Noblesville, IN Accessory Structures: ADU Rules (2026)

Under the City of Noblesville's Unified Development Ordinance, § 159.121(D) lists accessory dwelling units among the accessory uses permitted in every zoning district, subject to the general standards in divisions (B) and (C) plus the ADU-specific rules in paragraph (15). Access may run through a secondary entrance on the property or through the main living quarters under division (a), and the ADU must tie into the principal dwelling's utility service, since division (b) expressly prohibits separate metering. Design review under division (c) requires the unit to be designed to blend with the architectural and exterior appearance of the principal building, and directs that, to the degree reasonably feasible, the property should still read as a single-family residence.

Two further restrictions protect that street presence: division (d) bars any ADU entrance on the front façade, and division (e) bars exterior stairways or similar structures on the front façade. Because an ADU is an accessory structure, it also falls under the general bulk standards in § 159.121(B)(3): combined accessory square footage on a lot of one acre or less is capped at 50% of the principal building's footprint or 1,000 square feet, whichever is less, with larger caps on parcels between one and five acres and on parcels of five acres or more.

A building permit is required under § 159.121(B)(7) unless the structure qualifies for the narrow exemptions in division (C). The Department of Planning and Development reviews ADU applications against all of these design and permitting standards before issuing an improvement location permit.