ADUs are one of the most popular residential structures in the Portland Metro area these days, but what are they exactly? To find out, we reached out to Propel Studio, an architectural firm that works with many clients to design their perfect ADU.  We sat down with Nick Mira, one of the partners at Propel Studio, to discuss all things ADUs. 

What is an ADU? 

ADU is defined as an accessory dwelling unit – a second smaller residential structure on a property that exists in addition to the primary residence.  An accessory dwelling unit as defined by the City of Portland as a space made livable by having an area to bathe and cook. Other names for this project type include granny flat, backyard home, backyard cottage, mother-in-law suite, and many others. 

What are the benefits of an ADU? 

There are many community and individual benefits in having an ADU.  Looking at ADUs through a community lens, it allows increased density within the City boundaries without creating new land (by expanding the urban growth boundary) or new infrastructure like roads and utilities. Property owners are utilizing the infrastructure already in place and creating new places for people to live. In addition, it limits the sprawl that naturally happens within Cities as the population increases. It allows for diverse housing types like barrier free living, multi-generational living, and often are designed for aging-in-place or barrier-free housing. Finally, it allows the City to address the affordable housing crisis by increasing available housing units.  

Benefits for an individual homeowner include a possible rental income source.  Since ADUs are self-sufficient, many property owners rent them out to generate additional income.  ADUs may also allow multigenerational housing within your property boundaries by designing a space for an elderly family member that gives them the accessibility and mobility they need. Lastly, as homeowners plan to age in place, some have designed their ADU to downsize their living and rent their larger primary residence to generate increased income as retirement looms. 

ADU’s are built to the current energy efficiency and earthquake code and provide for a quieter and safer alternative to an older home. This is a common reason people ask us to design a great new place for them to move into, while they rent out the main house. 

Where are ADU’s allowed? 

Within the city of Portland, ADUs are allowed on any property with an existing single family house. There is an ADU code within the city’s planning and zoning codes that outline the regulations and restrictions. They are generally positioned in the rear of the property as detached structures, but may also be attached to the main house, located in a renovated basement, or be carved out of the main living space of the house. By far, the easiest, most convenient and most common option is to do a fully detached ADU in the backyard. 

Portland Accessory Dwelling Unit ADU (Photo Credit: Josh Partee)

What size ADU is allowed? 

The City of Portland allows an ADU to be up to 800 net square feet or 75% of the size of the main house, whichever is smaller.  The area is measured from the interior surfaces of the exterior walls while garages, and attic spaces within the ADU do not contribute to the net square footage. 

Do I need to provide additional parking for a new ADU? 

Under current code, this depends where the house is positioned to public transportation. The primary residence must be within 500 feet from a frequent bus line or 1,000 feet from a MAX station. If the primary residence isn’t well served by public transit, a parking space may be required. However, if the proposed Residential Infill Project gets adopted, no parking will be required.

May I sell or rent my ADU? 

You are allowed to rent your ADU and you may also be able to sell your ADU, although that becomes a bit more complicated. It is possible to create a condominium on your property and sell the ADU separate of the primary home. However, most ADUs are used as rentals, as long-term housing for aging family, or for downsizing while renting out the main house. 

May I convert an existing accessory structure into an ADU? 

This could be possible. The conversion will trigger a review of current code requirements and it will require compliance with seismic, and life and safety upgrades.  Having an architect on board will help you do that feasibility study of an existing structure and help you determine your best course of action. In general, we usually don’t recommend renovations to older accessory structures as they weren’t designed and built to live in, and often take more work and cost more than simply building a new structure. 

What about utility connections? 

This will be location dependent, but typically we tie into the existing water and sewer lines of the existing house while bringing in new electrical service for the ADU.  A new water service within the City of Portland is allowed, but will cost north of $6,000 and other SDC fees will apply as well. A visit to your local municipality or county will help you determine what the exact requirements and costs are. 

When do you need to involve an architect? 

It is advantageous to involve an architect as soon as possible.  An architect builds value and makes your ADU conform to your specific lot requirements and City code.  Architects will take the time to listen and learn what is unique to your needs and design style and then create a space that complements your lifestyle. Architects then consider your ideas, taste and budget, and balance that with the codes, regulations, and technical aspects of building a new structure to create a design that addresses all of these forces. We usually recommending reaching out to an architect as early in the process as possible as they will be great resources as you consider your options and they can help visualize your ideas as you work through the design. 

ADU Design (Credit: Propel Studio)

Where can you find more information about ADUs?

If you are looking for more information about ADUs, the design process, cost of construction, or want to see some examples of ADU project check out the Propel Studio website – www.propelstudio.com. Propel has designed over 50 ADUs to date, and are one of the leading experts in this project type in the Portland area. They also offer consultations to those who are ready to start the design process (https://calendly.com/propelstudio/60min).

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