What Is an ADU?

ADUs are “Accessory Dwelling Units.” You’ve also heard ADU’s called minihouses, tinyhouses, mother-in-law apartments, Ohana suites, granny flats, and several other terms. 

According to the American Planning Association, “An accessory dwelling unit (ADU) is a smaller, independent residential dwelling unit located on the same lot as a stand-alone (i.e., detached) single-family home.”

In Portland, an ADU’s square footage must be less than 75% of the square footage of the main house on the property or 800 square feet – whichever is lower. Let’s say your property’s main house is 1,000 square feet. If you wanted to build an ADU on that property, it couldn’t be more than 750 square feet.

ADU’s also cannot legally exceed 18 feet high. 

Are there different kinds of ADU’s? 

There are countless ways of building ADU’s- you can use empty space you currently have, such as an attic, basement, or garage, or you can construct a whole new structure on the property. Broadly speaking, there are two “types” of ADU’s, owing to the differences in rules and regulations they each have to follow. 

Attached- These are dwellings added to or using the existing main structure of the current home on a lot. This might mean converting an attached garage, attic, basement, or internal apartment.

Since you’re not starting all the way from scratch here, construction costs are typically far lower for attached ADU’s, and depending on the space, you might need less (or more) involvement with “the City.”

Detached (DADU)- This involves the building of a whole new, separate dwelling unit on the lot of an existing home, from the foundation up. With all that new construction work, these tend to be more expensive, and they also involve different processes across the board: from different planning and design procedures to permitting and licensing with the city of Portland.

Why do people get ADUs?

Folks tend to be interested in ADUs for the investment or the lifestyle.  

Get you a little house that can do both! 

The ADU Lifestyle 

Do you want to live in a small house? Does your family member want to live in a small house on your property? Owing to their small size, ADU’s are both ethically and functionally versatile – no matter what you put into your ADU or how you use it.

The ADU as an Investment

Even if you don’t plan on occupying it, building an ADU on your current property a great financial investment. 

• Increase your property value 
• Make an income by renting to tenants 
• ADU tourism

Note: if you’re thinking about getting a tiny house as an investment, remember that you’re literally building a home (to be inhabited by a human being- who may have different abilities or resources than you). 

No matter what, if you’re going to invest in an ADU, think about your city and how the addition of your home might impact your community.

Know before you build

Just because you’ve thoughtfully considered your personal balance of investment and/or lifestyle doesn’t mean you can just start building when you feel like it.

The rules that govern ADU building are different from state to state, and municipality to municipality, so be sure to check in with your local development services for location-specific procedures. 

In Portland, whether you’re building an ADU to live in or rent out, you’ll have to follow the same process. Here are a few things you’ll need to know before you get started:

There are rules! 

ADU’s are legally defined as dwellings, and as such they need to satisfy a number of building and zoning codes that any other housing unit would need to pass. 

Before you can build one you need to…

• Apply for, pay, and obtain the proper permits and applications
• Building plans and drawings need to be approved by the city
• Property needs to pass inspections 

Not sure what permits you need? The City of Portland has an excellent tool that will help you figure out what to apply for and the costs of permitting fees in your area.

For more information about ADU rules, regulations and requirements in Portland, Oregon, visit the latest version of the City of Portland’s ADU Program Guide 

There’s a process

• Research and brainstorming
• Planning
• Design
• Hiring contractors
• Permitting and applications
• Inspections
• Inhabitation

There are finances to think about 

Check out this blog post that explains the financing piece in a bit more detail. It’ll help you get started thinking about price tags and funding for your project. 

For now,

• What is your budget for your ADU?
• How much do you have saved for a upfront costs like down payments, closing costs, and designers? 
• Do you have any equity built up in your home?