City staff outline ADU code changes to comply with state bill, propose loosening owner‑occupancy and size limits

Des Moines planning staff briefed the council April 3 on proposed amendments to the city’s accessory dwelling unit (ADU) regulations to comply with recent state legislation identified in staff materials as “HB 13 37.” The city plans to bring code amendments (staff cited municipal code sections in packet materials) forward for public hearing and adoption to meet the state compliance deadline.

Staff described the main proposed changes: • Impact fees: the draft limits ADU impact fees to 50% of the principal unit fee, consistent with staff’s reading of the state requirement. • Owner‑occupancy: the city’s current code requires owner‑occupancy of one unit on the lot; the proposed amendment would remove that requirement to comply with state law. • Number and configuration: where Des Moines currently permits one ADU per residential lot, staff propose permitting at least two ADUs per lot in any configuration to meet statutory minimums; staff noted the city’s broader “middle housing” work could affect the final unit counts and that allowing more ADUs could affect the city’s ability to collect certain infrastructure fees tied to other regulatory frameworks. • Size: staff proposed retaining the city’s existing 350 square‑foot minimum but increasing the maximum size for ADUs to 1,000 square feet in order to conform with the state standard in the bill. • Location and setbacks: staff would retain underlying zone setbacks but add the state requirement allowing ADUs to be sited at a lot line abutting a public alley in most cases. • Conversions and sales: the proposed code would clarify that legal nonconforming ADUs can be converted and that ADUs may be sold as condominiums as required by the legislation. • Parking: the draft keeps the city’s one‑stall requirement for off‑street parking for ADUs but would add the state language that precludes requiring off‑street parking where the ADU is within a half‑mile walking distance of a major transit stop.

Staff said they propose keeping the existing 350 square‑foot minimum to avoid converting very small structures that historically did not require permits. On the number of units, staff described the tension between allowing more units as ADUs and the implications for impact fees and street improvements; some jurisdictions the staff cited are proposing a simplified approach of allowing four units per lot in some areas to avoid different rules across ADU and “middle housing” codes. Staff asked the council for direction and noted that the formal draft ordinance will return at a public hearing timeline before the state deadline (staff cited June but also discussed the June 30 deadline in conversation).

Council discussion touched on parking impacts, flexibility for larger lots, interaction with forthcoming middle‑housing rules and potential incentives or limits tied to affordability and transit proximity. Several council members asked staff to include flexibility for situations with larger lots or garage conversions and to consider ways to minimize additional on‑site parking burdens where feasible. Staff said the law limits some local discretion (such as owner‑occupancy and impact‑fee maximums) but that council direction could shape the number of units allowed and the choice of whether some units are regulated under middle housing or ADU provisions.

Ending: Staff will return with a draft ordinance for public hearing and council consideration and requested direction on the council’s preferences for unit counts, parking flexibility and any lot‑size approaches for additional ADUs.