Guides / ADUs · Updated
What Oregon lets you build as an ADU
From the Oregon Revised Statutes (2025 edition), ORS 197A.425 and 215.495, checked November 2026.
Short answer
In an Oregon city of more than 2,500 people, or a county of more than 15,000, you can build at least one ADU with each detached house inside the urban growth boundary. The city can't make you live on the lot or add parking. Size, height and setbacks are local, so your city's code sets them. Out in rural residential zones, a county may allow one ADU of up to 900 sq ft on 2 acres or more.
Inside the urban growth boundary
| Rule | What the law says | ORS |
|---|---|---|
| Who must allow them | Cities of more than 2,500 people and counties of more than 15,000, in areas inside the urban growth boundary zoned for detached houses | 197A.425(1)(a) |
| How many | At least one ADU for each detached house | 197A.425(1)(a) |
| What counts | An interior, attached or detached unit used with a single-unit dwelling | 197A.425(1)(b)(A) |
| Size, height, setbacks | Not set by the state: left to “reasonable local regulations relating to siting and design” | 197A.425(1)(a) |
| Owner-occupancy | Can’t be required, for the house or the ADU | 197A.425(1)(b)(B) |
| Parking | No requirement to build more off-street parking | 197A.425(1)(b)(B) |
| Vacation rentals | A city may require owner-occupancy or parking for vacation occupancies | 197A.425(2) |
Oregon's middle housing law reaches further on many lots: each county, each city of 25,000 or more, and each city of 1,000 or more inside Metro (Portland's regional government) "shall allow the development of all middle housing types on each lot or parcel zoned for residential use", and other cities of 2,500 to 25,000 must allow a duplex (ORS 197A.420(2)–(3)).
Rural ADUs (ORS 215.495)
| Rule | What the law says |
|---|---|
| Who decides | Optional: a county may allow one ADU on rural residential land |
| Lot size | At least 2 acres, not in an urban reserve, with one house on it |
| Size | No more than 900 sq ft of usable floor area |
| Where on the lot | No farther than 100 ft from the house |
| Renting | Can’t be used as a vacation rental |
| Splitting off | The land can’t be divided to separate the ADU from the house, and no second ADU |
The law lists more conditions: sanitation and water supply, fire protection and access for firefighting, and setbacks. "Nothing in this section requires a county to allow any accessory dwelling units in areas zoned for rural residential use" (ORS 215.495(7)), so check your county.
In the law's words
A qualifying city or county "shall allow in areas within the urban growth boundary that are zoned for detached single-unit dwellings the development of at least one accessory dwelling unit for each detached single-unit dwelling, subject to reasonable local regulations relating to siting and design" (ORS 197A.425(1)(a)).
Those regulations "do not include owner-occupancy requirements of either the primary or accessory structure or requirements to construct additional off-street parking" (ORS 197A.425(1)(b)(B)).
See it on your lot
Portland-area property lines are on the measuring map (Multnomah, Washington and Clackamas counties), so you can place an ADU and see the room it leaves. Price it with the ADU cost calculator, and see six ready-made ADU floor plans. Other states: California, Washington. Texas has no statewide ADU law; a 2025 bill (SB 673) passed the Senate but not the House.