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You will find information on this page about adding an accessory dwelling unit to a property, or converting a structure to a duplex. Every dwelling unit functions as a separate unit. They are commonly known as "mother-in-law apartments", "granny-flats" or studio apartments.
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
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 may also require electrical, plumbing and/or mechanical permits.
Your permit will be reviewed under provisions in the Residential Specialty Code (Formerly the One and Two Family Dwelling Specialty Code) based on the 2003 IRC. View more information on building codes.
|Prior to applying for a permit to create an ADU within an existing house, the applicant must request an inspection of the existing structure. The inspector will complete an inspection report noting any necessary corrections.
A pre-application inspection is not required where the ADU is being created as part of a new building, by an addition to a house or in an accessory building.
|The following information must be submitted when applying for a permit to build an ADU. Since every project is unique, there may be some situations where you will be asked to provide additional information.
|Site Plan (Scale site plans to most appropriate scale, e.g. 1”=10’ or 1/4”=1’)|
|Architectural Plans (Scale of plans to be ¼”=1’ and details scaled to ½”=1’. Single line drawings are not acceptable – plans must be drawn to show wall thickness)|
|Structural Plans (Scale of plans to be ¼”=1’, details to be ½”=1’)|
If you are hiring sub-contractors to do work on your project, and know who they are when applying, they will be listed on your permit at that time. If you don't know when you apply for your permit, they can be added after issuance. Sub contractors you hire must be registered with the State of Oregon and carry a current CCB license.
|Things to consider:|
|(1) Converting to a Duplex|
|In unfinished areas, existing features such as ceiling heights, windows, stairs and insulation may not meet current building code requirements for finished space. These conditions could make it expensive, difficult or even impossible for you to change your attic, basement or garage into living space.
|(2) Design Standards|
There are a variety of design and use standards which apply to the creation of an ADU. These include limiting the overall number of residents in both units, limitation with respect to home occupations, the location of entrance doors and size of the ADU. Where an ADU is created in a new or existing detached structure or by the addition to a house, there are additional standards regulating the exterior appearance and materials of the ADU. These additional standards include provisions for the height, roof pitch, trim, eaves and windows.
|(3) Construction Standards|
|The ADU Program Guide outlines the construction standards for ADUs.|
|Regulations require that each separate structure have a separate water service. For more information call the Bureau of Water Works at (503) 823-7368|
|(5) Sanitary and Storm Sewers|
|The ADU can either connect to the existing sanitary sewer system or have a separate connection. If a separate connection is made, a sanitation permit is needed for the installation.|
|(6) Decommissioning a Septic Tank or Cesspool|
|When building an ADU, the septic tank/cesspool must be located (if one exists).|
|(7) If any ground disturbance, erosion control review and inspection may be required.|
The yellow inspection card lists all the inspections you will likely need during your construction project, and what work needs to be done first.
Once your building permit is issued, erosion control measures must be installed, prior to beginning any further ground disturbing activities.