ADU rules in Marion

Marion permits detached ADUs by right in every zoning district where one-unit dwellings are permitted: the use tables list 'Dwelling unit, auxiliary (detached)' as P in AG, RR-1, SR-E through SR-5, TR-1 through TR-4, U-1 and U-2. A detached ADU can be a separate structure or a unit built within or attached to an accessory structure such as a garage. Before Ordinance 25-32 (final consideration 12-2-2025) ADUs needed a conditional use permit in most residential districts; the city rewrote the rules to conform to Iowa's 2025 ADU law (SF 592), which also guarantees the right under Iowa Code 364.3(23)(a).

Attached ADUs (an internal unit entirely within the house or an attached addition) are permitted by right in the same districts as detached ones: AG, RR-1, SR-E through SR-5, TR-1 through TR-4, U-1 and U-2, every district that permits a one-unit dwelling. An attached unit must have its own living, sleeping, cooking and sanitation facilities and meet the egress rules of the building code (Chapter 126). A separate exterior entrance is optional.

§ 340-9.8(D) caps an ADU at 1,000 square feet or 50 percent of the principal one-unit dwelling, whichever is larger, matching Iowa Code 364.3(23)(a)(2); Ord. 25-32 removed the old 700 sq ft cap. The ADU follows the same setbacks, height limits, bulk and yard rules as a one-unit dwelling in the district, not the stricter accessory-building rules of § 340-9.2. At the 11-6-2025 hearing staff said the 50 percent is measured from the house's footprint; since 7-1-2026 SF 2369 defines the house's size as its gross living area excluding garages, decks and unheated porches and excludes unfinished basements from the ADU's size, so the statutory measure (usually larger than a footprint) governs. One ADU per lot with a single principal dwelling.

Marion's code no longer requires the owner to live on the property: Ord. 25-32 deleted the former rule that one unit be owner occupied (the council memo lists it as 'no longer enforceable'), and Iowa Code 364.3(23)(b)(4) bars any requirement that the owner be a resident. Instead, § 340-9.8(C) requires annual registration and inspection of any non-owner-occupied unit, whether the ADU, the house, or both. The ADU cannot be sold separately (§ 340-9.8(O)).

§ 340-9.8 sets no parking minimum for an ADU, and the residential parking schedule in § 340-8.2 has no ADU row (one space per dwelling unit applies to 'one-unit or two-unit dwellings', and the two-unit definition expressly excludes auxiliary dwelling units). Any parking or access serving the ADU must be on the same lot (§ 340-9.8(H)), a lot is limited to one driveway access point unless the City Engineer approves a second on a corner or double-wide lot (§ 340-9.8(G)), and a new garage built with an ADU must have its vehicle door set back 25 feet from the property line it faces (§ 340-9.8(I)). Iowa Code 364.3(23)(b)(3) bars additional parking or a fee in lieu.

ADUs are a permitted use (P in the use tables) and need only a building permit from the Community Development Department, then a certificate of occupancy after inspections, before anyone moves in (§ 340-9.8(P)). Ord. 25-32 ended the conditional use permit route the city had used since 2018. Iowa Code 364.3(23)(c) requires approval without discretionary review or hearing on the single-family timeline.

Either unit may be rented. Marion's Housing Code bars operating any rental dwelling unit without registering it and holding a landlord license (§ 126-91, IPMC 104.1 as amended), with regular inspections, and § 340-9.8(C) requires annual registration and inspection of any non-owner-occupied ADU or house. That is a general rental program, which Iowa Code 364.17 allows. Neither the zoning chapter nor the business licensing chapter has any short-term rental rule; Iowa Code 414.1(1)(e) bars cities from regulating short-term rentals (30 days or less) beyond safety, nuisance and similar rules enforced the same way as for other properties, and from charging a short-term-rental licence or permit fee. The city's rental housing page says short-term rentals (VRBO, Airbnb and the like) count as rental properties that must register. The ADU may not be sold, divided or owned separately from the house (§ 340-9.8(O)).