Cass County, MO Accessory Structures: ADU Rules (2026)

Section 400.030(A)(23), under Limited and Prohibited Uses, states the county's rule for accessory dwellings directly: 'Accessory structures may not be used as a dwelling, except that on a conforming lot which is zoned as Agricultural (A), Rural Residential (R-R) or Rural-Suburban (R-S) a single, transitional living dwelling no larger than nine hundred (900) square feet may be allowed by Special Use Permit.' Outside those three districts, and without a Special Use Permit, converting an accessory structure into a second dwelling on the same lot is not allowed at all.

The Zoning Order's definitions section, Section 400.050, spells out what the county means by a transitional dwelling: it must be 'a single-family accessory dwelling, attached or adjacent to the principal dwelling on the parcel, occupied temporarily by not more than two (2) adult individuals, who, due to human frailty, are in the care and custody of the residents of the principal residence.' The definition makes clear the unit is not a rental: 'Rent may not be charged for this facility,' it may not carry its own mailing address, and its housekeeping facilities are limited to a single bathroom and one kitchen.

The Board of Zoning Adjustment sets the duration of the Special Use Permit, and the intent, per the definition, 'is to accommodate transitional living needs of family members, and not to provide for caretaking facilities' as a business. Because the unit requires a Special Use Permit, the applicant goes through the Planning Board and Board of Zoning Adjustment hearing process, not a simple building-permit counter transaction, and an unpermitted transitional dwelling is enforced as a standard Zoning Order violation, with the same ten-day notice and up to $1,000-per-day Circuit Court fines that apply to other zoning violations under Section 400.030(A)(22).