ADU rules in Des Moines

Detached ADUs are permitted by right in the A, DXR, RX1, RX2, N and NX districts where accessory to a one-household dwelling, as a stand-alone ADU building or inside a detached outbuilding such as a garage. A detached ADU building must sit in the rear yard and be set back at least five feet from every lot line, with height capped at the maximum allowed for the principal building and roof types limited to those allowed for principal buildings. Ordinance 16,510 (adopted 10-20-2025, effective 11-7-2025) rewrote the section to align with the 2025 state act, which requires every Iowa city to allow one ADU on a single-family lot.

An ADU may be located internally within the principal dwelling, which covers basement and other interior conversions and attached additions, in the same A, DXR, RX1, RX2, N and NX districts where accessory to a one-household dwelling. The city's ADU page describes attached, garage and internal (including basement) ADUs as allowed types. Iowa Code §364.3(23) independently guarantees an attached or detached ADU on any single-family lot.

Section 134-3.9.2(D), as rewritten by Ordinance 16,510, mirrors the state floor exactly: an ADU may not exceed 50 percent of the floor area of the principal household unit or 1,000 square feet, whichever is larger. One ADU per lot. A detached ADU building is limited to the maximum height permitted for the principal building, must be in the rear yard, and must be set back five feet from all lot lines; in N and NX districts all accessory structures together are also held to 576 sq ft or 25 percent of the rear yard, whichever is greater, a coverage cap that state law lets apply only to the extent it applies to the house. Since 7-1-2026 the state measures the house by gross living area excluding garages, decks and unheated porches and excludes unfinished basements from the ADU's size (SF 2369); the local text has not been updated for that.

The current ADU section (§134-3.9.2, as amended by Ordinance 16,510 effective 11-7-2025) contains no owner-occupancy requirement, and the city's ADU page says the ADU and the primary house can be rented to separate tenants. Iowa Code §364.3(23)(b)(4) bars any requirement that the property owner be a resident. The separate boarding and rooming accessory use (§134-3.9.8(A)) still requires an owner to reside on the property, but that rule covers renting rooms to boarders, not ADUs.

The city's ADU page states: 'City Code requires a minimum of 1 off-street parking space for the primary house. Additional parking for the ADU is not required.' Section 134-3.9.2 sets no ADU parking standard. Table 135-6.4-1 still lists household living at 1 space per household unit, but Iowa Code §364.3(23)(b)(3) bars any parking beyond that required for the single-family residence, or a fee in lieu, so no space can be demanded for the ADU. DX districts have no parking minimums at all.

ADUs that comply with §134-3.9.2 are 'permitted' in the listed districts, so approval is through a building permit from the Permit and Development Center with staff zoning review; no conditional use or board hearing applies. Iowa Code §364.3(23)(c) requires approval without discretionary review or hearing and on the single-family review timeline. Exterior work in a local historic district (for example Sherman Hill) can additionally need a Historic Preservation Commission certificate of appropriateness.

Chapter 60 requires a rental business license, with inspections, before any dwelling unit is rented; the exemption covers only units occupied by the owner or the owner's nuclear family, and the city's ADU page applies that same standard to ADUs and says both units can be rented to separate tenants. Short-term rental (lodging for less than 30 consecutive days) of a household unit or part of one is allowed as an accessory use to a household living use under §134-3.9.8(B); Iowa Code §414.1(1)(e) bars STR-specific regulation, conditional use requirements and STR license or permit fees. Household living tenancy is otherwise defined as month-to-month or longer. ADUs are assigned their own address and taxed as residential property; no code section addresses separate sale, which would require a lot split under normal subdivision rules.