Accessory Structures in Clackamas County, OR (2026)
3 rules for unincorporated Clackamas County, Oregon.
Verified from official government sources
ADU Rules
In unincorporated Clackamas County, ZDO Section 839 allows one ADU per single-family dwelling. Inside an urban growth boundary the ADU maxes at 900 sq ft (500 sq ft in R-2.5). Oregon HB 2001 mandates ADUs statewide. Cities set their own rules.
Accessory Dwelling Unit (ADU) Rules in Clackamas County
Some RestrictionsClackamas County ZDO 839.01
Only one accessory dwelling unit shall be allowed per detached single-family dwelling or manufactured dwelling. The maximum floor area of an accessory dwelling unit shall be: 500 square feet in the R-2.5 District; and 900 square feet in all other zoning districts.
ADU Impact Fees
Accessory dwelling units in unincorporated Clackamas County are not exempt from the county's Transportation System Development Charge. Under County Code Section 11.03.020(A), a ZDO-839-compliant ADU is billed at the Institute of Transportation Engineers "220 - Apartment" rate, due before a development or building permit is issued.
ADU Transportation Fee in Clackamas County
Some RestrictionsClackamas County Code Section 11.03.020(A)
ACCESSORY DWELLING UNIT means a unit complying with Clackamas County ZDO 839. Accessory Dwelling Units will be charged the adopted rate for the Institute of Transportation Engineers (ITE) classification of "220 - Apartment." B. AFFILIATE is any entity that directly controls, is controlled by or under common control with the applicant. As used herein, the term "control" or "controlled by" me...
Shed & Carport Rules
In unincorporated Clackamas County, ZDO Section 315 sets accessory-building setbacks. A shed behind the building line under 100 sq ft and 8 feet tall needs no setback; larger sheds need 3-5 ft side/rear setbacks. Sheds over 200 sq ft need a building permit.
Shed and Accessory Building Rules in Clackamas County
Some RestrictionsClackamas County ZDO Section 315, note 11
If an accessory building is located behind the building line of the main building, the applicable minimum rear and side setback standards for that accessory building are based on the accessory building area and accessory building height... 100 square feet or less, 8 feet or less: None.
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