ADU rules in Dubuque

Iowa Code 364.3(23) requires Dubuque to allow at least one accessory dwelling unit, attached or detached (including one in a detached garage), on a lot with a single-family residence, and voids conflicting local text. Dubuque's Unified Development Code has not been conformed: it still lists an accessory dwelling unit only as a conditional use (R-1, R-2, R-2A, R-3, R-4, OR, OC and C-1) and 16-3-7-3 still bars residential use of any accessory structure except through a conditional use permit. City planning staff told the Zoning Advisory Commission in September 2025 and February 2026 that the state code preempts the city code and that a single-family lot may now add an ADU by right once development standards are met and building permits are issued.

The state floor covers an ADU attached to the house (an addition, basement or internal conversion) as well as a detached one, so attached units are allowed wherever a single-family residence is an allowed principal use. The local conditional use text in 16-8-5-10 also contemplates attached units but still demands a conditional use permit, owner occupancy and a 600 sq ft cap; those conditions are void under 364.3(23)(d). The local text requires the principal dwelling to be a single-family detached dwelling, which matches the statute's single-family-residence trigger.

The codified Dubuque rule (16-8-5-10 E) caps an ADU at 50 percent of the principal dwelling's footprint or 600 gross sq ft, whichever is less; that cap conflicts with 364.3(23)(a)(2) and is void, so the operative cap is the larger of 1,000 sq ft or half the house. Since 7-1-2026 (SF 2369) the house's size means its gross living area excluding garages, decks and unheated porches, and unfinished basements do not count toward the ADU's size. A detached ADU otherwise follows the rules that apply to the house (for a single-family detached dwelling in R-1: 40 percent lot coverage, 30 ft height, 6 ft side and 20 ft rear setbacks), because 364.3(23)(b)(1) bars placement rules stricter than those for the house; the 15 ft accessory-structure height and 1,000 sq ft aggregate detached-structure limits in 16-3-7-2 cannot lawfully be applied more strictly to an ADU.

The codified Dubuque condition that "Either the principal dwelling or the accessory dwelling shall be owner-occupied" (16-8-5-10 B, as revised by Ord. 20-22 in 2022) is void: 364.3(23)(b)(4) bars any requirement that the property owner be a resident, and any familial, marital, employment, income or age restriction on occupants. City planning staff confirmed to the Zoning Advisory Commission on 9-3-2025 that the state code "has no owner occupancy or family requirement".

The codified ADU conditions still say the ADU "Shall provide one off street parking space" (16-8-5-10 H), but 364.3(23)(b)(3) bars additional parking beyond that required for the single-family residence and any fee in lieu, so that condition is void. The house itself remains subject to the general 16-14-6 table, which requires 2 spaces per single-family detached dwelling.

Under the codified text an ADU needs a conditional use permit from the Zoning Board of Adjustment after a noticed public meeting and findings under 16-8-5-4 (the Telegraph Herald reported a $600 fee in 2025). That discretionary step conflicts with 364.3(23)(c), which requires approval "without discretionary review or hearing" on the single-family timeline with written reasons for any denial, and is void. Staff describe the current path as by right with the required building permits, and the Zoning Board of Adjustment agendas and minutes from July 2025 to October 2026 carry no ADU conditional use cases. In the five historic preservation districts, exterior work still needs Historic Preservation Commission review or a staff no-material-effect determination before a permit issues (see caveats).

Dubuque requires a two-year rental license, issued by the City Manager with a council-set fee, for every dwelling unit let for rent (14-1J-3), and that general program applies to a rented ADU just as to any other rental. With the owner-occupancy condition void, both the house and the ADU may be rented. Short-term rentals (30 days or less) are a residential use that a city may not regulate through any ordinance or conditional use permit, nor charge a licence or permit fee for (414.1(1)(e)); the UDC's tourist home and bed and breakfast conditional uses cannot lawfully be applied to a short-term rental ADU beyond the safety, nuisance and emergency-contact purposes the statute preserves. Whether the general rental license reaches short stays is not addressed in the code text read.