Understanding Ithaca's 2025 ADU Ordinance: What Homeowners Need to Know

In May 2025, the City of Ithaca passed a landmark Accessory Dwelling Unit (ADU) ordinance, establishing the right to build ADUs in several residential zones throughout the City. For homeowners, this opens up new opportunities to add housing, generate rental income, and accommodate family members — all while maintaining neighborhood character.

An ADU is a smaller, secondary dwelling unit located on the same lot as a primary structure. It can be attached to the primary structure (basement, attic, addition, or garage) or detached within an approved accessory structure such as a garage, carriage house, or cottage.

The ordinance permits ADUs in the R-1, R-2, and R-3 residential zones, each with its own lot-size minimums and placement flexibility. R-1 (low-density) requires the largest lots, while R-3 (higher-density) offers the most flexible ADU regulations.

Key requirements include a maximum ADU size of roughly 800–1,000 sq ft (or up to 50% of the primary dwelling's floor area, whichever is less), rear and side setbacks of 5–10 feet, and height limits of 20–25 feet. Parking requirements are reduced or waived in most zones, especially near transit.

All ADUs must adhere to building code regulations for safety. The City is currently developing a homeowner guide and approved template ADU plans to streamline the process. If you're considering an ADU, the first step is confirming your property's zoning district and reviewing the applicable requirements.