ADU rules in Folsom

Ord. 1361 (adopted 4-14-2026, effective 5-14-2026) repealed and re-enacted FMC Chapter 17.105 and allows ADUs on any parcel zoned for single-unit, two-unit or multi-unit residential use that holds an existing or proposed home (17.105.010(D)). A single-unit lot may carry one local-standards attached or detached ADU, one conversion ADU, one JADU and one new-construction detached state-exempt (Gov. Code 66323) unit of up to 800 sq ft (17.105.120(A)(1)), so up to three ADUs plus a JADU. A local-standards detached unit needs 4-ft side and rear setbacks and 6 ft of separation from other buildings, may not sit forward of the home's front plane and may cover at most 40 percent of the rear yard, but no standard may block an 800 sq ft unit with 4-ft setbacks (17.105.150(B), (C)(2)). Lots with multi-unit buildings may add up to two detached ADUs with a proposed building or up to eight with an existing one, never more than the existing unit count (17.105.120(A)(2)(b), 17.105.170(B)). ADUs are also allowed in the Historic District under the same chapter (17.52.490, 17.52.500), where non-exempt units must follow a historic architectural style.

Attached ADUs that share a structural wall, floor, ceiling or roof with the home, including additions and conversions of space inside the home, are allowed (17.105.030(A)). A conversion of existing or proposed space in a single-unit home, with up to 150 sq ft of expansion for ingress and egress, is a state-exempt 66323 unit with no size cap and no design standards (17.105.090(A), 17.105.140(A)). Other attached ADUs need the zone's front setback, 4-ft side and rear setbacks, an entrance on a different side from the home's, the zone height limit (25 ft for any part inside the home's required setback area) and the objective design standards of 17.105.190 (17.105.140(B)-(C)). A JADU of up to 500 sq ft with an efficiency kitchen and its own exterior entrance may be created inside a single-unit home on single-unit-zoned parcels (17.105.010(D), 17.105.160), and existing multi-unit buildings may convert non-livable space such as storage rooms, attics, basements or garages into ADUs, at least one and up to 25 percent of the original units (17.105.120(A)(2)(a), 17.105.170(A)).

Local-standards ADUs are capped at 850 sq ft with no more than one bedroom and 1,000 sq ft with two or more, measured as interior living space with a 150 sq ft minimum (17.105.140(B)(2), 17.105.150(B)(2)), exactly the Gov. Code 66321(b)(2) floors; an attached unit is further limited to 50 percent of the existing home, but no standard may preclude an 800 sq ft unit with 4-ft side and rear setbacks (17.105.140(C)(2), 17.105.150(C)(2)). The new-construction detached 66323 unit is capped at 800 sq ft with the Gov. Code 66321(b)(4) heights (16 ft, up to 20 ft near major transit with a roof pitch matching the home) (17.105.150(A)(1)), and the code applies the same 800 sq ft cap to every detached ADU on a two-unit or multi-unit lot (17.105.170(B)(2); see caveats). Local-standards detached units may reach 25 ft or the height of the home, whichever is less, except that a unit on or within 50 ft of a parcel with a state- or federally-listed historic structure is held to the 66321 heights (17.105.150(B)(5)); attached units follow the zone height limit, 25 ft where they reach into the home's setback area (17.105.140(B)(5)). Conversions keep the existing envelope plus 150 sq ft for access, and JADUs are capped at 500 sq ft (17.105.160(A)(2)).

Chapter 17.105 imposes no owner-occupancy requirement on any ADU, consistent with Gov. Code 66315. Only a JADU that shares sanitation facilities with the home requires a person with legal or equitable title to live on the property, in the home or the JADU, as a legal domicile; a JADU with its own bathroom, or one owned by a government agency, land trust or nonprofit housing organization, is exempt (17.105.160(B)(4)), mirroring Gov. Code 66333(b) as amended by SB 543 and AB 1154. Every JADU still needs a recorded deed restriction barring separate sale and fixing its size and attributes (17.105.160(B)(3)); the city's template (Form CD-P515) carries the conditional owner-occupancy clause, and the JADU checklist (CD-P215, Revs. 5-14-26) asks for recording before final inspection while the code says before building permit issuance. The 2020 ordinance it replaced was on file with HCD when HCD's 12-5-2025 letter flagged the JADU shared-sanitation change.

Section 17.105.180(A) requires one off-street space per ADU or per bedroom, whichever is less, which may sit on a driveway in the front or side setback, in tandem, or on a lift in an enclosed garage. No space is required within one-half mile walking distance of public transit (defined to include bus stops), anywhere in the Historic District, for a unit that is part of the home (attached ADUs and JADUs) or of an existing accessory building, where on-street permits are not offered to the occupant, within one block of a car-share vehicle, or when the ADU is permitted with a new home (17.105.180(B)), and a garage, carport or space removed for an ADU need not be replaced (17.105.180(C)). The city's August 2020 ADU parking map shades most of the city north of US-50 as exempt (half a mile from the light rail stations and bus routes 10, 20 and 30) and none of the Folsom Plan Area south of it. The chapter does not list 66323 units among its exemptions, but HCD's March 2026 handbook says local agencies may not impose parking on 66323 units (Gov. Code 66323(b)), so the requirement should reach only local-standards detached units; the 2026 checklists print a flat one space per ADU without the per-bedroom alternative.

Every ADU and JADU needs a building permit (17.105.010(C)). The 66323 units (conversions, JADUs, the 800 sq ft new detached unit and multifamily units) are approved ministerially with no design review (17.105.090), and all other ADUs get a ministerial design review by the Community Development Director against the objective standards of 17.105.190 (and 17.105.200 in the Historic District) during plan check, for an added fee (17.105.110(A)). The city must rule on completeness within 15 business days and approve or deny within 60 days of a complete application, or the application is deemed approved, and a denial or incompleteness finding may be appealed to the Planning Commission for a final decision within 60 business days (17.105.050). A discretionary design review with public notice applies only when an applicant asks to deviate from the design standards (17.105.110(B)). Ord. 1361 ended Historic District Commission hearings for ADUs (the 3-24-2026 staff report: ADUs within the Historic District will no longer require a Commission hearing), and on 9-2-2026 staff told the Commission that an 850 sq ft ADU at 315 Sutter St. was subject only to ministerial review while the new house beside it went to the Commission; 17.52.300(D) still reads otherwise (see caveats).

Section 17.105.070(A) lets an ADU or JADU be rented separately from the home only for a term of 30 days or longer, and no one may occupy it until the city approves occupancy of the primary dwelling; 17.105.070(B) allows separate sale only to a qualified buyer under Gov. Code 66341, and the city has not opted into 66342 condominium conveyance. Gov. Code 66323(e) and 66333(g) require terms longer than 30 days for state-exempt units and JADUs, and the city already applies that wording: the 9-2-2026 conditions of approval for 315 Sutter St. say the rental must be for a term longer than thirty days, and the May 2026 ADU Design Workbook says all rental agreements must be more than 30 days and that Airbnb, VRBO and Vacasa use is not allowed. Folsom has no short-term rental ordinance or permit program; the Transient Occupancy Tax chapter taxes stays of 30 days or less in any hotel, a term that covers any structure rented to transients, but authorizes nothing (3.14.020, 3.14.030). The 30-day rule dates from the 2020 ordinance (Ord. 1306), and at the 3-4-2026 Historic District Commission hearing residents asked how the city would treat short-term rentals in ADUs built before 2020, a question staff said it would study.