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ADU Regulations in Oregon: The Complete Guide
If you’re considering adding an accessory dwelling unit (ADU) to your property in Oregon—or following the modern-day Oregon Trail in search of housing freedom—you’ll be glad to know that this state ranks among the top seven most ADU-friendly in the country. Oregon continues to expand statewide legislation supporting ADUs, and in most areas, they are permitted. In fact, the city of Portland even waives development fees to encourage more homeowners to build.
But just like the pioneers before you, the path to building an ADU in Oregon comes with a few obstacles. While the state is supportive, you still need to meet certain legal requirements, which can vary depending on the city or county where your property is located. Zoning laws, minimum lot sizes, design standards, and permitting rules can all differ, so understanding your local regulations is essential.
The guide below outlines ADU regulations for all 36 Oregon counties. You will find information on size limits, lot requirements, foundation types, and more to help you stay in full compliance with local regulations and forge a new path forward—just like the original settlers in Oregon.
Are ADUs Allowed in Oregon?
Senate Bill 391 took effect on June 23, 2021, establishing statewide permissions for ADUs in Oregon. This builds on earlier ADU legislation by allowing units both within and beyond urban growth boundaries, provided they meet the following criteria:
- Maximum Size: 900 square feet
- Distance from Primary Dwelling: 100 feet
- Minimum Lot Size: 2 acres
Additional criteria related to setbacks and design standards may apply, and enforcement typically falls to city, county, or town officials. While many jurisdictions have adopted the state’s requirements, local standards still vary.
Keep reading to learn what your city or county may require.
ADUs That Are Allowed in Oregon
Under state requirements, ADUs cannot exceed 900 square feet. All of our models are within this limit, with none larger than 848 square feet. The full list is included below.
The A-Frame ADU
571- 848 sq.ft.
1 – 2 Bedroom(s)
1 Bathroom(s)
The Grove ADU
795 sq.ft.
1-2 Bedroom(s)
1-2 Bathroom(s)
The Luna ADU
877 sq.ft.
1-2 Bedroom(s)
1 Bathroom(s)
The Sonoma ADU
672 sq.ft.
1 Bedroom(s)
1 Bathroom(s)
What Is Considered An ADU in Oregon?
In Oregon, various structures can qualify as ADUs, including attached units, detached buildings, and conversions of existing space. To be considered an ADU, the structure must comply with local building codes and applicable requirements. Below, we’ll explore common structure types and explain when each may qualify.
Can Park Model Tiny Homes Be Used As ADUs?
Depending on where you live in Oregon, park model tiny homes may or may not be allowed as ADUs. Some cities and counties permit them, while others do not. Keep reading to find your local requirements and see if your area allows park model tiny homes for this use.
For a broader look at tiny home regulations in Oregon, check out our comprehensive guide to living in one in the state.
Can Cabins From Zook Cabins Be Used As An ADU?
Yes, our modern cabins, log cabins, and luxury mobile homes can be used as ADUs as long as they are under 900 square feet. Below, we’ve highlighted models from each line that meet Oregon’s size requirements. Keep in mind that regulations can vary by city and county, so always check to confirm that your chosen cabin is permitted in your area.
Modern Cabins:
The Woodland
738 – 1440 sq.ft.
2 – 3 Bedroom(s)
1 – 2 Bathroom(s)
Log Cabins:
The Pioneer
650 – 1,700 sq.ft.
2 – 3 Bedroom(s)
1 – 2 Bathroom(s)
The Settler
660 – 1,700 sq.ft.
2 – 4 Bedroom(s)
1 – 2 Bathroom(s)
The Frontier
700 – 1,600 sq.ft.
2 – 3 Bedroom(s)
1 – 2 Bathroom(s)
The Chalet
780 – 1700 sq.ft.
1 – 3 Bedroom(s)
1 – 2 Bathroom(s)
The Musketeer
700 – 1,700 sq.ft.
1 – 3 Bedroom(s)
1 – 3 Bathroom(s)
Luxury Mobile Homes:
The Sonoma
672-875 sq.ft.
1-2 Bedroom(s)
1-2 Bathroom(s)
What is the Difference Between a Prefab ADU & a Modular ADU?
The main difference between these structure types is how they are built and assembled. The chart below breaks down the construction and assembly process for each:
| ADU Type | Off-Site Construction | On-site Assembly |
| Prefab | Fully constructed off-site | Delivered complete; no on-site assembly required |
| Modular | Built in sections off-site | Sections assembled on-site and placed on a permanent foundation |
Check out our comprehensive guide to prefab and modular ADUs to learn more about the differences.
Size & Placement Requirements
One key characteristic of ADUs is their size limitation. Since they serve as secondary dwellings on properties with a primary residence, they must meet specific size and placement standards. Below, we’ll explain those requirements in more detail.
What is the Minimum Size for an Accessory Dwelling Unit?
There is no standard minimum set for ADUs in Oregon, as they likely depend on your building code’s minimum requirements for a dwelling unit. However, according to the Oregon state building code, which many areas have adopted, the minimum size for an efficiency dwelling unit is 190 square feet. So, your ADU can likely not be less than that, but be sure to check with your local officials to ensure compliance with their requirements.
Can My ADU be Bigger Than My House?
No, ADUs typically cannot be larger than the primary dwelling. In most areas, the maximum size is capped at a percentage of the primary home’s square footage. To find out what your local standards are, keep reading.
Do You Need A Permit For An ADU in Oregon?
Yes, a building permit is typically required to add an ADU to your property in Oregon. The specific type and number of permits may vary depending on your location. Keep reading to find your locality’s requirements and the appropriate official to contact for permitting details.
Are There Any Incentives or Grants for ADUs in Oregon?
Yes. While there are no statewide incentives or grants, the city of Portland waives development fees for homeowners building an ADU. This significantly reduces upfront construction costs and makes adding an ADU more financially accessible.
What Features are Included in An ADU from Zook Cabins?
While specific features vary by model, our ADUs offer a range of modern designs with various floor plans, allowing you to select the one that best fits your needs, including:
- Fully finished interiors
- Floor plans featuring multiple bedrooms and bathrooms
- Sizes ranging from 571 to 848 sq. ft.
- Heating & cooling options
- Insulation
- Options for front porches or loft spaces
- Living Areas with plenty of natural light
It’s important to note that certain interior features, such as countertops, tile work, and cabinet colors, can be upgraded to better match your preferences. Talk to your sales representative to learn more about available customization options.
Are Zook Cabin’s ADUs Built to Code?
Yes! Our models are specifically designed to meet local size and room requirements. Because they are modular homes, they must be installed on a permanent foundation to comply with local building codes. Zook Cabins will help you choose the foundation type that best fits your property and meets local requirements.
Can an ADU Have Multiple Bedrooms and Bathrooms?
While some Oregon areas may impose limitations, most allow at least two bedrooms or two bathrooms in an ADU. Explore our Grove, Luna, and A-frame models if you’re interested in a multi-room layout. As always, check with your local officials to confirm the specific requirements in your area.
Are ADUs A Good Investment?
Absolutely. ADUs can be used as rental properties, offering an additional source of income. In some areas, they may even be eligible for separate sale, depending on local subdivision and ownership rules. ADUs can also increase the overall value of your property, potentially boosting resale value when you decide to sell.
What Are the Requirements for ADUs in Each County in Oregon?
Below, we’ve compiled ADU requirements for all 36 counties in Oregon. While many have adopted the state’s standards, some counties enforce their own. Keep in mind that cities and towns can also set their own rules. If you live within city limits rather than an unincorporated area, skip ahead to find out what your city or town allows.
Does Baker County Allow ADUs?
The county zoning ordinance does not mention ADUs, making it unclear if they are permitted. They likely allow them if they adhere to the Oregon Residential Specialty Code.
Does Benton County Allow ADUs?
Yes, but ADUs must meet the following development standards:
- Maximum Size: 900 square feet
- Maximum Number of Bedrooms & Bathrooms: 2
Your ADU must comply with additional development standards. Consult with the Community Development Department to ensure your plans comply with Benton County’s requirements.
Does Clackamas County Allow ADUs?
Yes, but in order to be approved, your ADU must meet the following requirements:
- Recreational vehicles or park model tiny homes can be used as ADUs in certain urban and rural residential areas
- Maximum Size
- R-2.5 District: 500 square feet
- All other zoning districts, except the VR–⅘, VR-5/7, and VTH: 900 square feet
Because standards can vary by zoning district, it’s recommended that you contact Development Services to certify compliance with all applicable requirements.
Does Clatsop County Allow ADUs?
Yes, but there are specific sizing requirements you must meet, including:
- Maximum Size: 900 square feet or 75% of the gross habitable floor area (GHFA) of the primary dwelling, whichever is less
Additional requirements apply, including setbacks that vary by zoning district. Consult the Community Development Department to ensure your plans meet all applicable standards.
Does Columbia County Allow ADUs?
The county does allow ADUs, but there are specific requirements in place to add one to your property:
- Maximum Size: 1,200 square feet, or whatever your city requires
- Minimum Size: Must conform to your zoning district’s requirements
If you live in a city or town, consult with local officials. If you live in an unincorporated area, contact the Building Department to ensure compliance with all requirements.
Does Coos County Allow ADUs?
ADUs are permitted in Coos County, so long as they follow these requirements:
- Maximum Size:
- Residential Zones: 900 square feet
- Urban Zones: 800 square feet or 75% of the primary dwelling’s floor area, whichever is smaller
- Minimum Lot Size: 2 acres
Because zoning regulations, such as permissions and setbacks, can vary by district, contact the Community Development Department to confirm your plans meet all applicable requirements.
Does Crook County Allow ADUs?
Yes, but they must meet the following standards as outlined by SB 391:
- Maximum Size: 900 square feet
- Minimum Lot Size: 2 acres
Some requirements, such as setbacks, still vary by zoning district. Consult with the Community Development Department to ensure your ADU plans meet all applicable design standards.
Does Curry County Allow ADUs?
Yes, but there are specific requirements you must meet depending on your location within the county. These requirements are as follows:
- Inside Urban Growth Boundary
- Maximum Size: 1,200 square feet
- Minimum Size: 240 square feet
- Distance from Primary Dwelling: 20 feet
- Outside Urban Growth Boundary
- Maximum Size: 900 square feet
- Distance from Primary Dwelling: 20-100 feet, no more and no less
- Minimum Lot Size: 2 acres
Since requirements vary depending on where you reside, be sure to consult with the Community Development Department to ensure compliance with the standards for ADUs in your area.
Does Deschutes County Allow ADUs?
Yes, ADUs are allowed in Deschutes County with an approved permit. To receive approval, your application must meet the following requirements:
- Maximum Size: 900 square feet
- Minimum Lot Size: 2 acres
If you have any questions or want more information on requirements, contact the Community Development Department.
Does Douglas County Allow ADUs?
You can have an ADU in Douglas County, but it must meet the following requirements:
- Minimum Property Size: 2 acres
- Maximum Size: 900 square feet
- Number of ADUs Per Lot: 1
Additional requirements apply, including setbacks, which can vary by zoning district. Consult with the Planning Department to ensure compliance with all applicable standards.
Does Gilliam County Allow ADUs?
They may be permitted under SB 391, but specific information regarding ADUs in the county is unavailable. Contact the Planning Department for clarification on what they allow.
Does Grant County Allow ADUs?
It is unclear from their land development code whether they are permitted to do so. However, they may be allowed under the provisions of SB 391. Contact the Planning Department to determine if this is the case.
Does Harney County Allow ADUs?
It is unclear if they are allowed, as the zoning ordinance only mentions accessory dwellings on agriculturally zoned properties. However, they may be permitted as a result of SB 391. To find out if this is the case, contact the Community Development Department.
Does Hood River County Allow ADUs?
Yes, provided that they meet the following requirements:
- Maximum Size: 800 square feet
There are additional requirements regarding setbacks, but these can vary depending on your zoning district. Contact the Planning & Zoning Department to learn more about the requirements specific to your area.
Does Jackson County Allow ADUs?
Yes, ADUs are permitted in Jackson County so long as they adhere to the following standards:
- Maximum Size: 900 square feet
- Distance from Primary Dwelling: 100 feet
Additional requirements are in place, but can vary depending on your zoning district. Contact the Building Division to ensure compliance with all applicable regulations.
Does Jefferson County Allow ADUs?
ADUs are permitted in Jefferson County, subject to the following requirements under SB 391:
- Maximum Size: 900 square feet
- Distance from the Primary Dwelling: 100 feet
- Minimum Lot Size: 2 acres
Other requirements vary by zoning district, so be sure to consult with the Community Development Department to ensure compliance with all applicable ADU standards.
Does Josephine County Allow ADUs?
Yes, as long as the ADU meets state requirements, including the 900-square-foot maximum. For help confirming local zoning requirements, contact the Community Development Department.
Does Klamath County Allow ADUs?
Yes, provided that they meet the following standards:
- Maximum Size: 800 square feet or 50% of the floor area of the primary dwelling, whichever is less
- Number Per Lot: 1
ADUs in Klamath County must meet additional development standards including height and setbacks. To certify compliance with these requirements, contact the Community Development Department.
Does Lake County Allow ADUs?
Lake County has adopted the Oregon Specialty Code, which allows ADUs under the state’s requirements, as long as the unit does not exceed 900 square feet. Contact the Building Department to confirm that your plans meet all applicable ADU regulations.
Does Lane County Allow ADUs?
Yes, as long as they meet the requirements of SB 391, including the 900-square-foot size limit. Contact the Building Safety Department to ensure compliance with all applicable regulations.
Does Lincoln County Allow ADUs?
The county code does not directly mention ADUs, but they may be permitted under SB 391’s provisions. Contact the Building Division to find out if this is the case.
Does Linn County Allow ADUs?
Yes, so long as they meet the following requirements:
- Number Per Lot: 1
- Maximum Size: 800 square feet
- No park model tiny homes allowed as ADUs
- Permanent Foundation: Required
To obtain the required building permit or to learn more about setback, height, and other ADU requirements, contact the Planning & Building Department.
Does Malheur County Allow ADUs?
The county code does not specifically outline requirements for ADUs, so it’s unclear how they are addressed locally. However, they may be allowed under state regulations. Contact both the Building and Planning Departments to confirm compliance with all applicable requirements.
Does Marion County Allow ADUs?
Yes, provided they adhere to these development standards:
- Maximum Size: 900 square feet or 75% of the footprint of the main dwelling, whichever is less
Additional standards apply, but they vary depending on the type of ADU you plan to build and the zoning district where it’s located. Contact the Public Works Department to ensure compliance with all applicable requirements.
Does Morrow County Allow ADUs?
Accessory dwelling units are not mentioned in the county zoning ordinance, but may be permitted under SB 391’s provisions. Contact the Planning Department to determine if this is the case.
Does Multnomah County Allow ADUs?
Yes, provided that:
- Maximum Size: 800 square feet or 75% of the floor area of the single-family dwelling, whichever is less
- Park model tiny homes are not used as an ADU
Additional requirements are likely in place regarding setbacks, height, and more. Be sure to contact the Land Use & Planning Division to ensure compliance.
Does Polk County Allow ADUs?
Yes, so long as they meet the following criteria:
- Maximum Size: 900 square feet or 75% of the main dwelling’s perimeter area, whichever is less
- Maximum Height: 25 feet
ADUs must meet both the state building code requirements for residential structures and the development standards of your zoning district. Contact the Community Development Department to learn which regulations apply to your property.
Does Sherman County Allow ADUs?
The county zoning ordinance does not specifically address ADUs, so their status is unclear. However, they may be allowed under state requirements. Contact the Planning Department to confirm what is permitted.
Does Tillamook County Allow ADUs?
ADUs are permitted in Tillamook County, so long as:
- Maximum Size: 800 square feet or 75% of the living space of the primary residence, whichever is less
- Park model tiny homes are not used as ADUs
Additional requirements related to size, placement, and other design factors may apply and can vary by zoning district. Consult the Community Development Department to ensure your plans meet all applicable standards.
Does Umatilla County Allow ADUs?
Yes, but specific requirements are unclear. The county likely adheres to the standards set forth in SB 391, but to determine if this is the case, contact the Planning Division.
Does Union County Allow ADUs?
ADUs are permitted in residential zones only in Union County, provided that:
- Maximum Size: 900 square feet
Additional requirements may apply and can vary by zoning district. Contact the Planning Department to ensure your plans meet all applicable standards.
Does Wallowa County Allow ADUs?
Yes, but specific requirements must be met, including:
- Maximum Size: 900 square feet
- Only one recreational vehicle or park model tiny home per lot
ADUs in Wallowa County must meet all other applicable development standards, including height, setbacks, lot coverage, and more. Contact the Building Codes Department to ensure compliance with all relevant regulations.
Does Wasco County Allow ADUs?
Yes, so long as your ADU meets the following requirements:
- Minimum Lot Size: 6,000 square feet
- Maximum ADU Size: 1,200 square feet
Additional standards regarding setbacks, height, and other building code requirements must be met. To ensure compliance with these standards, connect with Building Code Services.
Does Washington County Allow ADUs?
Yes, Washington County’s ADU requirements are as follows:
- Maximum Size: 800 square feet
- Setback Requirements:
- Side Yard Setback: 5 feet
- Rear Yard Setback: Based on the zoning district
- Front Yard Setback: Depends on the zoning district
Because requirements can vary by zoning district, ensure compliance with all applicable standards with Building Services.
Does Wheeler County Allow ADUs?
ADU permissions are unclear, as no legislation explicitly addresses them at the county level. However, they may be allowed under state requirements, with specifics varying by the city or town where you live.
Does Yamhill County Allow ADUs?
Yes, provided the following standards are met:
- Maximum Size: 900 square feet or 75% of the primary dwelling’s floor area, whichever is less
- Maximum Height: 25 feet
- Setbacks: Vary by zoning district
In addition to these standards, all applicable setbacks, building codes, and other local requirements must also be met. Contact the Planning & Development Department to confirm compliance.
Find Your Accessory Dwelling Units Requirements in Oregon By Municipality
| City | Department | Allows ADUs | Minimum Size | Maximum Size |
| Eugene | Planning & Development Department | Yes | No minimum | 800 sq ft or 10% of the lot area |
| Gresham | Urban Design & Planning Department | Yes | Not specified | 900 sq ft |
| Hillsboro | Community Development Department | Yes | 250 sq ft | 750 sq ft |
| Portland | Zoning & Land Use Department | Yes | Not specified | 75% of the main structure or 800 sq ft |
| Salem | Land Use & Zoning | Yes | Not specified | 900 sq ft or 75% of the main house |
| Turner | Planning & Building Department | Yes | Not specified | 800 sq ft, or the size of the primary dwelling |
Does Eugene Allow ADUs?
Yes, the city does permit ADUs in all neighborhoods, provided that:
- Maximum Size: 800 square feet or 10% of the lot area in most zones, whichever is smaller
- Owner Occupancy: Not required for either unit
- Must meet ADU design standards, but no other residential design standards are required
If you have any questions or want to ensure your ADU plans are approved, contact Eugene’s Planning & Development Department.
Does Gresham Allow ADUs?
The city does permit ADUs, but they must meet the following standards:
- Park model tiny homes, or THOWs, are not permitted as ADUs
- Maximum size: 900 square feet
Detached ADUs must meet specific design requirements, which you must submit with your permit application. Contact the Urban Design and Planning Department beforehand to improve your chances of getting approval.
Does Hillsboro Allow ADUs?
ADUs are allowed in Hillsboro if they meet these requirements:
- Minimum Size: 250 square feet
- Maximum Size: 750 square feet
Additional requirements may also need to be met. Reach out to the Community Development Department to ensure compliance.
Does Portland Allow ADUs?
Yes, but the city outlines the following standards for them:
- Maximum Size: 75% of the living area of the main structure or 800 square feet, whichever is smaller
Additional standards vary by zoning district. Consult with the Zoning & Land Use Department to determine which requirements apply.
Does Salem Allow ADUs?
Yes, and the defining traits of ADUs in the city include:
- Maximum Size: 900 square feet or 75% of the main house, whichever is less
- Maximum Height: 25 feet
- Number of ADUs per Property: 1
To ensure compliance with all applicable requirements, contact the Land Use & Zoning Department.
Does Turner Allow ADUs?
Yes, up to 1 ADU is permitted per lot, provided that:
- Maximum Size: 800 square feet or no larger than the square footage of the primary dwelling
- Minimum Lot Area: 6,000 square feet
Other requirements regarding size, design, and setbacks are in place. Be sure to consult with the Planning & Building Department to ensure your ADU plans will be approved.
Searching For An ADU Builder Serving Oregon?
Now that you have a clear understanding of the requirements for ADUs in Oregon, the next step is to find a builder that serves your area. Because Oregon has specific regulations, it is important to choose a builder who:
- Offers ADUs that do not exceed 900 square feet
- Complies with local building codes and permitting requirements
- Provides layouts with multiple bedrooms and bathrooms that meet your locality’s standards
At Zook Cabins, we kept these criteria in mind when designing our ADU line. All of our models are 848 square feet or less, staying well within Oregon’s maximum size limits. We also work closely with you to ensure all permitting and building code requirements are met.
You’ll have plenty of options to choose from. Our Grove, Luna, and A-frame models all offer layouts with one or two bedrooms or bathrooms. In addition, our Sonoma luxury mobile home and many of our modern and log cabins, including the Pioneer and the Settler, meet Oregon’s standards, making it easy to find the right fit for your property.
If you have questions or are ready to get started, request a quote or contact one of our sales representatives today.
Tiny Home & ADU Rules By State: See How They Compare?
When it comes to affordable housing, ADUs aren’t the only option. Tiny homes are another popular choice. However, the line between the two can be blurry, making it difficult to tell whether a tiny home qualifies as an ADU or if an ADU is always considered a tiny home. To clear up the confusion, we’ve created this clear-cut guide comparing ADUs and tiny homes.
Because requirements for both can vary widely within a single state and across the U.S., we’ve also compiled a list of ADU and tiny home regulations by location. This will help you understand what each area allows and which type of structure might be the best fit for your needs.
Check out the chart below to start exploring.