ADU rules in Sioux City

Iowa law requires Sioux City to allow at least one ADU, attached or detached, on the same lot as a single-family residence, and any conflicting city rule is void. Sioux City's code has not been updated to match. Section 25.02.260 still allows detached and two-story (above-garage) ADUs only in the AG, SR, UR, MU and NC.1 to NC.5 districts and bans them in General Residential (GR). It also requires a lot of at least 7,000 sq ft and limits ADUs to lots with a single-family detached house. Iowa Code 364.3(23)(b)(1) forbids lot-size, density and placement rules stricter than those for the house, and (23)(d) voids conflicting city rules, so the GR ban and the 7,000 sq ft minimum do not apply to an ADU next to a single-family residence. Since July 1, 2026, the state guarantee covers any zoning district where a single-family residence is an allowed principal use.

Section 25.02.260 allows 'integrated units' (an ADU inside or attached to the house, including basement units) in every listed district: AG, SR, GR, UR, MU and NC.1 to NC.5. The city's 7,000 sq ft lot minimum and its rule that ADUs may sit only beside a single-family detached house still appear in the code. Under Iowa Code 364.3(23)(b)(1) and (d), those rules are void where they are stricter than what applies to the house. The state definition in 364.3(23)(e) covers an ADU either attached to or detached from the single-family residence.

Iowa Code 364.3(23)(a)(2) sets the size floor: an ADU may be up to 1,000 sq ft or 50 percent of the single-family residence, whichever is larger. Since July 1, 2026 (SF 2369), the residence's size is its gross living area, excluding garages, decks and unheated porches, and unfinished basements are excluded from the ADU's size. Sioux City's unconformed § 25.02.260(9) still limits integrated units to 25 percent of the principal building's gross floor area and two-story or detached ADUs to 600 sq ft. Those caps conflict with the statute and are void under 364.3(23)(d). The city's 13 ft wall-plate and 24 ft ridge height limits for detached ADUs apply only to the extent the same limits apply to the house (364.3(23)(b)(1)).

Sioux City's ADU section (§ 25.02.260) and its procedure (§ 25.06.080.7) contain no owner-occupancy requirement. Iowa Code 364.3(23)(b)(4) separately bars any Iowa city from requiring the property owner to live on the property, from requiring a family, marital or employment relationship between occupants, and from restricting ADU occupancy by income or age. In the AG district, the table note letting the accessory unit be a farm-employee residence is an extra option, not a requirement for other ADUs.

Iowa Code 364.3(23)(b)(3) bars a city from requiring more parking for a lot with an ADU than for a single-family residence, or a fee in lieu. Sioux City's parking table (§ 25.05.030.2) requires 2 spaces per dwelling unit for a conventional home and adds a note that 'Additional parking is required if the lot includes an accessory dwelling unit'. That note, and the NC-district rule that integrated units show room for 'the required additional parking', are void under the statute. Converting a garage under § 25.02.260(4) still requires replacing the spaces lost. That survives only as far as the house's own 2-space requirement goes.

Sioux City approves an ADU through a zoning compliance certificate, which the Administrator issues or refuses within three working days and may issue alongside the building permit (§ 25.06.080.7). The administrative permits table (§ 25.06.060.2, amended by Ord. 2025-0605) still routes integrated and two-story ADUs through the Design Review Committee, whose recommendation goes to the Administrator. That table also lets the Administrator refer an application to the Planning and Zoning Commission. Iowa Code 364.3(23)(c) requires approval of a compliant ADU application 'without discretionary review or hearing' on the single-family timeline. Any discretionary design review, Commission referral, or case-by-case buffer requirement (§ 25.02.260(10)) is therefore void as applied to ADUs.

Under § 20.05.180, no landlord may rent any dwelling unit, or collect rent, without a valid rental permit. New rental properties get an initial inspection before the permit is issued. Under § 20.05.160 the annual fee is $40 for a single-family dwelling unit, plus a $50 new-registration fee. Title 25 has no short-term-rental provisions, and Iowa Code 414.1(1)(e) bars city regulation, licensing, or permit fees aimed at short-term rentals while classing them as a residential use. Iowa Code 364.3(23)(b)(2) bars ADU rental rules stricter than those general rental provisions. Separately, a bed and breakfast inn (a commercial use of the home) needs a conditional use permit to lodge guests in a guesthouse or accessory dwelling (Table 25.02.100, note 10).