ADU rules in Rialto

RMC § 18.10.070(C), added by Ord. No. 1641 (7-14-2020) and never amended, makes ADUs a permitted use on every lot in Rialto's single-family and multifamily residential zones, attached or detached, and § 18.10.020(J) lists them as a permitted R-1 use. The local text caps a single-family lot at one ADU plus one JADU and a multifamily lot at two detached ADUs (§ 18.10.070(J)), but Gov. Code § 66323(a) overrides both counts: a single-family lot can combine a conversion ADU, a JADU and one detached new-construction ADU (the state-exempt unit, up to 800 sq ft with 4 ft side and rear setbacks), and a lot with an existing multifamily building can add up to eight detached ADUs, never more than its existing unit count. Detached units must sit at the rear or side of the main home unless the Community Development Director finds lot constraints (§ 18.10.070(E)), must match its architecture (G), and are held locally to 16 ft or one story (T), which state law raises to 18 ft near a major transit stop or high-quality transit corridor and on lots with a multistory multifamily dwelling (§ 66321(b)(4)(B)-(C)). From 1-1-2027 AB 956 (Ch. 791, Stats. 2026) allows two detached new-construction ADUs on a single-family lot under § 66323.

§ 18.10.070(C) allows ADUs attached to or within a proposed or existing primary dwelling, including attached garages and storage areas, and § 18.10.070(K) allows conversion of any legally permitted attached or detached structure with no new setback and up to 150 sq ft of expansion for access. Attached units need a separate outside entrance that is not on the front elevation of the main home (Q), and JADUs of up to 500 sq ft must sit entirely within a single-family residence (B.1.c). The local 16 ft or one-story limit (T) conflicts with Gov. Code § 66321(b)(4)(D), which guarantees attached ADUs 25 ft or the main home's zone height, whichever is lower, up to two stories; Rialto planning staff told the Economic Development Committee in 2025 that state law allows two-story ADUs where the main home is two stories. In multifamily buildings the local one-per-four-units conversion rule (J) yields to § 66323(a)(3): at least one conversion ADU and up to 25 percent of the existing units.

§ 18.10.070(P) caps every ADU, attached or detached, at 850 sq ft, or 1,000 sq ft with more than one bedroom, or 50 percent of the primary dwelling where that is larger, and in no case over 1,200 sq ft: a 1,600 sq ft home gets 850 or 1,000 sq ft, a 2,200 sq ft home 1,100 sq ft, and a home of 2,400 sq ft or more 1,200 sq ft. Lot coverage and floor-area limits cannot block an 800 sq ft unit (S), the state-exempt detached unit is 800 sq ft (Gov. Code § 66323(a)(2)), conversions may add 150 sq ft for ingress and egress (K, P), and JADUs are capped at 500 sq ft (B.1.c). The formula respects the state floors in § 66321(b)(2), but the code states plain square footage where the state floors count interior livable space, and the whole 2020 ordinance is exposed to Gov. Code § 66316: Rialto's planning staff reported in 2025 that state law changes left it out of compliance, and if it is treated as void the state standards apply instead (detached 1,200 sq ft flat under § 66314(d)(5); attached 50 percent of the existing home under § 66314(d)(4), with the § 66321(b)(3) 800 sq ft guarantee). Height is 16 ft or one story locally (T), against state floors of 18 ft near major transit or on multistory multifamily lots and 25 ft for attached units.

§ 18.10.070(H) says owner occupancy 'shall not be required of either the primary unit or the accessory dwelling unit', matching Gov. Code § 66315, which bars owner-occupancy conditions on ADUs. The same subsection still requires the owner to live in the main home or the JADU for every junior unit, but since 1-1-2026 Gov. Code § 66333(b) (AB 1154) allows that requirement only where the JADU shares sanitation facilities with the house, and never when the JADU has its own bathroom or the owner is a public agency, land trust or housing organization; state law controls the conflict (§ 66325(a)). The fall 2025 committee draft would have kept a universal JADU owner-occupancy rule, but it was never adopted. The three-year owner-occupancy affidavit for an SB 9 urban lot split (§ 17.51.050(M)(3)) is a lot-split rule, not an ADU rule.

§ 18.10.070(N) requires one off-street space per ADU or per bedroom, whichever is less, on top of the main home's parking; it may be tandem on an existing driveway (at least 9 by 20 ft and outside the public right-of-way) or in setback areas, and garage, carport or covered spaces lost to an ADU need not be replaced. No space is required within one-half mile walking distance of public transit, in an architecturally and historically significant historic district, for a unit within the existing home or an existing accessory structure, where on-street permits are required but not offered, or within one block of a car-share vehicle. State law widens these exemptions whatever the local text says: § 66322(a)(3) covers units within a proposed as well as an existing home or any accessory structure, § 66334(a) bars parking for JADUs (which Rialto's code counts as ADUs), § 66323(b) bars local standards such as parking on state-exempt units, and § 66314(d)(11) extends the no-replacement rule to uncovered spaces. In practice a new local-standards unit away from transit needs one space, and the city checklist asks for a vicinity map to prove transit proximity.

Under § 18.10.070(D) an ADU needs a development application to the Community Development Department and must be 'ministerially approved or denied within sixty days, without a hearing' once complete, consistent with Gov. Code § 66317 (15-business-day completeness check, 60-day decision, no discretionary review). In practice the Planning Division issues an address letter after an informal review and Building and Safety issues the building permit through the Online Permit Center, with plan check scheduled within 30 business days (city ADU page). The city also lists pre-selected plans from Menifee and Chino (306 to 1,000 sq ft) licensed through their designer for $5,000 to $7,000. No zone requires a hearing for an ADU; building-code disputes go to the Building Appeals Board, which on 12-17-2025 upheld a refusal to legalize a JADU under Gov. Code § 66311.7 (then numbered § 66332) because the owner could not show it predated 1-1-2020.

§ 18.10.070(H) lets an ADU be occupied without limits but, 'if rented, such rental shall be for a period greater than thirty days', so stays of 30 days or less are barred for every ADU and JADU; that is one day stricter than Gov. Code § 66315 allows for an ordinary ADU on a single-family lot (terms of 30 days or longer) and matches the longer-than-30-day terms state law itself requires for state-exempt units (§ 66323(e)) and JADUs (§ 66333(g)). § 18.10.070(I) bars selling the ADU separately and any subdivision, condominium or cooperative split, so Rialto has not opted into Gov. Code § 66342 ADU condominiums and only the qualified-nonprofit sale route of § 66341 remains. Rialto has no short-term rental permit program; the nine percent transient occupancy tax (Chapter 3.08) reaches stays of 30 days or less, but its registration certificate 'does not constitute a permit', and lots built under SB 9 also bar rentals under 30 days (§§ 17.51.050(M)(2), 18.113.050(I)(2)). A parcel with three or more rented units (for example a house, an ADU and a JADU all rented) falls under the Chapter 15.58 multi-family rental fire inspection program, and Chapter 5.70 charges an annual business license fee for renting three or more units.