Accessory Structures in Johnson County, IA (2026)
3 county-level rules, plus city-specific rules for 1 city in Johnson County, Iowa.
Verified from official government sources
ADU Rules
Johnson County treats attached auxiliary dwelling units as an accessory use and detached units as a conditional use in the A, AR, SF, RS, RM, RC, and AG-T districts under UDO Section 8:1.24(E). The county limits each property to one ADU capped at 1,300 square feet or half the primary home's floor area, whichever is smaller, and restricts detached units to parcels of one acre or more.
Johnson County Auxiliary Dwelling Unit Zoning Rules
Some RestrictionsJohnson County UDO 8:1.24(E)
E. Auxiliary Dwelling Unit. Attached auxiliary dwelling units are accessory uses and detached Auxiliary dwelling units are conditionally permitted in the A, AR, SF, RS, RM, RC, and AG-T districts and are subject to the following conditions: ... 2. The net square footage of the auxiliary dwelling unit shall not exceed one thousand three hundred (1,300) square feet of net floor area, or fifty (50...
ADU Owner Occupancy
Johnson County's Unified Development Ordinance allows one auxiliary dwelling unit per property in the A, AR, SF, RS, RM, RC, and AG-T districts, capped at 1,300 square feet or half the primary home's floor area. Whenever the ADU is rented as a short-term rental, the property's legal owner must reside on site.
Johnson County ADU Owner-Occupancy Rule
Some RestrictionsJohnson County UDO § 8:1.24(E)(1),(2),(5)
E. Auxiliary Dwelling Unit. Attached auxiliary dwelling units are accessory uses and detached Auxiliary dwelling units are conditionally permitted in the A, AR, SF, RS, RM, RC, and AG-T districts and are subject to the following conditions: 1. A maximum of one (1) auxiliary dwelling unit may be permitted per property. 2. The net square footage of the auxiliary dwelling unit shall not exceed one...
Shed & Carport Rules
Johnson County's amended building code exempts one-story detached tool sheds and playhouses up to 200 square feet from a building permit, but the shed still must clear the county's accessory-structure setbacks: 60 feet from the right-of-way and either 10 feet from the house or a reduced 5-foot side/rear line.
Johnson County Shed Size, Setback & Permit Rules
Some RestrictionsJohnson County Building Code § 105.2/R105.2(1) (UDO Ch. 8:6.6(B))
105.2/R105.2 Work Exempt from a Permit. A permit shall not be required for the following: Building: 1. One-story detached accessory structures used as tool and storage sheds, playhouses and similar uses, provided the floor area is not greater than two hundred (200) square feet. ... Exemption from the permit requirements of this Code shall not be deemed to grant authorization for any work to be ...
Accessory Structures by City in Johnson County
1 cities in Johnson County have their own accessory structures rules. Each link goes to that city's dedicated page with code citations.
All Johnson County ordinances
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