IA HSB618

Counties and cities must allow at least one accessory dwelling unit (ADU) on any lot with a single-family residence in zoning districts where single-family homes are permitted as a principal use.

ADUs cannot exceed 1,000 square feet or 50% of the primary residence's gross living area, whichever is larger, with unfinished basements excluded from size calculations.

ADUs may only be prohibited or limited by state historic building code restrictions, deed restrictions, or common interest community rules—local governments cannot impose more restrictive regulations on common interest communities than on single-family residences.

Manufactured or mobile homes used as ADUs must be placed on a permanent foundation and converted to real property for tax assessment purposes.

Historic preservation districts may regulate ADUs only if the historic preservation commission determines the unit would be incongruous with the district's historical, architectural, archaeological, or cultural character and documents the reasons for that determination.