West Des Moines, IA Accessory Structures: ADU Rules (2026)

Zoning section 9-5-4(F) treats a second dwelling unit as exempt from the maximum density table in section 9-7-4 even though the lot must still meet the minimum bulk regulations, including lot size and setbacks, for its single-family zoning district. The unit is capped at one thousand square feet or fifty percent of the size of the single-family residence, whichever is larger, and that size calculation counts the total above-grade gross floor area including any attached garage. It may be attached to the primary dwelling, freestanding, or incorporated into an accessory building such as a detached garage, but any shared wall must meet the City's building and fire protection requirements.

The two dwellings cannot share heating, cooling, or ventilation systems and must each have independent control of HVAC, electricity, communications, and water, although they may share utility service lines from the main if metering and maintenance can be handled. Each unit needs its own entry with direct access to a street. No additional off-street parking spaces are required for the second unit, but adding it cannot push the original dwelling below the parking requirements in Title 9, Chapter 15. Where the ADU takes the form of a manufactured or modular unit, it must sit on a permanent foundation visually compatible with surrounding homes and is exempt from the garage requirement that otherwise applies under subsection 9-10-4B.