Boone County, IN Accessory Structures: ADU Rules (2026)

Section 157.063(B) classifies as an accessory dwelling unit any accessory structure with a bathroom, kitchen or living area, and any attached living space with its own separate entrance, such as space above an attached garage, unless the owner files a recorded 'use affidavit' with the Administrator stating the structure will not be used that way. The development-standards table in Section 157.063(C) sets the size band at a 400-square-foot minimum and a maximum equal to the lesser of 1,500 square feet of living area or 50% of the primary dwelling's footprint, limits the county to one accessory dwelling unit per parcel, caps it at two bedrooms, and requires it to match the architectural style of the primary home and meet all applicable building code requirements for a single-family dwelling; manufactured homes qualify only if permanently installed, titled as real property and HUD Code compliant, while RVs and travel trailers are expressly barred.

The unit must sit behind the front facade of the primary dwelling, use the existing driveway rather than a new curb cut, and cannot encroach the 40-foot agricultural setback. Section 157.063(D) requires a special exception before a building permit application, then a building permit covering the legal survey, drainage, elevation, driveway and septic or well permits, plus a deed restriction recorded to keep the standards in effect in perpetuity.