Learn more about Accessory Dwelling Unit (ADU) permits in the City of Portland. Get all required forms for an ADU permit. Get information about ADU inspections for basement apartments, granny flats, in-law units, mother-in-law apartments, rental units, secondary units and adding another dwelling.
An accessory dwelling unit (ADU) is a second dwelling unit created on a lot with a house, attached house, tiny house or manufactured home. The second unit is smaller than the main dwelling. You can create an ADU by:
- Converting part of the existing house
- Building an addition to an existing house
- Converting an existing garage or
- Constructing a new building
A building permit is required to convert attics, basements or garages to living or habitable space. Your project may also require electrical, plumbing or mechanical permits.
Required forms and important forms for an ADU building permit
The following information must be submitted when applying for a permit to construct an ADU. Since every project is unique, there may be some situations where you will be asked to provide additional information. Things you need to apply for this permit:
- If the project will result in disturbing the ground with mechanical equipment and
- If the project qualifies as a simple site (less than 10% slope, more than 50 feet from a wetland or waterbody and outside an environmental or greenway zone
- Erosion Control Plan
- If the project will result in disturbing the ground with mechanical equipment
- If the project qualifies as a complex site
- Can be part of the site plan
- Structural Plans & Calculations (if applicable)
- Include all existing and proposed fixtures
- Mitigation form (simplified approach form) and/or a stormwater plan if your project will add more than 500 square feet of impervious area
- If building an addition and house has a septic tank or cesspool on site
- For Combination Permits (if applicable):
- Completed (for new detached ADU only)
Step 1: Research your property and what you need for your ADU permit
Code and Rules for ADU permits
Permits are reviewed under multiple city and state codes including:
- Oregon Residential Specialty Code
- Portland City Codes
- Title 11 Tree Code
- Title 24 Building Regulations
- Title 33 Zoning Code
Other codes may apply based on the scope of work. Building Codes, Rules & Guides has links to the codes and administrative rules, code and program guides.
The program guide has an overview of zoning and construction standards. For example, zoning code has rules on the maximum size of an ADU (no more than 75% of the living area of the house or 800 square feet, whichever is less). The building code has specific rules about separation between units as well as electrical, mechanical and plumbing systems.
How to check the permit history for a 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 "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 How to Request Public Property Records webpage.
Planning and Zoning
Before getting started, contact Planning and Zoning to find out if an ADU is allowed on your property. There are also a variety of design and use standards in the zoning code which apply to the creation of an ADU. These include:
- Limits to the number of residents in both units
- Restrictions on home occupations
- Rules on the location of entrance doors
- Limits on the size of the ADU
- Design requirements for new detached ADUs (Materials
For additional requirements that apply to detached ADUs, please review:
Development Services sells a "Residential Combination" permit package. This allows you to call for all inspections using one Building Permit (RS) IVR number. You can also pay for all the permits at one time. If you choose a combination permit, you will need to submit the trade (mechanical, electrical, and/or plumbing) applications with your plans. If you are hiring subcontractors to do the trade work, they must sign their trade permit application.
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 doing the work your self, then you can sign the 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.
Decommissioning a Septic Tank or Cesspool
If you are building an addition, and the house was not connected to the sewer when it was built, you will likely need to decommission the cesspool or septic tank.
Evaluating existing space to convert to an ADU
Unfinished areas may not meet current building code requirements for living space. This includes:
- Ceiling height
- Emergency Egress Windows
- Insulation and Ventilation
These conditions could make it expensive, difficult or even impossible for you to convert into an ADU.
Excavation near property line
Be careful when digging near the property line for construction. The work should not cause damage to the next door property and buildings. The temporary excavation guidelines has information on requirements.
Major Residential Alteration and Additions (MRAA)
A major residential addition is adding more than 500 square feet of new interior space by expanding the building footprint or envelope. A major alteration means removing 50% or more of the exterior walls above the foundation. If the Major Residential Alterations and Additions have a notification rule. There is also required delay period. (Portland City Code Section 24.55.210). For more information, visit apply for a Major Residential Alteration and Addition permit (MRAA):
- Major Residential Alterations and Additions (Brochure 23)
- Major Residential Alteration and Addition Permit - Overview and Criteria
New detached ADUs
If you are building a new detached ADU, you will follow the same permit process as a new single family residence (NSFR). There are additional requirements for your permit. This does not apply to additions or conversion of existing buildings.
Permit fees for ADUs
Permit fees are based on the type of permit, the work proposed, the valuation of the work, and the staff that need to review the work. When you create a new Dwelling unit, system development charges are usually charged.
Your project must be designed to meet all structural requirements in the building code. The construction drawings must show how both gravity and lateral (wind and earthquake) loads will be resisted. Please see our page on Residential Engineering for more information on these requirements.
Step 2: What you need for an ADU permit
You will need a completed building permit application, a site plan, and architectural plans. Review the plan drawings requirements:
- Drawings, drawn to scale where necessary to verify compliance with code.
- Drawings may be handwritten/drawn if clear and legible. Text or note shall be in print.
- Minimum drawing size: 11x17. All required information is to be clear and legible. Minimum printed text is to be 3/32” or the equivalent 12-point font.
- Cannot use professional's drawings without the permission of the professional who signed the original drawings. For example, an architect’s stamped plan set cannot be used without their permission.
Depending on the scope of work, you may also need structural calculations.
If your project qualifies as a Major Residential Alteration and Addition, there are additional requirements including a delay period and notification to neighbors and neighborhood associations. See the MRAA page for more detail on these requirements.
If you are applying for a combination permit you will also need to submit the trade permit applications (Electrical, Mechanical, and Plumbing).
Each project is unique and you may be asked for additional information.
Step 3: How to submit your ADU permit application
If you are unable to create electronic plans, please call us and we will work with you.
Step 4: Plan Review process and checksheets for ADU permits
The bureaus/review groups that will check a typical conversion project include:
- Planning and Zoning
- Life Safety Review
- Structural Review
- Site Development Review
- Residential Subsurface Site Evaluation - Site Development
- Bureau of Environmental Services Review
- Portland Bureau of Transportation Review
- Water Bureau Review
- Urban Forestry Review
The related Permit Review Process webpage has more information. You can check the status of the permit review on Portland Maps permit/case search.
A checksheet is sent to the applicant when a reviewer needs additional information or a correction has to be made to the plans. When you have gathered the additional information or made the corrections, you will need to submit a checksheet response with corrections. Reviewers will be notified that a checksheet response has been received and the review will continue.
Related page Checksheet Response: Prepare corrected paper plans for submittal has information for paper plans.
Step 5: Permit Issuance for ADUs
When the last technical review is approved, your permit will be pre-issued. Pre-issuance is the last permit check. This step ensures all required reviews took place, all required approval stamps are on the plans, and the fees are charged correctly. 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.
Step 6: Start building and get ready for inspections for your ADU permit
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: Residential inspections, results and corrections for ADU permits
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 on Portland Maps permit/case search the next day.
Not approved - there are some reasons why the work did not get approved:
- no access - the inspector may not have been able to inspect the work
- incomplete work
- code violations
The inspector will list the corrections needed on the inspection report.
Call for a reinspection after making the corrections. Use the same three digit inspection code.
If you make the corrections the same day wait until 5 pm to request a reinspection. The inspector needs to enter their results before you can schedule the reinspection.
There is a reinspection fee charged for more than one reinspection for a single issue.
Contact residential inspectors about your ADU permit inspections
If you have questions before your inspection, you can talk to an inspector. The 1 & 2 family inspector area map lists the inspector's name, area, and phone number.
Because of vacation or illness, your inspector may be different than the one listed on the map. If you have questions after your inspection, find out which inspector to call. Their contact information will be on the inspection results and on Portland maps.