Oregon ADU Laws, Costs & Permit Guide (2026)
Oregon requires cities over 2,500 residents to allow ADUs on all single-family lots. Portland has some of the most developed ADU ecosystems in the country.
Oregon ADU At a Glance
Permit Timeline
90–150 days
Average Build Cost
$130,000 – $280,000
Maximum Size
900 sq ft or 75% of primary home
Owner-Occupancy Required
Varies by city (Portland: not required)
Impact Fees
Varies by city; Portland waives SDCs for some ADUs
Setbacks
Varies; Portland allows 0 ft rear setback in some zones
Recent Law Changes in Oregon
Required all Oregon cities with 2,500+ residents to allow duplexes and ADUs on single-family lots as a matter of right.
Find ADU Contractors in Oregon
Browse vetted builders, architects, permit expediters, and ADU lenders serving Oregon homeowners.
Browse Oregon Contractors →Frequently Asked Questions — ADUs in Oregon
Is an ADU allowed on my property in Oregon?
If you live in a city with more than 2,500 residents, state law (HB 2001) requires your city to allow at least one ADU on your single-family lot. Rural areas may have different rules.
How much does it cost to build an ADU in Oregon?
Oregon ADU costs typically range from $130,000 to $280,000 for a detached unit. Portland tends to run on the higher end. Garage conversions and basement ADUs are often less expensive.
Does Portland waive system development charges (SDCs) for ADUs?
Portland has historically waived SDCs for ADUs under certain conditions. Check with the Bureau of Development Services for current policy, as this changes periodically.
Sources
Disclaimer: The information on this page is provided for general informational purposes only and does not constitute legal, financial, or construction advice. ADU regulations change frequently — always verify current rules with your local planning department and consult a licensed professional before making decisions. ADUHomeResource.com is not liable for any errors, omissions, or outcomes resulting from use of this information.