Everything homeowners ask about building an ADU in Portland — answered with 2026 data.
Yes, ADUs are allowed in All residential zones in Portland, OR. The maximum size for a detached ADU is 800 sq ft or 75% of primary (whichever is less). Attached ADUs can be up to 1,000 sq ft. Portland has an ADU-friendliness score of 9/10. Check our full Portland ADU rules page for complete zoning details.
ADU construction in Portland typically costs $150,000-$300,000. The cost per square foot averages $125-$250. Garage conversions are more affordable at $70,000-$160,000, while prefab ADUs cost $100,000-$240,000. Permit fees add $1,500-$2,500 to your budget. See our detailed Portland ADU cost guide.
Detached ADUs in Portland can be up to 800 sq ft or 75% of primary (whichever is less). Attached ADUs are limited to 1,000 sq ft. Junior ADUs (JADUs) have a cap of 800 sq ft. Maximum height is 20 ft (outside setbacks); 15 ft (within setbacks). You are allowed up to 2 ADUs per lot (1 detached + 1 attached) on a qualifying lot.
Rear setback: 5 feet. Side setback: 0 feet with easement. Front setback: 0 feet (alley lot). Note that garage conversions may be exempt from setback requirements if the existing structure is already within the setback area.
Optional. Many cities and states have been relaxing ADU parking requirements in recent years. In California, no additional parking is required for ADUs near transit.
Not required. Note that owner-occupancy rules vary by state law — California and several other states have eliminated this requirement for standard ADUs.
The ADU permit review timeline in Portland is typically 30-45 days. The plan check process takes approximately 1-2 weeks. Pre-approved plans availability: Extensive pre-approved library available.
Average ADU rental income in Portland: 1-bedroom units rent for $1,400-$1,900/mo/month, 2-bedroom units for $1,800-$2,600/mo/month. Short-term rentals: Yes, with registration. Expected ROI: 6-9% annual return.
The minimum lot size for an ADU in Portland is 3,500 sq ft. This applies to detached ADUs — garage conversions and JADUs may have different or no lot size requirements.
Garage conversions are one of the most popular and affordable ADU options. In Portland, a garage conversion typically costs $70,000-$160,000. The key advantages are lower cost (no foundation work), potential setback exemptions, and faster permitting. Read our complete garage conversion guide.