Can you build an ADU in Portland, OR?
The city’s ADU guidance explicitly allows ADUs in multiple zone categories, including single-dwelling zones, multi-dwelling zones, commercial zones, and EX, subject to Chapter 33.205 and site-specific standards. Feasibility is strongest on lots that already meet minimum lot area and are outside special overlay constraints.
Confidence: high · Last researched May 2026
ADU rules
An accessory dwelling unit is a smaller home on the same lot as the main one and must contain independent living facilities for living, cooking, eating, sleeping, and sanitation. ADUs may be created by internal conversion, addition, conversion of an accessory structure, or new detached construction.
- Allowed as accessory to a house
- May be located within a house
- May be proposed as a manufactured home
- Detached and accessory to a duplex in applicable circumstances
- Detached ADUs are allowed in residential, multi-dwelling, commercial, and EX zones subject to Chapter 33.205
- Minimum lot size requirements apply in RF through R2.5 zones
- For duplex sites in R20 through R2.5, the site must have frontage on a City-maintained street, meet minimum lot size rules, and not be in the Constrained Sites overlay zone ("z")
Dimensional standards in Portland, OR
| R20 — Minimum lot area for one ADU on a lot with a primary structure | 10,000 sq. ft. |
| R10 — Minimum lot area for one ADU on a lot with a primary structure | 5,000 sq. ft. |
| R7 — Minimum lot area for one ADU on a lot with a primary structure | 3,500 sq. ft. |
| R5 — Minimum lot area for one ADU on a lot with a primary structure | 2,500 sq. ft. |
| R2.5 — Minimum lot area for one ADU on a lot with a primary structure | 1,500 sq. ft. |
| R20 — Minimum lot area for one ADU with an attached house | 12,000 sq. ft. |
| R10 — Minimum lot area for one ADU with an attached house | 6,000 sq. ft. |
| R7 — Minimum lot area for one ADU with an attached house | 4,200 sq. ft. |
| R5 — Minimum lot area for one ADU with an attached house | 3,000 sq. ft. |
| R2.5 — Minimum lot area for one ADU with an attached house | 1,500 sq. ft. |
Related questions
Are ADUs allowed in Portland, OR?
An accessory dwelling unit is a smaller home on the same lot as the main one and must contain independent living facilities for living, cooking, eating, sleeping, and sanitation. ADUs may be created by internal conversion, addition, conversion of an accessory structure, or new detached construction.
Full investor analysis
You've seen the general rule. The full Portland, OR report shows which districts allow ADUs by-right vs. by special permit, the approval path and timeline, and the overlay/flood constraints that quietly kill ADU projects here. First town report is free.
Get the full Portland, OR report free →More about Portland, OR zoning
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This summary is AI-generated from public municipal sources and is not legal, engineering, or land-use advice. Always verify zoning with Portland, OR officials before making decisions.
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