What are Oregon ADU size and setback regulations?
Last Updated June 24, 2026
In Portland, the maximum size for an ADU is 75% of the living area of the primary structure or 800 sq ft, whichever is smaller. However, if the ADU is in the basement of a primary home that is five years old or more, this limit does not apply. Detached ADUs must be set back 40 feet from the front lot line or behind the rear wall of the primary structure. The side and rear setbacks are zone specific.
Eugene's maximum ADU size is also 800 sq ft. It must be further from the front lot line than the parimary structure, and set back at least 4 ft from the side and read property lines.
In Bend, the maximum ADU size is 800 sq ft as well. The front setback in most residential districts is 10ft, and 4 ft from the side and rear.
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