ADU rules in Dickinson County

Detached ADUs are allowed on any unincorporated lot with a single-family house, including a unit inside a detached garage or other accessory building. The Board of Supervisors added Letter F to Article 17, Section 7 of Zoning Ordinance 102 on September 16, 2025, changing the old flat ban ("No accessory building shall be used for dwelling purposes") to allow dwelling use when the ADU standards are met. Iowa Code 331.301(29) independently requires every county to allow at least one ADU, attached or detached, beside a single-family residence. Single-family homes are permitted principal uses in the A-1, R-1, R-2, R-3, R-4 Lakeshore and RE Resort Enterprise districts, which together cover the farm ground and the unincorporated lakeshore around Spirit Lake and East and West Okoboji.

Attached and internal ADUs (a basement apartment, an addition or a conversion inside the house) are allowed under Iowa Code 331.301(29), which defines an ADU as attached to or detached from the single-family residence. The county's September 2025 amendment sits in the accessory buildings section and does not address attached units, but the statute governs and voids conflicting local text, including Article 4, Section 6(C)'s one-principal-structure-per-lot rule to the extent it would be read against an ADU. The same size, permit and occupancy rules apply to both forms.

The county's Letter F.2 restates the state floor: an ADU "shall not exceed one thousand square feet or fifty percent of the size of the single-family residence whichever is larger", so a 2,400 sq ft house supports a 1,200 sq ft ADU and any smaller house still gets 1,000 sq ft. Since July 1, 2026 (SF 2369) unfinished basements are left out of the ADU's size and the house's size is its gross living area excluding garages, decks and unheated porches; the county text has not been updated for that. Letter F.6 puts ADUs on the district's principal-building setbacks (for example R-4 Lakeshore: 30 ft front from the lake side, 5 ft side, 25 ft rear; R-1: 50 ft front, 15 ft side, 25 ft rear). The 22 ft accessory-building height cap in Article 17, Section 7(C) is stricter than the 35 ft house height in every residential district, so under 331.301(29)(b)(1) it cannot limit an ADU below the house's height limit.

No owner-occupancy requirement. The county's Letter F lists six ADU standards and none of them requires the owner to live on the property, and Iowa Code 331.301(29)(b)(4) bars a county from requiring the property owner to be a resident or requiring any family, marriage or employment relationship between the occupants of the house and the ADU. The only owner-occupied use in the ordinance is the separate Bed and Breakfast use type, which is not an ADU.

The ADU itself needs no added parking. Article 18, Section 3(A) of the zoning ordinance still reads "Single Family, Duplex, and Two Family Residential: Two (2) spaces per dwelling unit", which read literally would demand two more spaces for the ADU, but Iowa Code 331.301(29)(b)(3) bars a county from requiring parking beyond that required for the single-family residence or a fee in lieu, so only the house's two spaces apply. The county's 2025 ADU amendment says nothing about parking.

An ADU needs a zoning compliance permit from the Zoning Administrative Officer (Letter F.5: "A accessory dwelling unit permit is required and subject to the standards above"); staff told the commission in May 2025 that it falls under the ordinary Zoning Compliance Application rather than a separate form. Article 25, Section 3 requires compliance permits to be "issued to complying applicants within seven (7) days after application is made", and the fee follows the same value-based zoning compliance schedule as a house (Resolution 2025-27, September 16, 2025, from $50 up to $825). No hearing is involved, consistent with 331.301(29)(c), which requires approval without discretionary review on the single-family timeline. Sewage and water must meet the county sanitarian's rules (Article 4, Section 6(E)), which matters on septic lots away from the lake sewer districts.

The ADU or the house may be rented long term; the county runs no rental registration or licensing program and its ADU amendment imposes no rental rule, and 331.301(29)(b)(2) bars rental rules stricter than 331.301(18) and chapter 562A. For stays of 30 days or less, 331.301(18) forbids a county to adopt or enforce any regulation or conditional use requirement relating to short-term rental properties, classifies them as residential land use, and forbids a short-term rental license or permit fee. The zoning ordinance still treats a house "rented to the general public for periods not exceeding one calendar month" as a "Commercial Single Family" use listed only in R-4 Lakeshore, and the West Okoboji Harbor overlay (Article 34, Section 3) says rentals "may not be less than for one month increments"; both conflict with 331.301(18) and are unenforceable as rental limits, though general noise, nuisance, parking and safety rules apply equally. Homeowners association bylaws, such as the West Okoboji Harbor lot owners' association, can still limit rentals privately.