Straight answers
Can you put a tiny house in your backyard in Oregon?
Yes inside most urban growth boundaries, when it is built as an accessory dwelling unit. ORS 197A.425 makes every city of more than 2,500 people and every county of more than 15,000 allow at least one accessory dwelling unit for each detached house, in areas inside the urban growth boundary zoned for detached houses, and the unit can be interior, attached or detached. The city may apply reasonable siting and design rules, but it cannot require you to live on the property or to build extra off-street parking. Outside urban growth boundaries a backyard unit is up to the county, under a narrower statute. The building code changed on 1 January 2026: Oregon's separate Small Home Specialty Code no longer applies, and a sleeping loft in any dwelling now follows Section R332 of the residential code, which requires a fire sprinkler system. A tiny house on wheels is not a building under the code, and whether you can live in one in a backyard is a local rule.
Figures verified against the sources below · October 30, 2026
01 — The longer answer
What Oregon requires, and what your city or county still decides
What the state makes cities and counties allow
ORS 197A.425 applies to cities with more than 2,500 people and counties with more than 15,000. Inside the urban growth boundary, wherever land is zoned for detached single-unit dwellings, they must allow the development of at least one accessory dwelling unit for each detached house. The statute defines that unit as an interior, attached or detached residential structure used in connection with, or accessory to, a single-unit dwelling, so a separate small home in the yard qualifies. Local rules on siting and design still apply, but the statute says reasonable rules do not include an owner-occupancy requirement for either building or a requirement to build more off-street parking. The one exception it keeps: a local government may still require owner occupancy or parking for a unit used as a vacation rental.
Outside the urban growth boundary: a county choice
Rural land is governed by ORS 215.495, and it lets a county allow a backyard unit rather than requiring it. Where a county has opted in, the owner of a lot in an area zoned for rural residential use may build one accessory dwelling unit if the lot is at least two acres, already has one house, and is not in an urban reserve. The unit can have no more than 900 square feet of usable floor area and must stand within 100 feet of the house. It has to meet the sanitation and wastewater rules, the lot must be served by a trained fire protection provider, and the county must have adopted rules on setbacks from resource land and on access for firefighting and evacuation. The unit may not be a vacation rental, the lot may not be divided to separate the two homes, and no second accessory unit is allowed. Subsection (7) says nothing requires a county to allow any of this, so the first call is to the county planning office.
Factory-built homes are sited like site-built ones
Inside an urban growth boundary, ORS 197A.432 requires a local government to allow manufactured homes and prefabricated structures on all land zoned for single-unit dwellings, except in historic districts and on residential land next to a historic landmark. It may not hold a prefabricated structure, or its lot, to any standard that would not apply to a site-built dwelling of the same type on the same land, apart from statewide planning-goal protections and an energy-envelope certification. A separate rule governs the sale: under ORS 455.705(5), a prefabricated structure built on or after 1 July 1991 may not be sold, leased or installed in Oregon unless it carries an insignia of compliance or certification stamp from the Department of Consumer and Business Services. Ask the manufacturer, us included, how a particular unit is approved for Oregon before you order.
Oregon's Small Home Specialty Code no longer applies
Oregon handled small houses differently from most states. In 2019 the legislature adopted the 2018 International Residential Code, including its tiny house appendix, as a separate Small Home Specialty Code for homes of 400 square feet or less, and the residential code sent those homes to it. An amendment to the 2023 Oregon Residential Specialty Code, effective 1 January 2026, struck that sentence and the code's definition of the Small Home Specialty Code, and kept the note that the International Residential Code's tiny house appendix is not adopted in Oregon. In their place it added Section R332, sleeping lofts, which applies to any dwelling, not only a small one. ORS 455.616 still directs the state to keep construction standards for homes of 400 square feet or less that allow sleeping lofts and allow ladders or alternating tread devices as the way down from one.
Sleeping lofts under Section R332
A loft is a sleeping loft under R332 unless it is less than 3 feet deep, smaller than 35 square feet, or has no permanent means of egress. A sleeping loft and the room it opens to must have an automatic sprinkler system to NFPA 13D. Its floor area must be under 70 square feet, its ceiling may not exceed 7 feet over more than half of that area, and it needs at least 3 feet of headroom above its floor and 7 feet of clear height below it. In a sprinklered dwelling a single loft may cover up to two-thirds of the room it is in, if no other loft or mezzanine opens to that room. The way down can be a stair at least 17 inches wide at or above the handrail and 20 inches below it, with risers of 7 to 12 inches; a ladder with rungs at least 12 inches wide, 10 to 14 inches apart, rated for 300 pounds and set at 70 to 80 degrees; or an alternating tread device. A ceiling of at least 3 feet must be kept over the whole width of that way out.
The 2026 residential code, and the tiny house appendix
A new Oregon Residential Specialty Code, based on the 2024 International Residential Code, took effect on 1 October 2026. Its construction chapters and appendices have a six-month phase-in: until they become mandatory on 1 April 2027, either the 2023 or the 2026 code may be used, except Chapter 1. Chapter 1 of the 2026 code lists Appendix BB, the tiny house appendix of the 2024 International Residential Code, among the appendices that are not adopted, are preempted by the state building code and may not be adopted by a local municipality. So no Oregon city or county can bring in the national tiny house rules on its own. The full 2026 code is still being printed, and this page does not claim how its loft rules read until the published text can be checked.
A tiny house on wheels in the backyard
A home on wheels is not a building under the residential code, and the state ADU law above covers a residential structure, so whether you can live in one in a backyard is decided locally. Portland is a worked example of a city that allows it. The owner of a house, attached house or manufactured home may host one occupied recreational vehicle, and a constructed tiny house on a trailer with wheels counts as one. The wheels must stay on, it is not allowed on an undeveloped lot, it must be parked at least 5 feet from the house and not in front of the street-facing facade, it needs a dedicated 20-amp GFCI-protected circuit, any internal plumbing must connect to water and sewer, and it may not be a short-term rental. Portland notes that Oregon DMV may register a tiny house on wheels as a camper, a travel trailer or a park model RV, depending on its size and configuration. Other cities and counties set their own rules, and many have none that allow it.
The honest summary is that Oregon answers the backyard question in state law for most urban lots and leaves rural lots to the county. A small home on a foundation, built as an accessory dwelling unit, is the path the statute protects inside an urban growth boundary, and a factory-built one has to be treated like a site-built one there. What changed in 2026 is the building code: the separate Small Home Specialty Code is gone, sleeping lofts follow R332 with sprinklers, and the national tiny house appendix is closed to local adoption. Check with the city or county for your lot before you order.
03 — Sources
Each figure above links to the authority it came from.
ORS 197A.425 (accessory dwelling units): a city of more than 2,500 or a county of more than 15,000 must allow at least one accessory dwelling unit per detached single-unit dwelling in areas inside the urban growth boundary zoned for detached single-unit dwellings; reasonable siting and design rules exclude owner-occupancy and additional off-street parking requirements; vacation occupancies may still be regulated.
oregonlegislature.govORS 197A.432: inside an urban growth boundary, manufactured homes and prefabricated structures must be allowed on all land zoned for single-unit dwellings and may not be held to standards that would not apply to a site-built dwelling of the same type, with stated exceptions.
oregonlegislature.govORS 215.495: a county may allow one accessory dwelling unit on a lot zoned for rural residential use of at least two acres, of no more than 900 square feet of usable floor area and within 100 feet of the existing dwelling, with the listed conditions; subsection (7) requires no county to allow any.
oregonlegislature.govORS 455.616 (small homes of not more than 400 square feet: standards allowing sleeping lofts and ladders or alternate tread devices) and ORS 455.705(5) (insignia of compliance or certification stamp required to sell, lease or install a prefabricated structure built on or after 1 July 1991).
oregonlegislature.govBuilding Codes Division, 2023 ORSC amendment effective 1 January 2026: strikes the R101.2.1 sentence sending dwellings of 400 square feet or less to the Small Home Specialty Code and its R202 definition; adds the sleeping loft definition and Section R332 (sprinklers to NFPA 13D, area, height and egress rules); Appendix AQ of the 2021 IRC not adopted.
oregon.gov2026 ORSC Chapter 1, effective 1 October 2026: based on the 2024 IRC; R101.2.3.2 lists Appendix BB (Tiny Houses) among matters not adopted, preempted by the state building code and not adoptable by a local municipality.
oregon.govBuilding Codes Division ORSC adoption page: 2026 ORSC construction provisions effective 1 October 2026 with a six-month phase-in, mandatory 1 April 2027; either the 2023 or 2026 ORSC may be used during the phase-in except Chapter 1.
oregon.govCity of Portland: one occupied recreational vehicle or tiny house on wheels allowed on a residential lot with a house, attached house or manufactured home, with the listed placement, utility and rental conditions; Oregon DMV may register a tiny house on wheels as a camper, travel trailer or park model RV.
portland.gov
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