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

072, adopted in 2023, lays out dimensional and general standards meant to keep an ADU secondary to the principal home rather than a second independent dwelling. On the size side, an ADU must measure at least 400 square feet and no more than 800 square feet, or up to forty percent of the principal structure's floor area if that figure is larger, all measured by outside dimensions. The minimum rear setback for an ADU is ten feet, and every other setback must meet the Table A minimums for the principal building, unless the ADU is a conversion of an existing, lawfully built accessory structure.

An ADU can only go on a lot of 5,000 square feet or more, and the code allows the underlying lot coverage percentage in Table A to increase by up to ten percentage points to accommodate it. Only one ADU is permitted per principal residential structure, and it cannot be a shipping container, mobile home, RV, other motor vehicle, travel trailer, or boat. An ADU cannot be built on a vacant lot ahead of the principal structure, though it may go up at the same time as or after the house, and it can straddle a lot line onto an adjoining vacant lot only if both lots share the same owner.

Attached ADUs in the A and R-1 districts must preserve the outward look of a single-family home, while attached ADUs in R-2 must read as a duplex, capped at two front entrances; detached ADUs in A or R-1 must sit behind the principal structure and generally cannot exceed its height. 072(B)(7) also folds it into the county's five-unrelated-person limit on the definition of 'Family,' applying that cap to the whole property, principal home and ADU combined.