What's Required in Portland
- A building permit plus electrical, plumbing and mechanical permits are required to convert space to an ADU or to build a new one.
- An ADU may be no more than 75 percent of the primary dwelling's living area or 800 square feet, whichever is less, except a basement ADU in a house at least 5 years old.
- A detached ADU must be 40 feet from the front lot line or behind the house's rear wall, no taller than 20 feet (15 feet inside a setback), and within the 20 percent accessory-structure coverage cap.
- Detached ADUs over 15 feet must match the house or meet the finish material, 6/12 roof pitch, trim, eave and window standards.
- Fees are valuation-based (ICC Building Valuation Data for new units, 33.3 percent of it for conversions) plus 65 percent plan review, a Development Services fee, a 12 percent state surcharge, a $125 zoning inspection and per-item trade permits.
- System Development Charges apply unless waived through a 10-year covenant barring short-term rentals on the entire property.
- A homeowner cannot do the electrical work on an ADU; a licensed electrical contractor is required, and other contractors need an Oregon CCB license.
- Sites with a slope of 20 percent or more need a geotechnical report, and trees over 12 inches in trunk diameter need protection measures.
- No additional on-site parking is required, and each ADU receives its own lettered address.
Do you need a permit for an ADU in Portland?
Yes. Portland Permitting & Development (PP&D) requires a building permit to convert an attic, basement or garage to habitable space and to build a new accessory dwelling unit, plus electrical, plumbing and mechanical permits, filed with the building permit or later. An ADU can be a conversion, an addition, or a new detached unit. Zoning Code chapter 33.205 caps an ADU at 75 percent of the primary dwelling's living area or 800 square feet, whichever is less, except a basement ADU in a house at least 5 years old. No extra on-site parking is required. In the R20 through R2.5 zones two ADUs are allowed with a house if the lot meets Table 205-2 (3,000 square feet in R5) and fronts a city-maintained street; only one may be attached.
How much does an ADU permit cost in Portland?
Fees are valuation-based plus per-item trade permits. PP&D values a new ADU at the ICC Building Valuation Data figure even if your bid is lower, and a conversion at 33.3 percent of that figure times the area, or your stated value if reasonable. The ICC table is a paid publication, so here is a basement conversion at a stated $60,000: building permit $797.28 for the first $50,000 plus 10 x $6.81 = $865.38; plan review at 65 percent = $562.50; Development Services fee $192.01 plus 10 x $1.88 = $210.81; Oregon 12 percent surcharge $103.85; zoning inspection $125. That is $1,867.53. Trades: a 1,000 square foot wiring package $408 plus 12 percent = $456.96; five plumbing fixtures at $63 = $315 plus 12 percent = $352.80; a heat pump, bath fan, hood and dryer vent total $156, billed at the $167 mechanical minimum plus 12 percent = $187.04. Total about $2,864 before any System Development Charges. For a new detached ADU PP&D publishes a sample at July 2023 rates totaling $36,720.91, of which the four SDCs (sanitary $6,639.20, parks $7,101, transportation $2,941, water $2,281) are $18,962.20; with the SDC waiver the sample drops to about $17,759, still including an $8,070 water service, $748.80 school excise tax and other bureaus' reviews. The 2026 schedules are higher than that sample.
| What you are doing | City filing | Rule |
|---|---|---|
| Basement ADU conversion, stated $60,000 | Building permit plus trades | About $2,864 in PP&D fees including $125 zoning inspection; SDCs may apply unless waived |
| Garage conversion to ADU | Building permit plus trades | Same fee basis; flood-hazard garages may not be convertible |
| New detached ADU on a pre-approved city plan | Building permit plus trades | Free pre-approved plan sets speed review; city sample total $36,720.91 with SDCs, about $17,759 with the waiver |
| ADU rented month-to-month or owner-occupied | SDC waiver available | Sign a 10-year covenant not to use any structure on the property as a short-term rental; 150 percent of SDCs due if revoked |
| ADU intended as an Airbnb-type rental | No SDC waiver | Accessory short-term rentals are not eligible; SDCs are charged in full |
| Detached ADU taller than 15 ft | Building permit with design standards | Must match the house or meet finish, roof pitch 6/12, trim, eave and window standards; 20 ft maximum height |
| Legalizing an ADU built without permits | Building permit | Required; the inspector may order finishes removed to verify hidden work |
What zoning rules apply to a detached ADU?
A detached ADU must be set back 40 feet from the front lot line or sit behind the rear wall of the house. Height is capped at 20 feet, or 15 feet inside a required setback. Its building coverage may not exceed the primary structure's, and all detached accessory structures together may not cover more than 20 percent of the site. Detached ADUs taller than 15 feet must match the house or meet the exterior standards for siding, a roof pitch of at least 6/12, trim, eaves and windows. With two ADUs on a lot, at least one unit must be wheelchair-visitable. A site sloping 20 percent or more needs a soils report, and trees over 12 inches in trunk diameter need protection. Unmet standards require an Adjustment Review of roughly 8 to 10 weeks.
Who can do the work and how do you apply?
Contractors must hold an Oregon Construction Contractors Board (CCB) license listed on the application. A homeowner may sign the building, plumbing and mechanical applications and do that work, but PP&D says you cannot do the electrical work yourself for an ADU. New detached ADUs follow the New Single Family Residence guidelines, and the city offers free pre-approved plan sets. Conversions need a site plan, architectural plans and structural plans if structure changes. Apply through Development Hub PDX (DevHub); the permit issues once checksheets are answered and fees are paid. Email the SDC waiver covenant early to [email protected]. Every permit needs a final inspection.
How to Get a ADU Permit in Portland
Check zoning and the lot
Use the Detached Covered Accessory Structures Worksheet and PortlandMaps to confirm zone, lot size, setbacks, coverage, overlays, flood and slope hazards, and the permit history of the house.
Choose conversion, addition or new build
Conversions follow the ADU and habitable-space code guides; new detached units follow the New Single Family Residence guidelines or a free pre-approved plan set.
Apply on DevHub with trade permits
Submit the building permit application, site plan, architectural and structural plans through Development Hub PDX, with the electrical, plumbing and mechanical applications.
File the SDC waiver and clear review
Email the ADU SDC waiver covenant to [email protected] early. Answer checksheets; the permit issues when all fees are paid.
Build and pass inspections
Install erosion control and tree protection first if required, call 503-823-7000 for each inspection, and get the final approval that starts the 10-year covenant clock.