ADU rules in Ames

Sec. 29.409(1)(a) permits an ADU 'on any lot' with only a single-family residence that is in a zoning district allowing a single-family residence as a principal use, and (2)(a)(ii) allows it 'detached from the single-family residence in a free-standing structure'. An existing detached accessory building (a garage, for example) may be converted, but only if it meets every current ADU standard including setbacks; a nonconforming outbuilding cannot be converted. A detached ADU is not treated as an accessory building under Sec. 29.408 and is exempt from the rear yard coverage limit there. Detached ADUs were first allowed by Ord. 4516 (1-9-2024).

Sec. 29.409(2)(a)(i) allows an ADU 'attached to the single-family residence', but (2)(a)(iv) says it 'May not be established within an existing single-family residence' and (3)(e)(i) requires attached ADUs to be 'of new construction and not a conversion of an existing dwelling'. So an addition built onto the house qualifies, while carving a basement or upper-floor apartment out of the existing house does not under the local text. An attached ADU with two doors facing the street must meet the two-family home design rules. Whether the bar on internal conversions survives Iowa Code 364.3(23), which defines an ADU as a unit 'either attached to or detached from' the house and voids conflicting local rules, is untested.

Sec. 29.409(4)(a) caps the ADU at '1,000 square feet or 50% of the size of the single-family residence, whichever is larger', with size meaning the house's gross living area excluding garages, decks and unheated porches, and unfinished basements excluded from the ADU's size (both added by Ord. 4596 to track SF 2369). Finishing an ADU basement later may be barred if it pushes the unit over the cap. Sec. 29.409(4)(b) limits the ADU to one bedroom. Height, setbacks, lot size, frontage, lot coverage, density and design follow the rules for the house on the lot; where side setbacks depend on height, a detached ADU gets its own setback based on its own height. Ord. 4596 also made ADU side and rear setbacks and lot coverage eligible for the 20 percent Alternative Design rule (Sec. 29.1502(7)). The original 2024 ordinance capped ADUs at 900 sq ft.

The current Sec. 29.409 contains no owner residency rule; the occupancy subsection (6) only points to Near Campus Neighborhood limits and rental registration. Iowa Code 364.3(23)(b)(4) bars any requirement 'requiring the property owner to be a resident'. The 2024 ordinance had required the owner to live in the house or the ADU, and the city's ADUs and Duplexes web page still says so; that page is stale.

Sec. 29.409(5)(a): 'No on-site parking is required for the ADU in addition to the required parking for the single-family residence.' The house's required parking must exist before an ADU is approved, and any parking provided must be paved and placed per Sec. 29.406. A paved on-site sidewalk must connect the ADU's main entrance to the parking area, the house or the street. The 2024 ordinance had required one space for the ADU.

Sec. 29.409(1)(a) states that 'An ADU is permitted on any lot' meeting the location test, so approval is by building permit and staff zoning review with no hearing, as Iowa Code 364.3(23)(c) requires ('without discretionary review or hearing'). On a lot in a local historic district or a locally designated property, the City or the Historic Preservation Commission may regulate an ADU it finds incongruous with the area and must record its reasons (Sec. 29.409(1)(c), the SF 2369 wording), and overlay zones such as O-SFC and O-H can add design standards.

Sec. 13.300(1) bars renting any dwelling unit unless 'it is registered as a rental dwelling with the Inspection Division' and holds a valid Letter of Compliance (fees and annual renewal apply), and Sec. 29.409(6)(b) repeats that a rented ADU must be registered. Occupancy is set per unit by bedroom count (Sec. 13.503(2)(e)(iii)); in the Near Campus Neighborhoods the bedroom count for occupancy is frozen at 1-1-2018 levels and cannot be raised by building an ADU (Sec. 13.503(2)(e)(iv)). Short-term rentals (30 days or less) require either full Chapter 13 compliance or a free voluntary Chapter 35 registration limited to the owner's primary residence (Home Share capped at 90 days a year). Iowa Code 414.1(1)(e) bars short-term-rental-specific regulation and fees except for safety, nuisance and similar purposes, so parts of Chapter 35 may be unenforceable.