Residential drafting in Portland, Oregon
Portland has the broadest housing stock in the metro. Victorians and early foursquares, a very large body of Craftsman bungalows from the 1905 to 1913 boom, period revival houses in the streetcar neighborhoods, midcentury ranches further out, and steep site custom homes in the West Hills.
Basements are the defining feature for accessory dwelling work here, and Portland's code recognizes that. A basement conversion in a house that has stood at least five years is exempt from the size limit entirely. What decides whether it works is ceiling height, emergency escape, foundation moisture, insulation, stair geometry, and sewer elevation, none of which are visible from a floor plan.
The 50 by 100 foot lot recurs across the inner neighborhoods: house toward the front, narrow side yards, a rear yard or detached garage, alley access in some areas but not all. Mature tree canopy and old sewer routes frequently sit exactly where the new building wants to go.
Detached garages are the other common starting point. They often sit closer to the lot line than a new structure could, and whether that is an advantage depends entirely on their permit history and whether the foundation can carry residential loading.
ADU standards
Setback, size, and parking rules for an accessory dwelling unit in Portland.
| Maximum size | 800 sq ft of living area or 75 percent of the house's living area, whichever is less (33.205.040.C.1) |
|---|---|
| Basement conversion | No size limit when converting a basement in a house that has stood at least five years (33.205.040.C.1) |
| Side and rear setback | 10 ft in RF and R20, 5 ft in R10 through R2.5 (33.110.245.C) |
| Reduced setback | Available in R7, R5, and R2.5 at 15 ft tall or under, with a 24 by 24 ft footprint, no doors or windows facing the line, and screening (33.110.245.C.2) |
| Height, detached | 20 ft, or 15 ft when using the reduced setback (33.110.245.C.1) |
| Lot coverage | All detached accessory structures together may not exceed 20 percent of the site (33.110.245.C.3) |
| Placement | At least 40 ft from the front lot line, or behind the rear wall of the house (33.205.040.C.2) |
| How many | One. Two on a qualifying lot in R20 through R2.5, at least one of which must be detached (33.205.020) |
| Parking | No additional space required (33.205) |
Two accessory units are possible on a qualifying lot in the R20 through R2.5 zones, with a minimum lot area that scales by zone and at least one of the two detached (33.205.020, Table 205-2). That is unusual in this metro and worth checking before assuming one unit is the ceiling.
The Constrained Sites overlay blocks both the two unit option and the duplex plus unit option (33.418.040). That restriction lives in the overlay chapter rather than in the accessory dwelling chapter, which is why it is easy to miss.
Portland waives all city system development charges for a qualifying unit, in exchange for a recorded covenant barring short term rental use anywhere on the property for ten years after final inspection (17.14.070.F). Break the covenant and the charges come due with a recapture penalty. The waiver covers system development charges only. Permit fees and utility connection work are separate.
A detached unit taller than 15 feet picks up design requirements covering roof pitch, siding, trim, street facing windows, and eaves (33.110.245.C). Staying at or under 15 feet avoids them.
Planning office: Portland Permitting and Development
Sources: Portland Zoning Code 33.205, effective October 2024. Portland Zoning Code 33.110.245. Portland Zoning Code 33.418.040. Portland City Code 17.14.070. ORS 197A.425. Last checked August 2026.
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