Building an ADU in Oregon: what state law allows

What state law lets you build

Oregon's ADU law says a city with more than 2,500 people or a county with more than 15,000 "shall allow" at least one ADU for each detached single-unit dwelling in areas inside the urban growth boundary zoned for detached houses. The ADU can be "an interior, attached or detached residential structure."

The law was passed in 2017 as SB 1051 and codified at ORS 197.312. In 2025 the Legislature moved it to ORS 197A.425 without changing who it covers. Some state and city web pages still use the old number.

State law sets one ADU as the floor. Many cities allow more, so check your city's code. For one example, see our page on building an ADU in Portland. [1][4][5]

What cities can and can't require

Cities and counties can apply "reasonable local regulations relating to siting and design." That is where size limits, height, setbacks and design rules come from, so those numbers vary by city.

State law says reasonable siting and design rules do not include:

• Owner-occupancy rules for either the ADU or the main house
• Requirements to build additional off-street parking

The one exception is vacation rentals. Cities may regulate ADUs used as "vacation occupancies" and require owner occupancy or off-street parking for them.

Oregon also requires clear and objective standards for housing in most cases, and those standards may not discourage needed housing "through unreasonable cost or delay." [1][6]

Adjustments to setbacks, coverage and design (SB 1537)

A 2024 law, SB 1537, requires cities to grant certain "adjustments" to land use rules for new housing inside urban growth boundaries, and ADUs are on the list. You can ask for up to 10 adjustments in one application. They include:

• Side or rear setbacks, by up to 10 percent
• Parking minimums
• Building lot coverage, by up to 10 percent
• Design standards such as facade materials, roof forms, window materials and garage door orientation

Your application must explain how the adjustments help, for example by making housing feasible or lowering its price. Only you can appeal the decision. A city can apply to the state for an exemption if its own adjustment process meets state tests. These provisions are repealed on January 2, 2032. [7][8]

Middle housing and lot splits

Oregon's middle housing law (HB 2001 of 2019, now ORS 197A.420) requires each county, each city of 25,000 or more people, and each Metro-area city of 1,000 or more to allow all middle housing types on each residential lot. Those types are duplexes, triplexes, quadplexes, cottage clusters and townhouses. Cities of 2,500 to 25,000 outside Metro must allow a duplex on each residential lot.

If you already have a house, or a house plus an ADU, the city must let you keep it and add new middle housing units on the lot. Existing units can be split off from the new units through a middle housing land division.

A 2025 law adds bonus units. If at least one unit is an accessible or affordable unit, a city must allow one more unit for a duplex or triplex, and up to two more for a townhouse, quadplex or cottage cluster. Cities must update their codes for the bonus units by January 1, 2027 (January 1, 2028 for the 2025 changes to cottage clusters).

Middle housing land divisions, under ORS 92.031, let you divide a lot so each middle housing unit can be owned separately, through an expedited process. [2][5][9]

HOA rules and deed restrictions

Under ORS 93.277, a recorded rule that allows a house but bans an ADU allowed under ORS 197A.425, or middle housing, is not enforceable if it was executed on or after January 1, 2021.

Starting January 1, 2027, the law goes further inside urban growth boundaries: such provisions are "void and unenforceable," and the law applies to instruments executed before, on or after January 1, 2021.

HOA rules are covered by a separate law, ORS 94.776. A provision in a planned community's governing documents adopted or amended on or after January 1, 2020, is "void and unenforceable" to the extent it would prohibit or unreasonably restrict housing that the zoning otherwise allows. Starting January 1, 2027, this applies to governing documents adopted at any time, and the law names ADUs and middle housing expressly.

Separate rules in the same laws cover manufactured homes and prefabricated homes. [10][11]

Rural ADUs

Outside urban growth boundaries, counties may choose to allow one ADU on a lot zoned for rural residential use. Conditions include:

• The lot is at least two acres and has one house on it
• The ADU has no more than 900 square feet of usable floor area
• The ADU is no farther than 100 feet from the existing house
• It meets sanitation and wastewater rules, and the lot is served by a qualified fire protection provider

A rural ADU allowed under this law can't be used as a vacation rental, and the county can't let you split it onto its own lot. Counties don't have to allow rural ADUs at all, so check with your county planning office. [12]

Manufactured homes, prefab homes and pre-approved plans

Inside urban growth boundaries, local governments must allow manufactured homes and prefabricated structures on all land zoned for single-unit homes. They can't apply standards that wouldn't apply to a site-built home of the same type, with limited exceptions. Historic districts are excluded. For small homes in a backyard, see our backyard tiny house guide.

A 2025 law (HB 2258) set up "Oregon Homes," a state program of "permit ready" building plans to be preapproved for eligible sites. DLCD and the state Building Codes Division are directed to coordinate on rulemaking to put it in place. Check the DLCD Housing Choice page for updates. [5][13][14]

If your city says no

The Housing Accountability and Production Office (HAPO), created by SB 1537 in 2024, answers questions about state housing laws. You can also report potential violations. Use the HAPO inquiry and complaint form, email DLCD.Hapo@DLCD.oregon.gov or call 503-373-0050.

HAPO says it "will investigate and process complaints consistent with Senate Bill 1537 Section 2." [3][8]

Rules that are still changing

HB 2138 (2025) directs the Land Conservation and Development Commission to adopt rules regulating local development and design standards for middle housing, ADUs and single-room occupancies by January 1, 2028. For background on the permit steps, see our guides to the ADU permit process, ADU costs and ADU financing. [15]

Oregon laws to know

• SB 1051 (2017), now ORS 197A.425

  Requires cities over 2,500 and counties over 15,000 to allow at least one ADU per detached house inside the urban growth boundary. [1][4]

• HB 2001 (2019), now ORS 197A.420

  Requires larger cities to allow middle housing (duplexes, triplexes, quadplexes, townhouses and cottage clusters) and barred owner-occupancy and extra parking rules for ADUs. [2][4]

• SB 1537 (2024)

  Created the Housing Accountability and Production Office and requires cities to grant certain adjustments to development standards for new housing, including ADUs. [7][8]

• HB 2138 (2025)

  Adds bonus middle housing units for accessible or affordable homes, voids older deed and HOA restrictions against ADUs starting January 1, 2027, and directs new state rules for ADU standards. [9][10][11][15]

• ORS 215.495 (rural ADUs)

  Lets counties allow one ADU on rural residential lots of two acres or more. [12]

Questions people ask