Portland standards for “accessory dwelling units” (ADUs)

Here are some of the applicable standards:

1. Maximum Size.

800 square feet and no more than 75% of the total living area of the existing house.

2. “Attached” or “Detached”.

• Attached: ADU and house must abut opposite sides of the same wall.
• Detached: ADU must be at least 60′ from street and 6′ behind house.

3. Maximum Height for Detached SDUs.

18 feet.

4. Lot coverage for Detached SDUs.

• Cannot exceed the lot coverage of the existing house
• Combined coverage of all accessory structures cannot exceed 15% of the lot.

5. Design Review

• Exterior finish materials, roof pitch, trim, eaves, window orientation and dimension must be the same or visually match those of the house.
• Design review is required for development of ADUs in Portland’s ‘d’ overlay zone, when external modifications to the site or existing house are made. These ADUs must meet the Community Design Standards, where allowed, or, alternatively, be approved through the design review process.

6. Maximum Occupants.

Portland limits the total number of occupants on a “single-family” lot to the total allowed for a single household. This is an especially important limit that prevents overloading established single-family neighborhoods.

For more information, visit Portland’s ADU web page.