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Development Services

From Concept to Construction

Phone: 503-823-7300

TTY : 503-823-6868

1900 SW 4th Ave, Portland, OR 97201

Accessory Dwelling Units (ADUs)

You will find information on this page about adding an accessory dwelling unit to a property. Every dwelling unit functions as a separate unit. They are commonly known as "mother-in-law apartments", "granny-flats" or studio apartments.


Getting Started

An accessory dwelling unit (ADU) is a second dwelling unit created on a lot with a house, attached house or manufactured home. The second unit is created auxiliary to, and is smaller than, the main dwelling. ADUs can be created in a variety of ways, including conversion of a portion of an existing house, addition to an existing house, conversion of an existing garage or the construction of an entirely new building. 

Methods to create an ADU

  • Chapter 33.205 of the City of Portland Zoning Code provides the standards for accessory dwelling units in all Residential (R) zones. ADUs can be created in a house (detached single family dwelling), an attached house or a manufactured home any of the following ways:

    a. Converting existing living area
    b. Finishing an existing basement or attic
    c. Building a new structure
    d. Making an addition to an existing structure

    Where attached housing was created under the infill provisions of the ‘a’ overlay zone (section 33.405.060), or as duplexes and attached houses on corners (section 33.110.240 E), ADUs are prohibited. Attics and basements with limited ceiling heights may not qualify as space that can be converted.
     
  • Some existing attached or detached garages can be converted into an ADU in all R zones. ADUs can also be created by construction of a new accessory structure.

Visit the Planning and Zoning staff at the Development Services Center to determine the specific limits applicable to your property.

A building permit is required to build an accessory dwelling unit. Depending on the scope of work, your project will most likely also require electrical, plumbing and/or mechanical permits. 

For new construction, your permit will be reviewed under provisions of  the  current Oregon Residential Specialty Code. View more information on building codes.

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