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.
Under Oregon's tax laws, the construction of an ADU could significantly increase the property taxes. That's because the amount of taxes levied each year and how they are determined is part of Oregon's complicated and complex law. It takes into consideration the effects of Measures 5 and 50, and those make it difficult to predict just how much taxes will increase or decrease if you build an ADU.
So before you start an ADU project, it's important to contact the assessor's Customer Service line at 503.988.3326.