What exactly is an ADU?

"I have been hearing acronym ADU thrown around in conversation and have no idea what it means. So, what exactly is an ADU and why is everyone talking about it?"

Answer from Ross:

Dear Jake,

ADU stands for Accessory Dwelling Unit, but they are also commonly referred to as “mother-in-law apartments” or studio apartments. These secondary dwellings are created auxiliary to, and smaller than the main dwelling on the property. They can take form in a variety of ways, including; the conversion of a pre-existing home, new additions to an existing home or an entirely new structure. All those “tiny houses” we have been hearing about are the perfect examples of ADUs.

Thinking about creating an ADU on your property? Beware, because most jurisdictions limit the number of single-family dwelling units on a single piece of property to one. While large lots may be sub-dividable, allowing the construction of additional single-family houses, the lots are then independent of one another. In most places, the only way to add a separate building containing living quarters is to add an ADU. Typically, the ADU is limited in size by either a percentage of the main residence or a fixed number. In a jurisdiction where I recently proposed an ADU to a client, the limitation was 750 square feet. I had just enough room to design a single bathroom, kitchen and living space so while small, it is the ideal for a single resident, be it a mother-in-law, kid-back-from-college or on-site caretaker.

The limitation in size makes these units challenging but undeniably fun to design! Just take a look around at some of the wonderful designs created by clever architects, their clients and their builders. For real fun, check out the ADU tour in Portland next year, or talk to the AIA about setting up a tour in your city!

As always, make sure to do your research about zoning and property laws before delving into constructing your own ADU. For those of you in Portland, Oregon, you can check out the limitations applicable to your specific property by visiting the Development Services Center.

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