Springfield, OR Accessory Structures: ADU Rules (2026)

Springfield Development Code section 3.2.275 allows an accessory dwelling unit on any R-1 lot that already has a primary dwelling, with no lot-size threshold for that district. R-2 and R-3 lots are size-gated instead: on an R-2 lot of 6,650 square feet or less, 1 or 2 ADUs are permitted, while a lot between 6,650 and 10,000 square feet must build a minimum of 2, and no ADU at all is allowed on an R-2 lot over 10,000 square feet. The R-3 thresholds are tighter: 1 or 2 ADUs on a lot of 3,200 square feet or less, a minimum of 2 between 3,200 and 4,800 square feet, and none above 4,800 square feet.

Where 2 units are built, at least one must be detached from the primary dwelling. An ADU can be created four ways under section 3.2.275(B): converting an attic, basement, garage, or other part of the existing house; adding floor area including a second story; building a new detached unit; or converting an existing dwelling under 800 square feet into the ADU and building a new primary house. Every ADU is capped at 800 square feet or the primary dwelling's own square footage, excluding its garage, whichever is smaller, must have its own kitchen, bathroom and sleeping area fully independent of the main house, its own separate entrance, its own address, and a hard-surfaced walkway at least 3 feet wide to the street.

Most ADUs go through Type 1 review under section 3.2.275(D); only certain Historic Overlay District cases move to Type 2. Converted ADUs skip the design-matching standards in section 3.2.275(G) unless an exterior change is needed to meet building or fire code.