ADU rules in West Des Moines

West Des Moines calls ADUs "second dwelling units" (SDUs). Table 5.1 of section 9-5-8 lists "Second dwelling" as a permitted (P) use in the RE, RS, R-1, SF-CR, SF-VJ, MH and OS districts, exactly the districts where a detached single-family dwelling is permitted, and 9-5-4(F)(3) says an SDU "may be detached from or attached to the single family dwelling"; the 9-2-2 definition includes a unit incorporated into a detached garage. The city conformed this text to Iowa Code 364.3(23) by Ord. 2662 (adopted 7-7-2025). RM and RH, where single-family dwellings are not a permitted use, allow no SDU, which matches the SF 2369 wording (an ADU must be allowed where a single-family residence is an allowed principal use).

An SDU may be attached to the house or built inside it: the 9-2-2 definition covers a unit "attached to the single family dwelling", and the rental housing criteria in 8-2A-16(N) say "A single family dwelling may be expanded to create a Second Dwelling Unit". Shared walls must meet the adopted building and fire codes (9-5-4(F)(3)), and each dwelling must have independent HVAC and utility controls (9-5-4(F)(4)). The use is permitted in the same seven districts as the detached form.

Section 9-5-4(F)(2), as amended by Ord. 2662 (7-7-2025), copies the state cap word for word: the unit "shall not exceed one thousand square feet or fifty percent of the size of the single family residence, whichever is larger", with size counted as "the total above grade gross floor area of the dwelling, including any attached garage." The city has not amended this for SF 2369 (effective 7-1-2026), which measures the house by gross living area excluding garages, decks and unheated porches and leaves unfinished basements out of the ADU's size. Counting only above-grade area already leaves basements out, and counting the attached garage in the house's size only raises the 50 percent figure; if the garage clause were read to count a garage in the SDU's own size, the state definition controls. Height and setbacks follow the rules for dwellings in the district; a detached SDU needs 5 feet of separation from other buildings on the lot (9-7-4, note 4).

Neither 9-5-4(F) nor the definition in 9-2-2 requires the owner to live on the property, and Iowa Code 364.3(23)(b)(4) forbids a city from "requiring the property owner to be a resident" or requiring a family or employment relationship between occupants. The rental housing chapter, amended for SDUs by Ord. 2669 (9-15-2025), treats an SDU as a lawful second unit on a single-family lot.

Section 9-5-4(F)(6) says "No additional off-street parking spaces are required for the second dwelling unit", and 9-15-4(A)(2) exempts second dwelling units from providing off-street parking. The one condition is that the new unit cannot make the house fall short of its own parking requirement under Chapter 15, which is what Iowa Code 364.3(23)(b)(3) allows (no parking beyond what a single-family residence needs, and no fee in lieu). Manufactured, mobile and tiny homes used as SDUs need no garage, shed or parking of their own (9-5-4(E)).

Table 5.1 lists the second dwelling as a permitted (P) use, not a permitted conditional use (Pc), so no hearing applies; staff review it through building and grading permits. Section 9-1-8(A)(2)(b) requires a site plan development permit, with findings made by the City Council, for new construction of any P use, but exempts "Single-family residential dwellings" and does not name SDUs. Iowa Code 364.3(23)(c) requires approval "without discretionary review or hearing" on the single-family timeline, so a Council site plan review of an SDU on a single-family lot would be void.

Section 8-2A-16(A) says no one may rent any dwelling unit "on a short- or long-term basis unless they hold a valid rental inspection certificate". This applies to every rental in the city, with inspections about every two years and fees set by Council resolution, and the 8-2A-16(N) criteria expressly allow an SDU on a single-family lot. Section 9-5-4(D) puts short-term rentals (30 days or less) under the same rental housing rules and Iowa Code chapter 423A (hotel and motel tax) "except that no inspection fee shall be charged", which matches Iowa Code 414.1(1)(e): no short-term-rental-specific regulation and no licence or permit fee. Nothing bars separate sale, but an SDU sits on the same lot as the house, and splitting it off would take a subdivision under Title 10.