows the 2023 ADU text.

One more difference is not in the letter. The city's table allows one JADU and/or one ADU on a single-family lot, and if you build both, the ADU must be detached and no larger than 800 sq ft. HCD's 2026 handbook says cities "must allow at least one ADU constructed from existing space, one JADU, and one newly constructed detached ADU" on single-family lots. Confirm with Planning if you want more than one unit. [1][2][3][4][5]

Size, height and setbacks

The city's limits, from the code and the ADU Guide:

State law sets a floor under these rules. A city's maximum size can't be less than 850 sq ft, or 1,000 sq ft for an ADU with more than one bedroom, and a percentage-of-house limit can't push an attached ADU below those sizes. Front setbacks, lot coverage and similar limits can't block an 800 sq ft ADU with 4-foot side and rear setbacks. HCD's handbook also says a city can't deny a two-story detached ADU that fits within the state height allowances and building code. Ask Planning how the city's one-story rule and 1,000 sq ft attached cap apply to your lot. [1][3][4][5]

Parking

The code requires one parking space per ADU, which can be uncovered or tandem on a paved driveway. No space is needed when:

The code also lets the Director waive the space if there is no feasible place for it. A JADU needs no extra parking.

State law adds two more exemptions the city's list leaves out: ADUs in an architecturally and historically significant historic district, and ADUs applied for together with a new home on the same lot when the ADU or the lot also meets one of the other exemptions. It also bars parking requirements for the state's by-right ADUs and says a city can't make you replace parking lost when a garage or carport is converted or torn down for an ADU. [1][3][4][5]

Fees

City fees. The city's Summary of Service Charges (effective July 1, 2025) lists a Zoning Clearance at $120.43 (minor) or $1,421.02 (major); ask Planning which applies. For building plan check and inspection, the "Accessory Dwelling Unit" row starts at $3,109 for 500 sq ft plus $111.80 per extra 100 sq ft, and $3,668 at 1,000 sq ft, in the lowest construction-type column (III-B, IV, V-B). The schedule also lists an 8% trade permit and plan check surcharge each for plumbing, mechanical and electrical work.

Other agencies. The ADU Guide lists approvals and fees from outside departments:

State limits. Under state law, an ADU of 750 sq ft of interior livable space or less pays no impact fees, and a larger one pays only in proportion to the house. School districts can charge only ADUs over 500 sq ft. For typical costs see our ADU cost guide. [4][5][6]

How long it takes

The city's code says it will act on an application within 60 days of the date it is deemed complete when a home already exists on the lot. If you apply for an ADU together with a new house, the city may wait to act on the ADU until the house's building permit is issued, and the house must be approved for occupancy before the ADU is.

State law is stricter on the city: it must tell you in writing within 15 business days whether your application is complete, and approve or deny a complete application within 60 days. A denial must include a full list of what is wrong and how to fix it. HCD told Simi Valley in 2025 to change "act on" to "approve or deny." More in our ADU permit process guide. [1][3][4]

Garage conversions and junior ADUs

Garage conversions. Converting a garage that provides your required parking doesn't trigger a new parking space for the ADU. If you convert only part of an attached garage, the rest must stay parking if it is at least 12 by 20 feet, or otherwise be used for storage or another non-living use. A legally permitted detached garage or other accessory structure can be converted in place with no size or height limit and no extra setbacks, plus up to 150 sq ft for entry and exit. The code still requires 6 feet of separation from other buildings for a detached ADU, a rule HCD said can't apply to the state's by-right ADUs. See our garage conversion guide.

Junior ADUs. A JADU can be up to 500 sq ft inside the existing house, with at least an efficiency kitchen. It may share a bathroom with the house; if it does, it needs an internal connection to the house. JADUs aren't allowed on a second floor. Before the Zoning Clearance is issued, the city requires a recorded deed restriction saying the owner will live in the JADU or the house.

State law changed in 2026: owner occupancy can be required only if the JADU shares a bathroom with the house, and a JADU deed restriction may cover only the ban on separate sale and the JADU's size and features. If your JADU has its own bathroom, ask Planning about the deed restriction form. See our junior ADU guide. [1][3][4][5]

SB 9 lots and multifamily properties

SB 9. The city adopted Ordinance No. 1352, effective December 18, 2023, for two-unit developments and lot splits under SB 9. The ADU code allows an ADU or JADU in place of an SB 9 unit, up to four homes across both lots; those ADUs are limited to 800 sq ft and 18 feet and must be 10 feet from other buildings. No ADUs are allowed when each new lot already has two SB 9 units. The ADU Guide asks SB 9 applicants to contact Planning. See our SB 9 guide.

Apartments and other multifamily lots. The city allows attached ADUs in non-living space of an existing building (storage rooms, garages and similar), up to 25% of the existing units and at least one, or two detached ADUs of up to 800 sq ft each. State law allows up to eight detached ADUs on a lot with an existing multifamily building (not more than the number of existing units), lets you combine them with converted ADUs, and sets no size cap on the state's by-right detached ADUs. HCD told the city to update these rules. [1][2][3][4][5]

Renting it out

An ADU or JADU must be rented for 30 days or more, so short-term rentals are out. The rule also covers the main house if the owner lives in the ADU or JADU. You don't have to live on the property to rent an ADU.

State law requires the city to track all ADUs and JADUs, so it asks owners to fill out its ADU Occupancy and Rents Survey, and it reminds landlords to follow fair housing laws. Selling an ADU separately from the house is possible in California only in limited cases, such as where a city adopts a condominium ordinance; ask Planning before you plan on it. [1][2][4][5]

Permit steps in Simi Valley

  1. Check your lot

    Check whether your property is in a flood zone; if it is, call Public Works at (805) 583-6786 about building limits. Check the zone and any hillside slopes on your lot. [1][5]

  2. Talk to the Planning Division

    Call Planning at (805) 583-6769 or email Enviroservices@simivalley.org about setbacks, size and parking. You can send an initial site plan, even hand drawn with dimensions, for feedback. [2][5]

  3. Ask Building and Safety what to submit

    Call the Building & Safety counter at (805) 583-6723 to confirm submittal requirements and how to submit on the city's online permit portal. [5][7]

  4. Prepare plans

    You need a dimensioned site plan, existing and proposed floor plans, elevations showing finishes and roof slope, and utility connections, plus Title 24 energy calculations and, for new construction, structural plans and calculations. [5]

  5. Get outside clearances

    Depending on the project: a Ventura County Fire Department 610 form, a fire-flow (625) test from your water provider, a Watershed Protection District waiver or receipt, a Sanitation Will-Serve letter, and a school district receipt for ADUs over 500 sq ft. [5]

  6. Zoning Clearance, plan check and permit

    The city approves a code-compliant ADU through a Zoning Clearance and building plan check. For a JADU, record the city's deed restriction before the Zoning Clearance is issued. Pay plan check and permit fees. [1][5][6]

  7. Build, pass inspections and fill out the survey

    Build to the approved plans and pass inspections. The city asks owners with an ADU to complete its ADU Occupancy and Rents Survey. [2][7]

Who to call

Questions people ask

How big can an ADU be in Simi Valley?

A detached ADU can be up to 1,000 sq ft on lots of 8,000 sq ft or less and 1,200 sq ft on larger lots (800 sq ft if you also build a JADU, on hillside lots, or with SB 9). An attached ADU is capped at 1,000 sq ft. State law says the city must allow at least 850 sq ft, or 1,000 sq ft with more than one bedroom. [1][4]

Can I build both an ADU and a junior ADU in Simi Valley?

The city's code allows both only if the ADU is detached and no larger than 800 sq ft. HCD's 2026 handbook says cities must allow a converted ADU, a new detached ADU of up to 800 sq ft and a JADU on the same single-family lot. Confirm with Planning. [1][3][4]

How tall can a detached ADU be in Simi Valley?

The city limits a detached ADU to one story and 18 feet, or 20 feet within a half-mile of a major transit stop when needed to match the house's roof pitch. HCD's handbook says a city can't deny a two-story detached ADU that fits the state's height allowances, so ask Planning if you want two stories. [1][4]

Do I need parking for an ADU in Simi Valley?

Usually one space, which can be uncovered or tandem on the driveway. None is needed for a studio, an ADU within a half-mile of transit, one inside the house, a garage conversion, and a few other cases. A JADU needs no parking. [1][5]

Can I Airbnb my ADU in Simi Valley?

No. The city's code says any ADU or JADU must be rented for periods of 30 days or more. [1]

Sources (7)
  1. Simi Valley Municipal Code Section 9-44.160, Accessory Dwelling Units (Ministerial) (Supp. No. 52, codified through Ord. No. 1367), City of Simi Valley (via Municode). Accessed October 10, 2026.
  2. Planning Division, City of Simi Valley Department of Environmental Services. Accessed October 10, 2026.
  3. Review of Simi Valley's Accessory Dwelling Unit (ADU) Ordinance under State ADU Law (October 29, 2025), California Department of Housing and Community Development. Accessed October 10, 2026.
  4. Accessory Dwelling Unit Handbook (March 2026), California Department of Housing and Community Development. Accessed October 10, 2026.
  5. Accessory Dwelling Units (ADU Guide, July 2023), City of Simi Valley Department of Environmental Services. Accessed October 10, 2026.
  6. Summary of Service Charges (effective July 1, 2025), City of Simi Valley. Accessed October 10, 2026.
  7. Building & Safety Division, City of Simi Valley Department of Environmental Services. Accessed October 10, 2026.

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