The city of Portland has many types of ADU’s that are allowed.  Here is a list of the most common types that are permmited. 

Detached ADUs:

These are standalone structures separate from the primary residence, often found in the backyard of a property. Detached ADUs offer privacy and independence, making them ideal for homeowners looking to create additional rental income, accommodate extended family members, or establish a home office away from the main house.

    • Advantages: Detached ADUs can offer complete privacy and autonomy for both the homeowner and the occupants of the unit. They can be designed in various styles and sizes, providing flexibility in accommodating different needs.
    • Disadvantages: Building a detached ADU can be more costly and require additional space on the property.  Also, building a 1 story detached ADU is going to take up quite a bit of your backyard space.
Types of ADUs allowed in Portland

Attached ADUs

These are attached to, or integrated into the primary residence. They can also be attached through a breezeway or garage. These units are commonly converted portions of the main house or additions to the main house. Attached ADUs are convenient for homeowners seeking to keep the overall building footprints smaller while still enjoying the benefits of rental income or multigenerational living.

    • Advantages: Attached ADUs are typically used when trying to maximize the building lot, or when setbacks prohibit building a detatched structure.  Can be less expensive than a detached ADU when it comes to installing utilities.
    • Disadvantages: Privacy could be a concern with attached ADUs, as occupants may feel less secluded from the main house.
Attached ADU Portland Oregon

ADU above Garage Conversion:

    • Advantages: Building an ADU above an existing garage can keep your building lot footprint low while maximizing your size for an ADU.  Opportunities for decks or other unique spaces are available with this option.
    • Disadvantages:  Even if you’re able to use the existing foundation from the garage, this is the most expensive ADU option by far.  You’ll need to retrofit the existing garage, and account for a longer build time.
Garage Conversion ADU Portland Oregon

Basement ADUs:

    • Advantages: Basement ADUs make use of underutilized space and can provide a significant amount of living area without altering the exterior of the home. They often offer natural insulation, making them energy-efficient.  This is can be the least expensive option when it comes to ADU’s
    • Disadvantages: Basement ADUs may require significant renovations, including waterproofing and addressing issues related to moisture and ventilation. Limited natural light can also be a drawback unless proper design considerations are made.
Basement ADUs Portland Oregon

Two-Story ADU:

  • Advantages:  Two-story ADUs typically offer more square footage compared to single-story units, increased privacy and functionality, flexible layout options, and can retain some of the outdoor space .
  • Disadvantages of a Two-Story ADU: Building a two-story ADU may be more expensive than a single-story unit.  They have access challenges for people with mobility issues, and generally require more maintenance and upkeep.
2 story ADU Portland Oregon

Single Story Garage Conversion ADU:

  • Advantages:  Utilizes an existing structure, minimizing the need for new construction.  Single story garage conversion ADUs are typically one of the more affordable ADU options.
  • Disadvantages of a single story ADU: Loss of parking and storage space.  Size and design of ADU is affected by the size and shape of the garage.
Garage conversion ADU Portland Oregon

Also, as of 2022 Portland is allowing 2 ADU’s per property.  Ultimately, the best choice for an ADU depends on factors such as budget, space availability, zoning regulations, and personal preferences. Each option offers its own set of trade-offs, so it’s good to carefully consider these factors before making a decision.