ADU rules in Multnomah County, OR — also called accessory dwelling unit regulations or granny flat ordinances — cover setbacks, owner-occupancy, parking, and permit requirements.
ADUs are allowed in unincorporated Multnomah County lands within the Urban Growth Boundary under Oregon HB 2001 (2019). ADUs are NOT allowed outside the Urban Growth Boundary. SDC waiver available with 10-year no-STR commitment. Entire-home STR use of ADUs is prohibited.
Multnomah County allows ADUs on single-family residential lots within the Urban Growth Boundary in unincorporated areas per Oregon HB 2001 (2019). ADUs are not allowed outside the UGB where residential development is generally prohibited by state law. Key provisions: SDC waiver available if property owner commits to owner-occupied or long-term rental use for at least 10 years and signs covenant prohibiting STR use of either the ADU or the main house for 10 years. ADU construction does not trigger reassessment of the property's Maximum Assessed Value for property tax purposes. Size, setback, and height standards apply per County Zoning Code Chapter 39. Contact Land Use Planning: 503-988-3043.
Unpermitted ADU: standard building code enforcement. May require legalization or demolition. Occupying unpermitted unit: code violation.
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See how Multnomah County's adu rules rules stack up against other locations.
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