Folsom | ADUs and SB 9

Folsom, California ADUs and SB 9: the 2026 Accessory Dwelling Unit Chapter, Sizes, Heights, Setbacks, Parking, Fees and Design Standards, and SB 9 Two-Unit Projects

This page covers the two ways state law adds homes to a Folsom house lot: accessory dwelling units and SB 9. An accessory dwelling unit, or ADU, is a second home on a lot that has or will have a main home. A junior ADU is a unit of 500 square feet or less inside a house. Folsom rewrote its ADU rules in 2026: Ordinance No. 1361 repealed and re-enacted Chapter 17.105, and the City Council agenda of April 14, 2026 lists it for second reading and adoption. The new chapter follows the state statutes closely and says that "Where conflict occurs between the regulations of this section and the Government Code, the Government Code regulations shall apply." Folsom has no SB 9 chapter, so the state statute governs two-unit projects. The Folsom overview has the summary.

A New ADU Chapter in 2026

Ordinance 1110 added Chapter 17.105 on second dwelling units, and Ordinance 1306 of 2020 replaced it with an ADU chapter. The disposition of ordinances table, the code host's list of every ordinance, shows that Ordinance 1361 "Repeals and replaces Ch. 17.105, accessory dwelling units." Every section of the chapter now ends with the note "(Ord. 1361 § 2, 2026)."

• March 10, 2026. The City Council agenda listed Ordinance No. 1361 for "Introduction and First Reading" at a public hearing, marked "to be continued to March 24, 2026."
• March 24, 2026. The agenda listed the "Zoning Code Update - Accessory Dwelling Unit Ordinance Hearing" with Ordinance No. 1361, "continued from March 10, 2026."
• April 14, 2026. The consent calendar listed Ordinance No. 1361 for "Second Reading and Adoption." The code host later added it to the code, which is current through Ordinance 1369.

The chapter names state law as its frame. Its purpose is to regulate ADUs "in conformance with California Government Code Title 7, Division 1, Chapter 13," which holds the state ADU statutes. Several sections repeat the statute word for word and add that the Government Code controls where they differ. One term needs explaining: the chapter calls each ADU the state requires a city to approve a "66323 unit," after Government Code 66323. Those units skip the City's design standards and design review.

The City Text Beside State Law

Sources: Folsom Municipal Code 17.105; Government Code 66311.5, 66313, 66314, 66315, 66317, 66321, 66322, 66323 and 66333.

The City column matches the state column in every row but one: the height of a detached ADU that is larger than 800 square feet, covered in the section on differences below.

ADUs on a House Lot

Section 17.105.120 allows, on a single-unit lot, "One attached or detached accessory dwelling unit that complies with the requirements of this chapter"; one ADU inside the house or an existing accessory building; "One junior accessory dwelling unit"; and "One new construction detached accessory dwelling unit consistent with Government Code Section 66323 (a)(2)." The last three are the units Government Code 66323 requires a city to approve; the first is the City's own allowance under the chapter's standards. Ask the Planning Division which combinations it approves on one lot.

• The state-mandated detached unit. A new detached ADU qualifies as a 66323 unit if it is no larger than "eight hundred square feet," has "side and rear setbacks of four feet," and meets the state height. It is approved by staff with no design standards.
• Other detached ADUs. A larger detached ADU may be 850 square feet "if it has no more than one bedroom or one thousand square feet if it has two or more bedrooms." It must not "break the front plane of the primary dwelling unit," must sit "at least six feet from the primary dwelling unit," and may cover no more than forty percent of the rear yard.
• Attached ADUs. An attached ADU follows the same 850 and 1,000 square foot limits, and "the total floor area of an attached accessory dwelling unit shall not exceed fifty percent of the existing primary dwelling unit." Its height may not exceed the zone limit, and any part inside the house setback is limited to twenty-five feet.
• Conversions. An ADU made from space inside the house or an existing accessory building may add "not more than one hundred fifty square feet" for an entrance, and keeps the existing setbacks and height.
• Minimum size. Every ADU must meet "the requirements of an efficiency unit (one hundred fifty square feet minimum)."
• Entrance. The entrance of a non-mandated ADU "shall be located on a different side of the building from the entrance to the primary dwelling unit," unless building codes require otherwise.
• A floor for every lot. "In no event shall any of the standards of this section preclude the development of at least an eight-hundred-square-foot accessory dwelling unit with four-foot side and rear setbacks."

Junior ADUs and Multifamily Lots

• Junior ADU. A junior ADU is "no more than five hundred square feet in size and contained entirely within a single-unit dwelling." It needs an efficiency kitchen, which the chapter defines as a cooking facility with appliances, a food preparation counter and storage cabinets, and its own exterior entrance.
• Deed restriction. Before a building permit, the owner records a deed restriction saying the junior ADU "shall not be sold separately from the primary dwelling unit."
• Owner occupancy. "All junior accessory dwelling units that have shared sanitation facilities shall be subject to an owner occupancy requirement." The rule does not apply when the junior ADU has its own bathroom, matching Government Code 66333 as amended effective January 1, 2026.
• Conversions in apartment buildings. Space "not used as livable space, including but not limited to storage rooms, boiler rooms, passageways, attics, basements, or garages" may become ADUs, up to "twenty-five percent of the original number of approved primary units," with fractions rounded up.
• Detached ADUs on multifamily lots. The chapter allows "Up to two detached accessory dwelling units on a lot that has proposed multi-unit dwellings, or up to eight detached accessory dwelling units on a lot that has existing multi-unit dwellings," and no more than the existing units. Each may be 800 square feet with 4-foot setbacks, and no design standards apply.

Parking, Fees, Renting and Selling

• Parking. "One additional off-street parking space shall be required per accessory dwelling unit or per bedroom, whichever is less." It may sit on a driveway in a setback, as tandem parking (one car behind another) or on a lift in an enclosed garage.
• No parking in six cases. Within "one-half mile walking distance of public transit"; "within the historic district"; for an ADU inside the house or an existing accessory building; where on-street permits are required but not offered; within one block of a car share vehicle; and when the ADU is applied for with a new home on the lot.
• Garage conversions. When a garage, carport or parking space is removed for an ADU, "replacement parking is not required."
• Impact fees. "No city-imposed impact fees shall be charged to an accessory dwelling unit that is seven hundred fifty square feet or less in floor area." A larger ADU pays in proportion to the main home: the ADU floor area divided by the main home floor area, times the fee for a new home.
• Utility charges. An ADU is not a new residential use for water and sewer connection fees "unless the accessory dwelling unit was constructed with a new single-unit dwelling," and the City may not require a separate utility connection unless the utility provider does.
• Renting. An ADU or junior ADU may be rented, but "the rental shall be for a term of thirty days or longer," and no one may live in it until the City approves occupancy of the main home.
• Selling. An ADU "may be sold or conveyed separately from the primary dwelling unit to a qualified buyer, as defined in Government Code Section 66341," when that statute's conditions are met.
• Addresses. "An accessory dwelling unit shall have its own address according to the city's standard addressing procedure."

Design Standards and Review

An ADU that is not a 66323 unit must meet the objective design standards in Section 17.105.190, checked by the community development director in a ministerial review, a staff check against written rules with no hearing. The standards are short:

• Walls. An attached ADU uses "the same exterior wall materials" as the house. A detached ADU uses "at least two different exterior wall materials."
• Windows. A second-story window within ten feet of a side or rear line needs translucent glass or must be a transom, clerestory or false window.
• Roof. The ADU roof matches the house pitch, plus or minus 2/12, a measure of roof slope.
• Two-story ADUs. They need wall offsets, cantilevers or two roof forms; an internal or screened staircase; and at most "One second-story balcony," no larger than twenty square feet.
• Waivers. An owner may ask to depart from a standard through regular design review.

In the historic district an ADU also follows Section 17.105.200, which lists the architectural styles allowed in each subarea, from Queen Anne and Craftsman to 1950s Ranch. Section 17.52.300 gives the Historic District Commission final authority over the design of ADUs that are "not exempt from design review by California Government Code Section 66321 based on height." See the historic district page.

Review Times and Appeals

• Completeness. "Within fifteen business days after the city receives an application, the city shall provide written notice whether the application is complete or incomplete," with a list of missing items. If it does not, the application is deemed complete.
• Decision. A complete ADU or junior ADU application "shall be approved or denied within sixty days," unless it is filed together with a new main home or the applicant asks for a delay.
• Denial. A denial comes with "a full set of comments" listing what to fix, within the same sixty days.
• Appeals. An applicant may appeal to the Planning Commission, which decides "within sixty business days after receipt of the appeal." The commission's decision "is final and may not be further appealed."
• Building permit. Every ADU and junior ADU needs a building permit, "subject to all the standard application and processing fees."

SB 9: Two Homes on a Single-Family Lot

SB 9 has two parts. Government Code 65852.21 requires a city to approve "A proposed housing development containing no more than two residential units within a single-family residential zone" without a hearing, and Section 66411.7 allows the lot to be split. Both were amended effective June 30, 2026. Title 17 has no SB 9 chapter, and its contents list none. The statute applies to Folsom directly, because it defines a local agency as a city "whether general law or chartered."

Source: Government Code 65852.21, effective June 30, 2026.

• Which zone. Section 17.10.010 lists "R-1-L, R-1-ML, R-1-M, single-family residence districts." Those are the zones where SB 9 applies on its face; ask the City how it treats a lot in a planned development or a specific plan zone.
• ADUs with SB 9. On a parcel made by an SB 9 lot split, Section 17.105.120 allows "no more than two units (including ADUs and JADUs)."
• Standards. A city may apply objective zoning and design standards, except ones that would block two units or a unit of 800 square feet. The R-1 coverage, yard and height rules are on the parking, setbacks and height page; under the statute, side and rear setbacks may not exceed four feet.
• Historic district. The statute excludes "A contributing structure within a historic district" listed under a city ordinance. Folsom's historic district is created by Chapter 17.52.

Where the City Text and State Law Differ

• Detached ADU height. For a detached ADU that is not a 66323 unit, "Height shall not exceed twenty-five feet or the height of the residence, whichever is less." Government Code 66321 bars any limit that does not allow "A height of 16 feet for a detached accessory dwelling unit." On a lot whose house is lower than 16 feet, the statute controls.
• ADUs in mixed-use zones. Table 17.23.030 marks "Second dwelling units" as "N" in the MU zones, while Section 17.105.010 allows ADUs on parcels zoned for multi-unit homes. The 2026 chapter and Government Code 66314 control.
• Garage conversions. Section 17.57.030 says no "garage conversion to nonvehicular use" may be made on a residential lot with substandard parking unless the covered spaces are provided. Section 17.105.180 and Government Code 66314 say replacement parking is not required when a garage becomes an ADU. The ADU rules control for an ADU.
• Historic district text. Section 17.52.500 applies the design standards to ADUs "larger than eight hundred square feet or taller than sixteen feet," while Section 17.105.110 applies them to every ADU that is not a 66323 unit. Section 17.52.540 also says that in The Preserve subarea "successful design of a second unit is unlikely." Government Code 66323 requires approval of a qualifying unit regardless.
• Old section numbers. Section 16.04.050 still cites "Section 65852.2 of the Government Code," the ADU section number used before SB 477 of 2024.

Limits of This Page

The City website answered 403, so the City's ADU handouts, pre-approved plans, application forms and fee schedule were not read, and the staff report for Ordinance 1361 was not read; the agendas say staff reports are on the City website. No ADU or SB 9 application fee is given here. City Council agendas through October 13, 2026 list no later ADU ordinance. Ask the Planning Division which forms apply and whether anything has changed since.

Where to Go Next

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

Frequently Asked Questions

Official sources (checked October 2026)