Building an ADU in Portland

Want some extra, passive income each month? Well, if you haven’t thought about building an ADU (or Accessory Dwelling Unit), you should! ADUs are extra dwellings you add on to your home or onto the same lot as your home.

They can give you more living space for you or your guests, or you can rent them out. Either way, they add a lot of flexibility to your housing situation and give you options for your housing needs in the future, too.

What Exactly is an ADU?

So, how exactly do you know if a bonus dwelling is defined as an ADU? First, ADUs are always on the same lot as the main home. They have their own kitchens, bedrooms, and bathrooms—they have all the components they need to be an entirely separate living space.

The entrance to the ADU can be either a separate outdoor entrance or an entrance from the inside of the main home.

There are a number of ways you can build an ADU. These include:

  • Adding an ADU on to your home
  • Converting an attic, garage, or basement into an ADU
  • Adding a new-construction ADU to your lot

Planning Your ADU

No matter what kind of ADU you’re building, I highly recommend going to the Development Services Center while you’re still in the planning stages of your ADU project. The people there will make sure that your ADU is allowed on your property and help you understand any relevant zoning restrictions.

You can also discuss any concerns or issues you have with your project, including structural and design elements.

Building a New Construction ADU

If you’re building an ADU from scratch, you’ll need a permit application. It’s highly likely that you’ll also need mechanical, plumbing, and electrical permits, depending on exactly what work you’re doing. The project will be reviewed under the current Oregon Residential Specialty Code, which you can see more about here. A new detached ADU needs an application for a New Family Residential Project, as well.

If you’re building a brand-new home and want to include an ADU, you’ll be doing all of the same things you (or your builder) are already doing to get the appropriate permits and inspections for the main home. Your contractor should be able to guide you through this process, which is a big advantage for building an ADU at the same time you’re already building a home.

Building an Add-On ADU or Converting Space Into an ADU

If you’re building an add-on ADU or converting space into one, the process is a little bit different from new construction. But you’ll still need plans and permits to get approval from the city to move forward.

Whether you’re converting existing space to an ADU or expanding your square footage, this handout from the city is very helpful. It tells you all about the drawings, applications, and permits you need to get approval for this project. The most important thing to remember is that you need to clearly distinguish between the home’s existing conditions and the work you’re proposing.

Zoning Regulations for ADUs

Portland allows ADUS in both commercial and residential zones. They can be added to single-family homes (including manufactured homes) and rowhouses or twin houses.

There are many rules an ADU must conform to, but here are some of the main ones:

  • The ADU can’t be more than 75% of the main dwelling’s square footage or more than 800 feet (whichever is less)
  • Detached ADUS can’t be higher than 20 feet and must sit back 40 feet from the front lot and back wall of the home
  • Detached ADUs higher than 15 feet have to match the main home’s roofs, windows, and materials
  • An ADU isn’t allowed if the main home is also used as a workplace

See more information about zoning here.

Fees for ADUs

Building permit fees are based on the work you’re planning to do. They’re unique to your project, so you’ll have to turn in all of your paperwork before you know what the fees are. There is, however, a helpful online fee estimator here.

Different city departments also require system development charges. These include Portland Parks, Environmental Services, the Water Bureau, and the Department of Transportation. Sometimes these fees can be waived under certain circumstances.

See more information about fees and charges here.

Safety Regulations for ADUs

It’s no surprise that there are all kinds of safety regulations to follow when you’re working on an ADU. There are a lot of them, but here are some of the most important.

  • Each ADU must have a shut-off valve but can use the same water supply as the main home
  • Residents need access to the electric panel and heating and cooling system
  • The ceiling height must be at least 6’ 8”

You’re sure to still have some questions, so you can find a lot more information here. Good luck with your ADU project! I think you’ll be glad you did it.

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