An ADU is a dwelling built on a lot that already has a house, attached house, duplex, or manufactured home. The ADU must be smaller than the main dwelling. You can create an ADU by:
- Converting part of the existing house
- Converting an existing garage or accessory structure
- Constructing a new building
You'll need building and trade (electrical, mechanical, and plumbing) permits for this project
We require a building permit if you want to convert an attic, basement, or garage to a living or habitable space. You'll also need a building permit to build a new ADU.
For convenience, the City of Portland offers pre-approved building plans for detached ADUs. If you want to build one of these, you should submit those plans with your building permit application. See Step 2 below for more information about pre-approved plans.
Your ADU project will also need trade (electrical, plumbing, and mechanical) permits. You can apply for trade permits at the same time as your building permit, or you can do that later. The advantage of applying for both kinds of permits at the same time is that you'll have one permit number. But you can apply and pay for trade permits 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. If the value of your home increases, your property taxes will too. The county assessor, not the City of Portland, determines your property taxes.
Before starting your project, contact your county assessor. They can help you learn how your taxes may change.
Evaluate existing space for ADU conversion
Constructing an ADU within your existing home may be an option. But you should be aware that some areas in your home might not meet requirements for a living space.
Common issues can include:
- Ceiling height
- Emergency exit windows (also known as "egress windows")
- Insulation and ventilation
- Stairs
These issues could make it expensive, difficult, or even impossible for you to convert a space into an ADU. Use the information in Step 1 below to start researching your property.
Step 1: Research your property before you build an ADU
Check the permit history for your house
It's important that you verify the permit history of your property. If there's been construction that didn't have a permit, you'll need to get a permit for that work as if it were a new project.
Depending on the age of your house, we may have plans that show its permit history. Visit our public records web page to request permit records for your home. You should verify work with actual permits, and not rely on tax information from the county.
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:
- Requirements for short-term rentals
- 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 to property lines. It will also tell you how many structures you can build on a lot. This worksheet describes the zoning rules for detached accessory structures like ADUs.
Learn how to research the zoning of your property.
Learn more details on zoning code standards, such as visibility and height allowances.
Learn about required city utility connections
Your ADU might share water systems with the main dwelling, or it might have its own connections. This depends on factors like the number of fixtures you'll have in the ADU and if there's a septic tank involved.
Get more information on water and sewer requirements here.
Research Flood Hazard and Slope Hazard Areas
Your project might have special restrictions if it's in a flood, slope, or landslide area. For example, you might not be able to convert a garage that's located in a flood hazard area.
Figure out if your property is in one of these areas by searching the address on PortlandMaps.com. The information is in the Public Safety tab, in the Hazard section.
If your project site has a slope of 20% or more, or if it's within a landslide area, it will need a soils report. This is also known as a "geotechnical engineering report." If your property is within a floodplain, learn more about preparing here.
You can get a soils report and more information from the City. Schedule a free 15-minute appointment with a Building Code and Engineering Reviewer.
Learn about construction standards
Different types of projects will have different construction standards. These standards help your new structure stay safe and durable for the people who will live in it. Below are the codes that each type of project must follow:
- New, detached ADU - Oregon Residential Specialty Code
- ADU addition to single-family dwellings - Oregon Residential Specialty Code
- ADU conversions - Accessory Dwelling Unit Code Guide
- ADU addition to a townhouse - Townhouse Code Guide
ADU conversion within a townhouse - Townhouse Code Guide
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 needs to list the contractor's CCB number before we can issue the permit.
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 SDCs 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 (SDCs)
New and conversion ADUs can sometimes lead to System Development Charges. These are charges that help offset the impact a new project has on City systems, like roads and sewers. SDCs can add significant cost to your ADU project.
Find out more information about SDCs.
ADU SDC waiver program
The City can waive SDCs for ADUs if you promise not to use the ADU as short-term rental for a period of 10 years. This promise is called a covenant. A short-term rental is a property that can be rented on less than a month-to-month basis.
You may be eligible to apply for an SDC waiver. Learn more about this program.
Use this form to start the SDC process or ask for an exemption.
Transportation SDCs
For ADUs where SDCs are not waived, the Bureau of Transportation charges an SDC. See the fee schedule for Transportation SDCs.
Environmental Services SDCs
For ADUs where SDCs are not waived, the Bureau of Environmental Services charges an SDC. The amount of the SDC is based on any fees already paid and the current sewer connection charge.
In some cases, you'll need to change how your ADU connects to the sewer and wastewater systems. You might need to increase the size of the line, or put in a separate connection. If this happens, there will be more fees, even if we waive the SDC.
See the fee schedule for Environmental SDCs.
Parks and Recreation SDCs
For ADUs where SDCs are not waived, Portland Parks and Recreation charges an SDC for the creation of any ADU. See the fee schedule for Parks and Recreation SDCs.
Water Bureau SDCs
The Water Bureau doesn't automatically charge an SDC when you build an ADU. If the ADU doesn't need a change to the size of the existing water meter, then there's no charge. Find out more information about water connections.
Upon request, the Water Bureau can verify your existing water service size. If you need an increase, there will be a charge for increasing it, along with a bigger water bill in the future.
Contact the Water Bureau for more information.
Step 1b: Still need help? Schedule a 15-minute appointment
This is an optional step. Experts from the following review groups can help you get started. You can schedule a free 15-minute appointment with any of these reviewers:
- Meet with a City Planner to get information about Zoning and Tree Code requirements.
- Meet with a Building Code and Engineering Reviewer about building code, engineering, and developing a site.
- Meet with a Permit Technician if you need help with the permit or application process.
- Meet with a Water expert to see if your project requires you to increase the size of your existing water meter.
- Meet with a Sewer and Stormwater expert to find out if you need to upgrade to your sewer service.
- Meet with a Fire expert for questions about general fire safety during development
- Meet with a Transportation expert to see if your project involves right-of-way improvements.
- Meet with an Urban Forestry Tree Technician for questions about trees and tree permits.
Step 2: Prepare an ADU building permit application and required forms and documents
All ADU construction projects need 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. They're pre-approved to meet building code requirements. The City of Eugene provided these plans to the City of Portland, with minor changes, at no cost.
You're not required to use or submit these plans, but they're free and can speed up the permitting process. They're not suitable for all lots.
There are four pre-approved design options to choose from that vary in roof and foundation type:
- Note: This design will exceed size limits for a rear or side setback.
If your ADU will be on a rear or side setback, adding a cover over the concrete landing will exceed the size limit. 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 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'll 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.
A roof might be framed with rafters or engineered trusses. If you frame your roof with engineered trusses, you'll need to get an engineer to stamp the truss package. You can get one of these from a local truss manufacturer or lumber yard. You can submit a complete truss package with these plans, or you can submit it later as a deferred submittal. If you do a deferred submittal, you can start building, but you can't install the roof trusses until we issue it.
Converting existing space to an ADU
If you plan to convert existing space to an ADU, you'll need the following materials:
- Completed building permit application
- Site plan
- Architectural plans
- Structural plans (if you're proposing structural changes)
For each item, there's more information you'll need to give us. This is just an overview. For all the requirements, see Submittal Requirements – 1 & 2 Family Residential. You should also read our step-by-step guide for completing a building permit application.
Major Residential Alteration and Addition
If your project is large or involves a big change to an existing structure, you might need to notify your neighbors. Check to see if your project is a Major Residential Alteration and Addition (MRAA). Review the MRAA web page for more about these requirements.
Step 3: Apply for an ADU permit online or in person
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 pre-approved plans, make a note of it on the permit application. Write “Pre-Approved ADU” in the project description section.
For most projects, submit electronic plans 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 in the permit search function of Portland Maps. Multiple permit technicians and plan reviewers will review your permit. The Permit Review Process page has more information about who reviews permits.
If a reviewer sees an issue with your plans or needs more information, they'll send you a checksheet. A checksheet is a list of corrections you'll need to make. After you get the requested information or make corrections, you'll send a response. Reviewers will get a notification that you responded, and the review can continue.
Read more about preparing and sending checksheet corrections.
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'll likely need during construction. This will help you determine what work to do first.
Some construction might disturb the ground or trees. If that's true for your project, you'll need to install erosion control and tree protection at the site. We need to inspect and approve those protections before you continue work.
All permits need a final approval inspection to be complete.
Step 7: Schedule an inspection and get inspection results
There are two ways to schedule an inspection. You will need your interactive voice response (IVR) or permit number.
- Access Development Hub PDX, sign in, and click Inspections. Scheduling and complete results are available online.
- Call the automated inspection request line at 503-823-7000.
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
If the property has trees with trunks larger than 12 inches, you need to take protective measures. The value of a project might also require you to plant trees. You can find more information at the Urban Forestry Website.
Temporary Street Use Permits
Some construction projects will need to make use of public streets and sidewalks. Contact the Temporary Street Use Permit Office if you need any of these for your project:
- Reserved on-street parking
- Closed travel or bike lanes
- Closed sidewalks
- Closed streets
Addresses
Addresses for sites with one or more ADUs will be assigned as follows:
- A single street number is assigned to the site. Letters will designate each separate dwelling, no matter where the front door is.
- We will assign unit letters (A, B, C, etc.) 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. The numbers and letters must be legible from the public way that provides access to the primary unit.
- If the ADU entrance isn't visible from there, you must permanently affix the address to a permanent structure at the entrance from a public way.
Existing “Accessory Rental Units”
Earlier zoning regulations included permits for Accessory Rental Units (ARUs). We consider these to be ADUs under our current zoning regulations. Because regulations have changed, ADUs that used to be ARUs might be out of compliance. Contact a city planner for questions about ARUs.
Discontinuance of ADUs or ARUs
To stop using an ADU or ARU as an independent living unit, you'll need a building permit. The purpose of the permit is to document that the unit no longer exists as a separate legal living unit.
To discontinue the unit, you must remove all cooking facilities. This involves removing the appliance, exhaust hood, and permanently capping the exhaust duct.
Certain fixtures need to be "abandoned." This means deactivating the utility and making it unusable. For gas ranges, you must permanently cap the range's pipe where it originates from the trunk line. For electric ranges, you must cut the range's wiring flush with the side of the service panel or sub-panel. Then, install a blank cover plate.
“Illegal” accessory units
Property owners need to get a permit for ADUs that were built without permits. It's up to the building inspector to verify any elements that are hidden by the finished ADU. Verification might involve demolishing or removing elements of the structure. This is to verify that the work was performed correctly and safely.