ADU rules in Fairfield

Detached ADUs are allowed on any lot where a single-family dwelling, duplex, duet or multifamily dwelling is a permitted use and one exists or is proposed (FMC § 25.20.4.11(D)(1)(a)); Table 25-1 sends 'Accessory dwelling units and junior accessory dwelling units' in all six residential districts (RVL, RL, RLM, RM, RH, RVH) to that section, and the commercial table (Table 25-9) and the Heart of Fairfield table (§ 25.23.2) do the same wherever housing is allowed. A detached unit outside the state-exempt path must sit 4 ft from side and rear lot lines, meet the zone's front setback and stand 5 ft from the main house, and it must echo the main home's materials and form when visible from the street, use clerestory windows within 15 ft of a neighboring side yard and rest on a permanent foundation ((D)(2)-(3)). The codified count from Ord. 2023-04 is 'one detached ADU and one JADU, or one ADU' per single-family, duplex or duet lot, but Gov. Code 66323(a) requires ministerial approval of any combination of a conversion ADU, a detached new-construction ADU of up to 800 sq ft with 4-ft setbacks and a JADU, and state law controls where they differ (66325). On lots with an existing multifamily building, (D)(1)(b) defers to the state counts, now up to eight detached ADUs but never more than the number of existing units, or two with a proposed multifamily building (66323(a)(4)).

ADUs attached to the home as additions, or created inside the existing or proposed home, an attached garage or an existing accessory structure, are allowed on the same lots as detached units (§ 25.50.2 defines an ADU as 'an attached or detached residential dwelling unit'). Conversions of existing living area or an accessory structure need no setbacks ((D)(2)(b)(i)), and a garage may be converted to an ADU or JADU without replacing the lost parking (§ 25.20.4.3(B)). Units carved from existing space that meet the state-exempt test (cited in the code as Gov. Code 65852.2(e)(1), now 66323(a)(1), which allows up to 150 sq ft of expansion for ingress and egress) skip the Planning ADU Permit and the local development standards ((B)(3), (D)(2)). One JADU of 220 to 500 sq ft is allowed per lot where single-family use is permitted, entirely within a single-family home or duet, with an efficiency kitchen and either its own bathroom or shared sanitation with an interior connection to the main home ((E); § 25.50.2). On existing multifamily buildings, conversions of non-livable space such as storage rooms, attics, basements and garages are allowed up to 25 percent of the existing units, at least one (66323(a)(3)).

§ 25.20.4.11(D)(2)(a) caps an attached ADU at '50 percent of the floor area of the primary dwelling or 1,200 square feet, whichever is less' and a detached ADU at 1,200 sq ft, and (D)(2)(c) waives lot coverage, floor area ratio, setback or other standards that would block an 800 sq ft, 16-ft ADU with 4-ft side and rear setbacks; JADUs run 220 to 500 sq ft ((E)(2)(b)). State law sets floors the percentage cap cannot undercut: no maximum below 850 sq ft of interior livable space, or 1,000 sq ft for more than one bedroom, and no percentage, coverage or floor-area limit that blocks an 800 sq ft unit (Gov. Code 66321(b)(2)-(3)), while state-exempt conversions are limited only to existing space plus 150 sq ft and a state-exempt detached unit may be held to 800 sq ft (66323(a)(1)-(2)). Height is 16 ft to the roof peak for every ADU, or 25 ft for the whole structure when more than half of the ADU's gross floor area sits above a garage ((D)(2)(a)(iii)); state floors raise an attached ADU to 25 ft or the main-house limit if lower (35 to 50 ft in the standard residential tables, but 18 ft for main dwellings under the SB 9 Table 25-2.1) and a detached ADU to 18 ft within one-half mile walking distance of a major transit stop or high-quality transit corridor (plus 2 ft for a matching roof pitch) or on a lot with a multistory multifamily building (66321(b)(4)). The section does not say how ADU size is measured; the code's gross floor area runs to the exterior faces of walls (§ 25.50.2) while the state floors are stated in interior livable space. If the ordinance is void under Gov. Code 66316 or 66326(d) (see caveats), the state default applies instead: attached ADUs up to 50 percent of the existing home with no 1,200 sq ft ceiling and detached ADUs up to 1,200 sq ft (66314(d)(4)-(5)).

Fairfield imposes no owner-occupancy requirement on ADUs, at application or afterward, and Gov. Code 66315 forbids one. For JADUs, § 25.20.4.11(G) still says owner occupancy 'is required for any property with a JADU' (the owner may live in the main home or the JADU; government agencies, land trusts and housing organizations are exempt), and (H) requires a recorded JADU deed restriction before the certificate of occupancy. Since 1-1-2026, Gov. Code 66333(b) as amended by AB 1154 and SB 543 allows a JADU owner-occupancy requirement only where the JADU shares sanitation facilities with the main home, so a JADU with its own bathroom carries none and the universal local clause yields (66325). The JADU deed restriction itself is lawful because 66333(c) requires one barring separate sale and fixing the unit's size and attributes; HCD's 10-8-2025 letter to the city restated that deed restrictions on ADUs are barred, and Fairfield's code imposes none on ADUs.

§ 25.20.4.11(C)(4) provides that 'No additional parking shall be required to be provided for either an ADU or a JADU', and the parking table in § 25.34.4 repeats it on the 'Accessory dwelling units' row ('No additional parking shall be required. See § 25.20.4.11.'). Garages may be converted to an ADU or JADU without replacing the displaced spaces (§ 25.20.4.3(B), added by Ord. 2023-04), matching Gov. Code 66314(d)(11). This is more generous than state law, which would let a city require up to one space per ADU or per bedroom outside the 66322(a) exemptions (66314(d)(10)) and bars parking for JADUs (66334(a)); 66325(b) preserves less restrictive local rules, so the answer is the same whether the codified text or state law alone governs. The only related standard is the driveway rule: no more than 40 percent of a lot's frontage may be driveway, with flexibility for cul-de-sac, flag and narrow corner lots ((D)(3)(f)).

Outside the state-exempt path an ADU needs a Planning ADU Permit that § 25.20.4.11(B)(2)(b) says 'shall be processed and considered ministerially, without discretionary review or a public hearing ... within 60 days of submittal of a complete application', followed by a building permit; units meeting the state-exempt criteria (cited as Gov. Code 65852.2(e)(1), now 66323) and every JADU skip the planning permit and file a building permit directly with the Building Division ((B)(3)). Planning applications are filed through the city's Fairfield BUILD online portal, and Gov. Code 66317 adds a 15-business-day completeness determination and deemed approval if the city has not acted within 60 days of a complete application. Table 25-1 routes ADUs in every residential district to § 25.20.4.11 rather than to a P or C cell, so no use permit applies. Administrative add-ons: windows within 15 ft of a neighboring side yard must be clerestory unless the neighbor consents or the Zoning Administrator approves an over-the-counter Plan Review ((D)(3)(c); § 25.40.3), and properties on a historic register must show substantial compliance with the Secretary of the Interior's guidelines ((B)(6)). Hillside (H) overlay findings (§ 25.28.4(E)) yield to 66317 for ADUs, while lots in the Suisun Marsh management areas face a Marsh Development Authorization hearing (§ 25.40.7) noted in the caveats.

§ 25.20.4.11(C)(2): 'An ADU or JADU may only be rented, leased, and/or occupied for residential purposes. If an ADU or JADU is rented, it shall not be rented for a period of less than 30 consecutive days.' Gov. Code 66315 lets a city require rental terms of 30 days or longer for ordinary ADUs, while state law requires terms longer than 30 days for units approved on the state-exempt path (66323(e)) and for JADUs (66333(g)). Fairfield has no short-term rental permit program: eCode360 searches on 2026-10-06 for 'short-term rental(s)', 'vacation rental', 'home sharing' and 'Airbnb' found nothing in the code, the New Laws bank or public documents, and Table 25-1 lists no transient lodging use in the residential districts (bed and breakfast inns are defined as transient lodging but not listed, and unlisted uses are not allowed under § 25.20.2(B)), so the bar would hold even if the 30-day clause fell with the ordinance. (C)(1) adds 'No ADU or JADU shall be sold separately from the primary residence'; the city has not opted into Gov. Code 66342 condominium conveyance, leaving only the state 66341 qualified-nonprofit route. No city rental registration, rental inspection or rent-stabilization ordinance appears in the code (searched 2026-10-06).