City of Portland, Accessory Structures Zoning Code Update

The City of Portland is in the process of streamlining and clarifying zoning standards associated with the development of garages, ADU’s and other accessory structures.

The information in this blog post is based on my review of the Accessory Structures Zoning Code Update Discussion Draft dated June 2015.  The project’s website can be found at:

The discussion draft noted three goals:

·      Standards which emphasized form over function. The height, bulk and setbacks of a structure affect compatibility greater than the use itself. Separate standards for conversion of existing detached accessory structures to ADU’s would no longer apply, since all accessory structures would be treated similarly.

·      Support the development of accessory dwellings as part of the development mix but continue to limit the overall size of the accessory structures to not overwhelm the primary dwelling.

·      Reformat the zoning code sections to improve clarity between sections and streamline locations of standards.


No changes to off-street parking requirements were made as a result of this draft. Off-street parking does not have to be provided for the accessory structure, however, existing required parking for the primary dwelling must be maintained or replaced.


1.     Detached Covered Accessory Structures. 

·      Expansion beyond garages.  New allowance would allow any small (500 sf/15 ft tall) accessory structure within the side and rear setback but would have provisions for mitigation in the form of screening and limiting windows and doors within setbacks.

·      Current building footprint is at 576 square feet and would be reduced to 500 square feet without a dimensional requirement.

·      Maximum height of 20 feet across all zones.  Current regulations can allow structures between 18 and 35 feet depending on the type of use.

·      Design compatibility for structures over 15 feet in height.

·      Building coverage limited to 15% for all accessory structures.

·      Location requirement reduced from 60 feet from the front lot line of 6 feet behind the dwelling to 40 feet or directly behind the house.

·      No change to the requirement about size: ADU’s can be no more than 75% of the primary dwelling’s area or 800 square feet. NOTE: The report noted that staff considered allowing basement conversions at greater than 800 square feet if under the 75% area, but this issue has been moved to the Single-dwelling residential infill development project.

2.     Detached Uncovered Vertical Structures. These are things like trellises, arbors, flagpoles and other vertical elements.

·      Current regulations allowing a 3 by 3 ft. and up to 8 feet high in all setbacks are maintained and allows for greater size within the setbacks if they meet the regulations associated with the accessory dwelling.

·      Current regulations for flagpoles or arbors within the front setback are maintained.

3.     Detached Uncovered Horizontal Structures. Minor modification to the code to clarify between an attached building extension, like a deck and those elements detached from the house.

4.     Mechanical Equipment. Changes to the code would allow for detached mechanical equipment in the side and rear setback if they are no more than 5 feet tall and meet City standards for noise. Provisions for wall-mounted mechanicals are also proposed.

The proposed changes would modify code sections in the following Chapters: Chapter 33.110, Single-dwelling zones; Chapter 33.120, Multi-dwelling zones; Chapter 33.130, Commercial zones; Chapter 33.140, Employment and Industrial zones. The City’s commercial zones outside of the Central City are currently under review as part of the Mixed use Zones Project, which is not quite at the code development stage. Changes are also proposed to Chapter 33.205, Accessory Dwelling Units and minor changes to Chapter 33.910 Definitions and Chapter 33.930, Measurements.

There is still time to weigh in with your concerns and approvals on these changes as presented in the Discussion Draft. Comments can be made directly to Bureau of Planning and Sustainability staff until July 24th at 5PM.  For more information about how to comment, visit the project’s website:

After July 24th, the project’s website notes that City staff will incorporate comments received on the Discussion Draft into a Proposed Draft to the Planning and Sustainability Commission who will hold a public hearing, expected in September  2015. At the hearing, the Planning and Sustainability Commission will consider public testimony and then forward a recommendation to City Council for consideration and additional public review before final adoption.

For questions about how these changes may specifically affect your project or strategies for consideration, contact UrbanLens Planning, LLC.