ADU rules in Santa Rosa

Santa Rosa allows detached ADUs ministerially (an 'S' use, see specific use regulations) in the RR, R-1, R-2, R-3 and TV-R residential districts, in the OSR open-space district except the Southeast Greenway area and in OSC, and in the BP business park only when ancillary to a primary use; the use tables leave ADUs out of the MH (mobile home park), IL, IG and PI districts, and the commercial and mixed-use table (Table 2-6) has no ADU row at all, although § 20-42.130(B)(1) allows an ADU on 'any lot that allows a single-family or multifamily residential use and includes a proposed or existing dwelling'. A new detached unit needs 4-foot side and rear setbacks (8 feet on a street side, 5 feet for a unit built above a garage), a front setback like the house's (an 800 sq ft unit may go in the front setback when nothing else fits), and may be one story at 16 feet or two stories at 27 feet. The codified count in (E)(10)(a), restated by Ord. 2026-003, is two ADUs plus one JADU on a single-family lot (one new-construction attached or detached unit, one conversion unit and one JADU), while the city's ADU page lists up to three state-exempt Gov. Code 66323 units (a conversion ADU, a JADU and a new detached ADU of up to 800 sq ft) plus one Zoning Code (Gov. Code 66314) unit, which is the reading in HCD's March 2026 handbook. Multifamily lots may add up to eight detached ADUs on a lot with an existing building (never more than its unit count) or two with a proposed building, plus up to two new attached ADUs.

Attached ADUs (additions), ADUs converted from space inside a proposed or existing house or an accessory structure (a converted accessory structure may grow by 150 sq ft for a separate entrance), and junior ADUs of up to 500 sq ft inside a single-family home, including an attached garage, are all allowed ministerially under § 20-42.130. A new attached ADU is capped at 50 percent of the existing residential square footage but must be allowed at 850 sq ft (studio or one bedroom) or 1,000 sq ft (more than one bedroom) and may be 25 feet tall, while an ADU carved out of the house itself is capped at 45 percent of the house's habitable space and 1,200 sq ft with the same 850/1,000 sq ft floor. JADUs are allowed in every residential district including MH, one per parcel and only on a lot with a single detached single-family home, and a JADU needs its own bathroom unless it has an interior entry into the house. Multifamily buildings may convert non-livable space (storage rooms, boiler rooms, attics, basements, garages) into ADUs numbering up to 25 percent of the existing units, and at least one.

Section 20-42.130(E)(3) caps a newly constructed detached ADU at 1,200 sq ft of habitable space, a new attached ADU at 50 percent of the existing residential square footage (with 850 sq ft guaranteed for a studio or one-bedroom unit and 1,000 sq ft for more than one bedroom), and an ADU created entirely inside a single-family house at 45 percent of the house's habitable space excluding the garage and 1,200 sq ft, with the same 850/1,000 sq ft floor; a converted detached accessory structure keeps its existing dimensions plus 150 sq ft for an entrance, up to 1,200 sq ft. The caps are measured as 'habitable space', defined as conditioned space including closets, bathrooms, entries and hallways (§ 20-70.020), which the 3-10-2026 staff report says Ord. 2026-003 aligned with SB 543's interior-livable-space measurement in Gov. Code 66321(b); JADUs are capped at 500 sq ft. Heights are 16 feet for a one-story ADU, 18 feet with a roof pitch matching the house, 18 feet (20 with a matching pitch) within a half-mile walk of a major transit stop or high-quality transit corridor, 18 feet beside a multistory multifamily building, 25 feet for an attached ADU, and 27 feet for any two-story ADU or ADU over a garage. Lot coverage limits apply but may never block an 800 sq ft one-story unit with 4-foot side and rear setbacks (E.1, E.5), and the state-exempt Gov. Code 66323 units (the 800 sq ft detached unit and conversions of existing space) sit outside the local caps, the 45 percent conversion limit included.

Santa Rosa imposes no owner-occupancy requirement on ADUs: § 20-42.130 contains none, the city's ADU page and FAQ say owner occupancy is 'Not required' for ADUs, and Gov. Code 66315 bars owner-occupant requirements for ADUs. Subsection (E)(17) still reads 'The Department shall not impose an owner-occupant requirement on an accessory dwelling unit before January 1, 2025', a leftover from the 2020 to 2024 statutory moratorium that no longer describes a live rule, since nothing in the code imposes one after that date and 66315 now forbids it. For JADUs, Ord. 2026-003 implemented AB 1154: the recorded deed restriction making the JADU legal only while the owner lives in the house or the JADU applies only when the JADU shares sanitation facilities with the house ((F)(4)(d), (G)), matching Gov. Code 66333(b), and it never applies when the owner is a governmental agency, land trust or nonprofit housing organization.

Section 20-42.130(E)(11) requires one off-street space per ADU, which may be uncovered, compact, tandem or in a setback, but waives it when the ADU is 750 sq ft or less or a studio, within one-half mile walking distance of public transit, in a historic preservation district, part of the existing primary residence or an existing accessory structure, where on-street parking permits are required but not offered, within one block of a car-share vehicle, or applied for together with a new single-family or multifamily dwelling; the applicant supplies the evidence (a transit map, for example). JADUs need no parking ((F)(4)(f)), and no replacement parking is required when a garage, carport, covered structure or uncovered space is converted or demolished for an ADU ((E)(11)(i)). Gov. Code 66323(b) bars parking requirements on the state-exempt units (the 800 sq ft detached unit and conversions), and 66322(a)(3) exempts a unit that is part of a proposed or existing residence or an accessory structure, wording broader than the local 'existing' text; the state exemptions govern, which is why the city's ADU page says only that a space 'may be required for some new detached ADUs'. The parking table (Table 3-4, § 20-36.040, as amended by Ord. 2026-003) repeats the one space 'unless exempted by Section 20-42.130.E.9', a stale cross-reference to what is now (E)(11).

An ADU or JADU application that complies with § 20-42.130 'shall be approved ministerially' ((C)): the ADU permit is filed together with the building permit and decided by the Planning and Economic Development Director (Table 5-1), completeness is determined within 15 business days or the application is deemed complete, and a complete application is approved or denied within 60 calendar days or deemed approved, with no hearing. Since Ord. 2026-003 (implementing SB 543), an incompleteness finding or a denial can be appealed in writing to the Planning Commission, which must issue a final written determination within 60 business days ((D)(2)(f); Table 6-1). A permit cannot be denied over nonconforming zoning conditions or unpermitted structures that pose no health and safety threat, or for an unpermitted ADU built before 1-1-2020 unless correction is needed for health and safety ((C)(2)-(3)). ADUs that comply with the section need no Landmark Alteration Permit in a preservation district (§ 20-58.060) and instead meet the objective compatibility test in (E)(14) (matching color, siding and architectural features, or a qualified historic resource survey); only an accessory structure attached to an ADU and larger than half its floor area falls back on whatever discretionary review the Zoning Code requires ((E)(12)(b)).

Section 20-42.130(B)(4) and (F)(1)(c) bar ADU and JADU rentals 'with terms of less than 30 days', which matches Gov. Code 66315's allowance of a 30-days-or-longer minimum for ordinary ADUs; for state-exempt Gov. Code 66323 units and for JADUs, state law requires terms longer than 30 days (66323(e), 66333(g)), and the JADU article supersedes conflicting local text (66339.5). Chapter 20-48 (rentals under 30 consecutive days) bars short-term rental permits for ADUs and JADUs, except that an ADU whose STR permit was issued and in effect may keep operating until the permit lapses, is revoked or is not renewed, after which it cannot be reissued (§ 20-48.040(A)(4)(b), added by Ord. 2023-011 of 7-25-2023); an owner who lives on the parcel may host a short-term rental only in the primary residence, and non-hosted permits are frozen under a shrinking citywide cap of 182 with no new applications accepted. ADUs may not be sold or conveyed separately from the primary residence ((B)(5); (G)(1) for JADUs), Santa Rosa has not opted into Gov. Code 66342 ADU condominiums, and the 66341 qualified-nonprofit sale path applies under state law although the code does not mention it. The city's only local rent control, Chapter 6-66, covers mobilehome spaces, so it does not reach ADUs.