ADU rules in Iowa City

Iowa City allows one ADU, detached or attached, on the same lot as a single-family residence; the zoning definition (14-9A-1) covers a unit 'either attached to or detached from the single family residence', tracking Iowa Code 364.3(23). Ordinance 26-4989 (passed 6-16-2026) adds the SF 2369 wording that the ADU is allowed 'within a zoning district where a single family residence is an allowed principal use', and repeals the old form-based 'carriage house' building type (32 by 24 foot footprint, 2 stories, 15 feet from the house) so detached ADUs in the T3 and T4 zones follow 14-4C-2A instead. A detached ADU is not held to the accessory building rules of 14-4C-3 unless those are more permissive than the principal building standards of 14-2A-4.

Attached and internal ADUs (basement, addition, conversion) are allowed on the same terms as detached ones under 14-4C-2A, which permits one ADU per lot with a single-family residence. The unit must be a complete, independent dwelling with its own kitchen, bathroom and exterior entrance. The older rule that an ADU inside an existing building must look like the principal use and match its materials was removed in the 2026 conformance and is barred anyway by Iowa Code 364.3(23)(b)(1).

14-4C-2A(5) caps the ADU at 'fifty percent (50%) of the total floor area of the principal use or one thousand (1,000) square feet, whichever is larger', matching the state floor in Iowa Code 364.3(23)(a)(2). Ordinance 26-4989 adds that floor area 'is measured to the outside surface of exterior walls and excludes unfinished basements', following SF 2369. Height, setbacks and coverage for a detached ADU follow the principal building standards of the base zone; the city cannot impose stricter placement rules than for the house. Before 2026 the code used 'whichever is less' and required the owner to live on site.

The codified ADU standard no longer contains an owner occupancy rule: the pre-2026 text ('The owner of the property on which an ADU is located must occupy at least one of the dwelling units on the premises as the permanent legal resident') was deleted by the 2026 conformance, and Iowa Code 364.3(23)(b)(4) bars any requirement 'requiring the property owner to be a resident'. The code does still require that 'The ADU and the principal use must be under the same ownership', so the ADU cannot be sold separately. The housing code definition in 17-5-3 still describes an ADU as accessory to an 'owner-occupied' use; that leftover wording is void under 364.3(23)(d).

The minimum parking table in 14-5A-4 carries no ADU-specific line, and the city removed its separate ADU parking space requirement in its 2023 housing amendments. Iowa Code 364.3(23)(b)(3) independently bars 'additional parking beyond that required for a single family residence or payment of a fee in lieu'.

14-4C-2A states that 'ADUs are permitted provided the following conditions are met', so an ADU needs only the building permit and staff zoning review, with no board of adjustment hearing. Iowa Code 364.3(23)(c) requires approval 'without discretionary review or hearing' on the single-family review timeline. Properties in a local historic or conservation district also need historic review of exterior work.

Iowa City requires a certificate of structure compliance and a rental permit to let any dwelling unit (17-5-16A), so a rented ADU goes through the city's rental inspection program like any other rental. Short-term rentals, defined as property 'offered for a fee of thirty (30) days or less', may operate only with a valid rental permit, but 'no application or inspection fee may be charged' (17-5-16E), consistent with the state ban on short-term rental license fees in Iowa Code 414.1(1)(e)(4). The ADU must stay under the same ownership as the house (14-4C-2A(2)).