Accessory Dwelling Units (ADUs)

An Accessory Dwelling Unit, or "ADU" (also commonly referred to as an accessory apartment, mother-in-law suite, or granny flat), is a secondary dwelling unit constructed on the same property as a single-family detached house. An ADU can be within the house, attached to the house, or detached from the house. Outlined below is a summary of the development requirements for an ADU.

This ADU webpage supplements the Residential Accessory Structures webpage.

Planning

Refer to Woodburn Development Ordinance (WDO) 2.07.20 for the special use standards specific to ADUs. Applicable standards include (but are not limited to):

• The ADU shall not exceed 50% of the gross floor area of the primary dwelling or 725 square feet, whichever is less. (Garage area is excluded from the gross floor area calculation.)
• The ADU must meet the basic site development standards – including minimum setbacks, maximum lot coverage, and maximum height – for the applicable zoning district. For sites zoned Residential Single Family (RS), refer to WDO Table 2.02B.
• The architectural design of the ADU must match the design of the primary house – including finish materials, roof pitch, trim, and window proportions.
• Only one ADU is allowed per property.

Building

Homeowners will need to apply for a building permit for their ADU project. Refer to the Building Division for building permit questions.

Public Works

The ADU will need to connect to City water and sewer. Can the existing services for the house also serve the ADU or will the ADU need its own services? The development plans will need to answer this question.

System Development Charges (SDCs) are applicable for ADUs and are paid at the time of building permit issuance.

Note:  The Community Development Department has no involvement with how the Marion County Assessor would assess and tax an ADU.  For property tax questions, contact the Assessor's Office.