An accessory dwelling unit (ADU) is an additional dwelling unit created on a lot with a house, attached house, tiny house, duplex, or manufactured home. The second unit is smaller than the main dwelling. You can create an ADU by:
- Converting part of the existing house
- Converting an existing garage or
- Constructing a new building
You'll need building and trade (electrical, mechanical and plumbing) permits for this project
A building permit is required to convert attics, basements, or garages to living or habitable space.
You also need a building permit to build a new ADU. The City of Portland offers pre-approved building plans for detached ADUs that can be submitted with a building permit application. More information about pre-approved plans is provided in Step 2 below.
Your ADU project will also require trade (electrical, plumbing, and mechanical) permits. You may apply for these trade permits at the same time as your building permit, or you may apply and pay for trade permits later. Applying for trade permits with the building permit application provides the benefit of combining all the permits under one permit number, but trade permits can be applied and paid for later in the process.
Check with your county assessor on likely property tax impacts
Adding an accessory dwelling unit will likely increase the value of your home, and thus its property taxes, significantly. The value on which property taxes are assessed is determined by a county assessor, not by the City of Portland.
Before starting your ADU project, please contact your county assessor’s office to learn how the addition of an ADU may affect your property taxes.
Multnomah County provides a web page with more information on how ADUs can affect property taxes. For homes located within the City of Portland but outside Multnomah County, please contact your county assessor’s office to learn more about how your property taxes may be affected:
Evaluating existing space to convert to an ADU
Constructing an ADU within your existing home may be an option. However, you should be aware that unfinished areas inside your home may not meet current building code requirements for living space. This includes:
- Ceiling height
- Emergency egress windows (emergency exit windows)
- Insulation and Ventilation
- Stairs
These conditions could make it expensive, difficult, or even impossible for you to convert existing space into an ADU. Researching your property, as described below, can help identify whether these limitations are present for your property.
Step 1: Research your property before you build an ADU
Check the permit history for your house
Depending on the age of your house, we may have inspection cards or microfilmed plans that show the permit history for your house. It is important to verify the permit records, not rely on the tax information from the county assessor’s office. If an "existing” finished attic or basement was not permitted, it will need to be legalized through the new permit as if the work was not already done.
Some records are available online. Visit our public records web page to request permit records for your home.
Find out about the zoning standards for an ADU
There are a variety of use and design standards in the zoning code that apply to the creation of an ADU. These include:
- Restrictions on short-term rentals and home occupations
- Limits on the size of the ADU
- Design requirements for new detached ADUs over 15 feet tall
The zoning code determines how close detached ADUs can be built to property lines and how many structures can be built on a lot. This worksheet describes the zoning rules for detached accessory structures like ADUs.
Learn how to research the zoning of your property.
For detailed information on the zoning code standards such as visibility and height allowances, click here.
Learn about required city utility connections
The ADU and the primary dwelling unit shall have separate and independent water supply and sanitary sewer systems, except as allowed by Water and Environmental Services.
Get more information on water and sewer requirements such as decommissioning a septic tank or cesspool, numbers of allowable fixtures, and shared and separate meters.
Research Flood Hazard and Slope Hazard Areas
Specific requirements and limitations apply to development within flood hazard areas, on sloping sites, and sites within the mapped landslide inventory area. For example, converting a garage located in a flood hazard area may not be allowed. Development on sites with slopes of 20% or more or within a mapped landslide inventory area will require a geotechnical engineering (soils) report.
Please schedule a free 15-minute appointment with a Building Code and Engineering Reviewer with Site Development for more information.
To determine if your property is in a flood hazard area please refer to the maps and instructions on this web page. Environmental Services also provides helpful information for protecting your property if it is in a floodplain. To determine if your property is in a steep slope (20% or greater) area or within a mapped landslide inventory area, please visit Portland Maps to search by address and review the Hazard section of the Public Safety tab.
Learn about construction standards
Construction of new accessory dwelling units and additions to existing single-family dwellings to create an accessory dwelling unit must comply with the requirements of the Oregon Residential Specialty Code (ORSC) for one- and two-family dwellings. Alternative construction standards, listed in the Accessory Dwelling Unit Code Guide, apply when an accessory dwelling unit is created within an existing single-family dwelling unit or within an existing detached accessory structure such as a garage.
Accessory dwelling units may be added to townhouses, which are considered a single-family dwelling unit, if the townhouse structure meets the requirements of Building Code Guide 19-11: Townhouses. Accessory dwelling units may not be added within an existing two-family dwelling unit unless the structure is modified to meet the requirements of the Oregon Structural Specialty Code (OSSC) or unless the existing dwelling units are redesigned to meet the requirements of townhouses. Note: The Accessory Dwelling Unit Code Guide does not apply to structures reviewed under the OSSC.
Who can do the work?
Contractors must have a license to work in Oregon. The Oregon Construction Contractors Board (CCB) issues licenses to contractors. The permit application and their company materials must list the license number. Need help finding a contractor? The CCB website has good tips on how to search for one. Plumbing and Electrical contractors have additional license requirements.
If you are a homeowner doing the work yourself, then you can sign the building and trade permit applications. You cannot do the electrical work yourself for an ADU. You must hire a licensed electrical contractor to do the electrical work on an ADU. The State of Oregon has some helpful information for homeowners:
Fees and System Development Charges
The development of an ADU requires building permit fees, water service fees and System Development Charges (SDCs). In some instances, fees or SDCs can be substantial. Fees and SDC charges are based on the information below.
Building permit fees
Permit fees are based on the type of permit, the work proposed, the valuation of the work, and the staff that needs to review the work. When you create a new dwelling unit, system development charges are usually charged.
System Development Charges
The construction of detached ADUs or the conversion of existing structures to ADUs is typically subject to System Development Charges (SDCs) that are levied by the Portland Parks and Recreation, Environmental Services, Transportation, and Water bureaus.
Transportation SDCs
For ADUs where the SDC is not waived, the Bureau of Transportation charges an SDC.
Environmental Services SDCs
For ADUs where the SDC is not waived, the Bureau of Environmental Services charges an SDC. The amount of the SDC will be based on fees that were paid previously and the addition of an ADU based on the current sewer connection charge.
In some cases, it may be necessary to increase the size of the sewer or wastewater line or to provide the ADU with a separate connection to the sanitary sewer system. In these cases, additional fees will be required even if SDC charges are waived.
Parks and Recreation SDCs
For ADUs where the SDC is not waived, Portland Parks and Recreation charges an SDC for the creation of any ADU. Please call Parks and Recreation for the current rate.
Water Bureau SDCs
The Water Bureau does not automatically charge an SDC when an ADU is constructed. If the ADU can be added without changing the size of the existing water service, there is no charge. Click here for more information about connecting to city utilities. Upon request, the Water Bureau can verify the existing water service size. If an increase in water service is required, then there is a charge for increasing the service along with the differential cost increase for the larger service. Please contact the Water Bureau for more information.
ADU SDC waiver program
You may be eligible to apply for an SDC waiver. Learn more about this program.
Step 1b: Still need help? Schedule a 15-minute appointment
This is an optional step. If you still need help, we are here for you if you have questions about the information and materials you need to apply. You can schedule a free 15-minute appointment with any of these reviewers:
- Meet with a City Planner to receive information about Zoning and Tree Code requirements that apply to your property.
- Meet with a Building Code and Engineering Reviewer to get help with building code, engineering and site development requirements.
- Meet with a Permit Technician if you have questions about the permit process or if you need help with application requirements.
- Meet with a Water expert to find out if your project requires you to increase the size of your existing water meter.
- Meet with a Transportation expert to find out if your project will trigger right-of-way improvements.
- Meet with a Sewer and Stormwater expert to find out if upgrades to your sewer service will be needed.
If you need help, these are experts we recommend you meet with for your ADU project. Not all review groups are listed. The groups listed above will help get you started.
Step 2: Prepare an ADU building permit application and required forms and documents
All construction projects require a site plan.
New detached ADUs
If you plan to build a new detached ADU, follow the New Single Family Residence guidelines. You may also submit one of the free plans provided below that are pre-approved for Life Safety and Structural requirements of the Oregon Residential Specialty Code.
These pre-approved plans were provided by the City of Eugene, with minor changes. The City of Eugene shared its developed plans with the City of Portland at no cost.
You are not required to submit a pre-approved plan for a detached ADU, but these plans are free and can save time in receiving your building permit. These pre-approved plans are not suitable for all lots.
There are four options of this free plan to choose from that vary in roof and foundation type:
An ADU with a gable roof and concrete slab on grade floor and foundations
An ADU with a shed roof and concrete slab on grade floor and foundations
An ADU with a gable roof and wood-framed floor and crawl space
An ADU with a shed roof and wood-framed floor and crawl space
Please note that if you select the shed roof option or include a cover over the concrete landing by the front door, the ADU will not meet the size limits to be built within side and rear setbacks. The size of side and rear setbacks starts at five feet, but they may be larger depending on the property’s zoning.
The bathroom on the plans does not meet the visitability standards required for two detached ADUs on a lot with a house. Consult with a City Planner and Building Code reviewer to discuss needed modifications.
Within the plan set, you will also need to make some decisions about construction methods. You will need to choose an energy conservation measure from the list provided in the plans. You may need to select one of the options for framing your roof if using a shed roof option.
If you choose to frame your roof using engineered trusses you will need to get an engineer-stamped truss package from a local truss manufacturer or lumber yard. You may either submit a complete truss package with these plans, or you may submit the roof framing later as a deferred submittal. If you choose a deferred submittal, construction of the ADU can begin, but roof trusses may not be installed until the trusses are submitted and approved. Deferred submittal permits incur additional permit fees.
Converting existing space to an ADU
If you plan to convert existing space to an ADU, you need to have a completed building permit application, a site plan, and architectural plans. For a complete list of submittal requirements for conversions of an existing space see “Submittal Requirements – 1 & 2 Family Residential.” You might also want to read our step-by-step guide for completing a building permit application.
Major Residential Alteration and Addition
If your project qualifies as a Major Residential Alteration and Addition (MRAA), there are additional requirements including a delay period and notification to neighbors and neighborhood associations. Review the MRAA web page for more about these requirements.
Step 3: Apply for an ADU permit online or in person
You can submit your ADU building and trades permit applications online using Development Hub PDX. Read step-by-step instructions for submitting a permit application request online or in person.
If you are using one of the pre-approved plan sets, be sure to write “Pre-Approved ADU” in project description field of your permit application.
For most projects, electronic plans are submitted through the Single PDF process.
If you need to submit paper plans, you can set up an appointment to pick up plans or drop off plans in person. You can also call us and we will work with you to schedule an appointment.
Step 4: Check plan review status and make corrections to an application
You can check the status of a permit review on in the permit search function of Portland Maps. Many permit technicians and plan reviewers might review a single permit. The Permit Review Process web page has more information about the groups that review permits.
A checksheet is sent to the applicant when a reviewer needs additional information, or a correction must be made to the plans. When you have gathered the additional information or made the corrections, you will need to send us a checksheet response with corrections. Reviewers will be notified that a checksheet response has been received and the review will continue.
Read more about:
- how to send us corrections,
- how to send corrections electronically
- how to prepare corrected paper plans
Step 5: Receive your ADU permit
You will be contacted when your permit is ready and notified of your final fee total. Instructions will be given on how to get your approved permit and pay your fees. Your permit is not issued until all fees are paid. Read more about the pre-issuance process.
Step 6: Start building an ADU and get ready for inspections
The inspection card lists all the inspections you will likely need during your ADU construction project, and what work needs to be done first.
Once your building permit is issued, erosion control measures and sometimes tree protection measures must be installed, inspected and approved prior to beginning any further ground-disturbing activities. All permits need a final approval inspection to be complete.
Step 7: Schedule an inspection, get inspection results and make corrections
To schedule an inspection, call the automated inspection request line. You will need your IVR or permit number and the three-digit code for the inspection.
Get the results of the inspection through the permit search function of Portland Maps the next day. Read more about scheduling inspections.
Contact residential inspectors about your ADU permit inspections
If you have questions before or after your inspection, you can talk with an inspector.
Other considerations
Trees: Ground disturbance or construction staging that impacts a root protection zone of an existing tree may trigger tree preservation requirements for trees located on private property and/or in the public right-of-way. The value of a project may also trigger tree planting requirements for private property and/or in the public right-of-way. More information may be found at the Urban Forestry website.
Temporary Street Use Permits: To reserve on-street parking, close sidewalks, travel or bike lanes, or to close streets to facilitate construction, contact the Temporary Street Use Permit (TSUP) Office (see “Contact Information” at the end of the ADU Code Guide) for information and requirements or apply for permits online at www.tsup.info.
Addresses: Addresses for sites with one or more ADUs will be assigned as follows:
- A single street address (number) will be assigned to the site, with letters used to designate each separate dwelling unit regardless of the orientation of the front door of the unit.
- The Unit letters (A, B, C, D, etc.) will be assigned to all dwelling units, including those on corner lots.
- The address of the ADU must be permanently affixed on the main entrance of the dwelling unit and be legible from the public way that provides access to the primary unit. When the address posted at the unit entrance is not visible from the public way, a duplicate address must be permanently affixed to a permanent structure at the entrance to the site from the primary public way.
Existing “Accessory Rental Units”: Existing Accessory Rental Units (ARUs), which were created by permit under previous zoning regulations, will be considered ADUs under the new regulations. Because of the change in some standards, these pre-existing ADUs may be nonconforming to one or more Zoning Code standards. For additional information, please contact Planning and Zoning.
Discontinuance of Accessory Dwelling Units or Accessory Rental Units: To discontinue using an existing ADU or ARU as an independent living unit, a building permit is required. The purpose of the permit is to document that the accessory unit no longer exists as a separate legal living unit.
Permanent cooking facilities in the ADU or ARU must be abandoned by removing the appliance (and exhaust hood) and permanently capping the exhaust duct serving the hood. If a gas range is being abandoned, the gas piping branch serving that appliance must be abandoned and permanently capped at the point where it originated at the trunk line. If an electric range is being abandoned, the circuit breaker(s) and receptacle serving the range must be removed, with the electrical wiring cut flush with the side of the service panel or subpanel, so that it cannot be easily reconnected. The wiring at the receptacle must be cut flush with the side of the outlet box and a blank cover plate installed.
“Illegal” Accessory Units: Property owners must obtain a building permit to legalize existing ADUs that were constructed without a building permit. Verification of the compliance of concealed building components that were covered without inspection will be at the discretion of the building inspector.