Simi Valley | ADUs and SB 9

Simi Valley ADUs and SB 9: ADU Sizes, the 2025 HCD Findings, Two-Unit Developments and Lot Splits

Simi Valley offers two ways to add homes to a house lot without a rezoning. An accessory dwelling unit (ADU) is a second home on the lot with its own kitchen and bathroom; a junior ADU is a smaller unit inside the main house. Section 9-44.160 of the Development Code holds the ADU rules. SB 9 lets an owner build two main homes on one lot, split the lot in two, or both; Simi Valley calls these a Two-Unit Residential Development and an Urban Lot Split, in Section 9-24.080. In October 2025 the state housing department found the ADU rules out of step with state law, so this page sets out the code and the points where state law controls. The Simi Valley overview has the summary.

ADU Sizes and Standards

Source: Simi Valley Municipal Code Sec. 9-44.160, Tables 4-4, 4-5 and 4-7 and Subsections A, E and F. Where state law sets a different floor, it controls; see below.

Section 9-44.160 applies to lots zoned OS, RE, RVL, RL, RM, RMod, RH, MH and RVH and to the Mixed-Use Overlay. An ADU or junior ADU "shall not count towards the allowable density for the lot." Each one needs a Zoning Clearance, a staff check that the plans meet the code, reviewed "ministerially," which means by staff against fixed rules with no hearing. The section also keeps a broad power: "The City reserves the right to limit construction of ADUs or JADUs in locations where there is inadequate water or sewer services, impact on traffic flow, or public safety."

• Lot combinations. Table 4-4 allows a house lot "One JADU and/or one ADU." If both are built, "the ADU must be detached and is limited to 800 square feet in size."
• Attached ADUs must share at least 10 feet of wall with the house or SB 9 home, with no internal connection. An ADU made from existing living space inside the house has no size cap, plus up to 150 square feet of addition for an entrance.
• Detached ADUs may not connect to the house by a breezeway and must stand at least six feet from other buildings. The first detached ADU of up to 800 square feet follows only the general standards in Table 4-5. A larger one also meets Table 4-6: a 20 foot front setback, no more than 40 percent coverage of the first 10 feet of a side yard and the first 20 feet of the rear yard, and half of the rear yard width left open.
• Garages and patios. A detached ADU may attach to a garage of up to 400 square feet and a patio cover of up to 10 percent of the ADU's floor area.
• Windows. No window may sit above the first 10 vertical feet of a wall, and a second-story attached ADU without 10 foot side and 20 foot rear setbacks may have no windows facing neighbors.
• Entrances. Each ADU or junior ADU needs its own entrance, which "shall not face the street" unless the building code access is blocked by an existing permitted structure.
• Junior ADUs. Before the Zoning Clearance, the owner records a deed restriction requiring the owner to live in the junior ADU or the main home. If a new owner does not, the junior ADU must be removed and any separate rental vacated within 90 days.
• Rentals of an ADU, a junior ADU, or the main home when the owner lives in the ADU must be for 30 days or more.

Every ADU on land under the Hillside Performance Standards "will be limited to 800 square feet in size," and its driveway follows Chapter 9-32. When a new house and an ADU are built together, the house must be approved for occupancy before the ADU.

The 2025 HCD Findings

The California Department of Housing and Community Development (HCD) reviews city ADU ordinances. On October 29, 2025 it wrote to the City that ADU Ordinance No. 1349, adopted June 5, 2023, "fails to comply with State ADU Laws." The letter lists 19 findings and gave the City until November 28, 2025 to respond in writing. The City could amend the ordinance or adopt findings explaining why it believes the ordinance complies. Supplement 52 of the code, current through March 9, 2026, still prints the Ordinance No. 1349 text. VanPlex could not read any City Council action after that date, so ask the Planning Division whether a newer ADU ordinance is in force before you design. The findings that change what an owner can build:

• Old statute numbers. The section cites Government Code 65852.2 and 65852.22, which were "deleted by SB 477, effective March 25, 2024" and moved to Sections 66310 to 66342.
• Apartment lots. The code limits a multi-family lot to attached ADUs up to 25 percent of the units or two detached ADUs. State law allows conversion ADUs in non-living space and, on a lot with an existing multifamily dwelling, "up to eight detached ADUs, not to exceed the number of existing units on the lot," and allows both kinds on one lot.
• Garages counted as living area. The code's definition of "living area" includes garages. HCD quoted Government Code 66313: "Living area means the interior habitable area of a dwelling unit, including basements and attics, but does not include a garage or any accessory structure."
• Decision deadline. The code says the City "shall act on" an application in 60 days. HCD said the City must approve or deny it in that time, and deny with "a full set of comments."
• Parking. The exemptions omit ADUs in "an architecturally and historically significant historic district" and ADUs applied for together with a new house or apartment building.
• Six-foot separation and the 20 foot front setback and coverage limits in Table 4-6 may not be applied to the ADUs that Government Code 66323 requires a city to approve, and may not block an 800 square foot ADU with four-foot side and rear setbacks.
• Size caps on apartment-lot ADUs. The 800 square foot cap does not apply to detached ADUs built under Government Code 66323(a)(4).
• Unpermitted structures may be converted to ADUs unless they threaten health and safety and are affected by the work.

This guide could not read any City response or later ordinance, because the City's website refused automated requests and Municode's ordinance bank lists no Simi Valley ordinances. Until a new ordinance is adopted, read Section 9-44.160 together with the state rules. Where a Simi Valley rule is stricter than the state floor in Government Code 66314 to 66342, the state floor controls.

State Floors That Control

• Size. Government Code 66321(b)(2) bars a maximum ADU size below "Eight hundred fifty square feet" or "One thousand square feet of interior livable space for an accessory dwelling unit that provides more than one bedroom." The 800 square foot hillside cap and the 800 square foot cap on apartment-lot ADUs in Table 4-7 fall below that floor.
• Height. Government Code 66321(b)(4) requires at least 16 feet for a detached ADU, 18 feet near transit or on a lot with a multistory multifamily building, and 25 feet or the zone limit for an attached ADU. Simi Valley's 18 foot detached limit meets the floor.
• Deadline. Government Code 66317 requires a decision on a complete application "within 60 days" when a home already exists on the lot.
• Fees. Government Code 66311.5 bars impact fees on an ADU of 750 square feet or less and a junior ADU of 500 square feet or less.

ADUs and junior ADUs are also exempt from the City's yearly building permit allocation system, under the Class 1 exemption in Section 9-36.020. The California ADU law page explains the state rules in full.

SB 9 Two-Unit Developments

Source: Simi Valley Municipal Code Sec. 9-24.080, Table 3-2 and Subsections J, K, L and N. Table 3-2 lists the RVL, RL, RM and RMod-Single districts.

Section 9-24.080 says it provides "objective standards for Two-Unit Residential Development, pursuant to California Government Code Sections 65852.21 and 66411.7." The Director approves a qualifying project "with a Zoning Clearance," and the City "shall ministerially approve or disapprove a complete building permit application." Waivers and variances are not allowed. The units may be attached as a duplex or detached. Each may be rented separately, but for no less than 31 days. Unit size depends on the parcel: 800 square feet up to 5,000, 1,000 up to 8,000, 1,200 up to 20,000, and 2,000 above. A primary home built before December 31, 2021 may be expanded past those sizes.

The section bars SB 9 projects in these cases:

• Housing with an affordability covenant, rent or price control, or "a tenant in the last three years."
• A parcel withdrawn from the rental market under the Ellis Act (Government Code 7060) within 15 years.
• Demolition of more than 25 percent of the exterior walls, unless no tenant has lived there in the last three years.
• Very High Fire Hazard Zones, unless the buildings meet the high fire construction standards, with "No variance or modification" to the fire codes.
• The Alquist Priolo Fault Zone, the 100 year flood zone, the Habitat Connectivity and Wildlife Corridor, prime farmland, wetlands or a hazardous waste site, "unless proper mitigations are approved."
• Property on the State Historic Resources Inventory, a County Landmark or Structure of Merit, or a historic property listed in the General Plan.

Each new primary home needs its own one-car garage, at least 12 feet wide inside under Section 9-34.080, unless the lot is within one-half mile walking distance of a high-quality transit corridor or major transit stop, or a car share vehicle is within one block. A converted garage must be replaced by a new garage. Each primary home needs 200 square feet of open space outside the setbacks. On "parcels outside the valley floor," homes are "limited to 800 square feet in size" and follow the hillside chapter.

Urban Lot Splits

An Urban Lot Split divides a lot "to create no more than two new parcels," each with "gross lot area" of at least 1,200 square feet, and "No parcel may be less than 40 percent of the original lot size." The new lots do not have to meet the zone's minimum width. The owner files a Tentative Parcel Map under Chapter 9-61, and Table 6-1 names the Director as the decision maker and lists no appeal to the Commission or Council. The City may not require street dedications or off-site improvements. A lot already split under SB 9 cannot be split again, and an owner who split an adjacent lot cannot split another. Lots on slopes of 20 percent or more follow the hillside chapter. The lot size and subdivisions page covers the map steps.

Where the Code and State Law Differ

• Two-story setbacks. Table 3-2 asks 10 foot side and 20 foot rear setbacks for two-story SB 9 homes. Government Code 65852.21 and 66411.7 say a city "may require a setback of up to four feet from the side and rear lot lines." The statutes control.
• Owner occupancy on a lot split. Section 9-24.080.O.7 requires the owner to live in a unit for three years from the recording of the parcel map or from the first certificate of occupancy. Government Code 66411.7(g) asks only an affidavit of intent to live there "for a minimum of three years from the date of the approval of the urban lot split," and bars "additional owner occupancy standards." The statute controls.
• Junior ADU plus ADU. Table 4-4 lets a house lot combine an ADU and a junior ADU only if the ADU is detached. Government Code 66323(a)(1) requires a city to approve one ADU and one junior ADU within the space of a house. The statute controls.
• Zoning Clearance for ADUs. Government Code 66321(b)(3) bars "any requirement for a zoning clearance or separate zoning review" that does not permit an 800 square foot ADU with four-foot side and rear setbacks.
• Table numbers. Section 9-24.080 calls its SB 9 setback table "Table 3-2," and Section 9-30.080 has a different Table 3-2 for accessory structures.

Where to Go Next

Related on VanPlex: the Simi Valley overview, the California ADU law page and the SB 9 page.

Frequently Asked Questions

Official sources (checked October 2026)