Support Us Button Widget

ADU 101: How to add a small, secondary home to your Portland backyard

Additional dwellings can be built as standalone structures, carved out within an existing home, or converted from a garage.

A small, standalone dwelling painted sage green with a dark orange door and multiple windows, is surrounded by a lawn and a wooden fence.

In Portland, two ADUs are allowed on sites with a house, attached house, or manufactured home.

Photo via the city of Portland

Table of Contents

We don’t have to tell you that Portland is in need of more affordable housing options. While local leaders work to fulfill the Metro Affordable Housing Bond and developers pitch plans for new construction, local homeowners can consider their own option: building an accessory dwelling unit, or ADU.

What qualifies as an ADU?

Also known as an in-law unit, granny flats, or backyard cottages, the city of Portland defines an ADU as “an additional dwelling unit created on a lot with a house, attached house, tiny house, duplex, or manufactured home.” An ADU is smaller than the main home and can be created by converting part of the existing house or garage, or by constructing a new building. Fun fact: a floating home cannot have an ADU.

Can I build one on my property?

Before you start loading up on lumber, you’ll want to research your home’s permit history and make sure your ADU dreams align with the city’s zoning codes. The Bureau of Development Services has a handy worksheet to help with the process.

Once you’re in the clear, you can start shopping for contractors — or learn what the state of Oregon requires if you plan to do the work yourself.

How much will it cost me?

Living Room Realty estimates that building a new, detached ADU from scratch costs at least $200,000-$250,000. You can explore different financing options, like taking out a home equity loan, through local institutions specializing in ADU builds.

Keep in mind that adding an ADU will lead to increased property taxes.

Where can I learn more?

Read more about Portland’s ADU building requirements, or schedule a free 15-minute appointment to talk with an expert (such as a city planner or permit technician) online or over the phone.

More from PDXtoday