Accessory Dwelling Units

An Accessory Dwelling Unit, or "ADU" (also commonly referred to as "mother-in-law unit"), is a small secondary dwelling unit constructed on the same property as an existing primary dwelling unit.  ADUs are permitted outright on most residential properties, subject to the development standards of Corvallis Land Development Code (LDC) Section 4.9.40. 

An ADU complying with the standards of LDC Section 4.9.40 can be developed through the building permit process.  Applicable LDC standards include (but are not limited to):

• The ADU shall not exceed 900 sq. ft. of floor area, or 85 percent of the primary dwelling's floor area, whichever is less.
   
• The ADU must meet the height, lot coverage, and Green Area standards of the underlying zone as applicable to the primary dwelling unit, except that there is no Private Outdoor Space requirement for an ADU.
   
• The ADU must meet the setback standards of the underlying zone as applicable to the primary dwelling, with exception that ADUs are not subject to maximum front yard setbacks.  (Special setback requirements apply to detached ADUs located on Townhouse lots; please review LDC Section 4.9.40.e for more information.)
   
• Only one ADU is allowed per property.

In addition to LDC standards, an ADU must include sleeping, kitchen, and bathroom facilities, and must comply with building code (ORSC) and City Municipal Code requirements for a single-family dwelling.  This includes the requirement to connect to water and sewer services.  Typically, ADUs are tied into the property's existing water and sewer services. 

An ADU may be either integrated into the same building as the primary dwelling, or constructed as a separate freestanding dwelling.  If integrated into the same building as the primary dwelling, fire separation walls / ceilings are required between the two units.  If constructed as a separate freestanding dwelling, building code generally requires a minimum separation of 6 feet between the units.

If you would like to know whether an ADU would be permitted on your property, or have other ADU-related questions, please contact Development Services at 541-766-6929.