Portland City Council Approves Accessory Dwelling Unit (ADU) Zoning Code Updates

Small Accessory Dwelling Units (ADUs) are now allowed in setbacks
Small Accessory Dwelling Units (ADUs) are now allowed in setbacks

After recommendations from an exploratory committee and feedback from stakeholders, the Portland City Council voted 4-1 to approve the new Accessory Structure zoning code. This has created a single set of rules that regulates all accessory structures, from ADUs to Garages. If you have been wanting to build creative Accessory Dwelling Unit, the new rules will be a welcome development by loosening the design restrictions. Further, they incentivize building small which leads to more sustainable and affordable housing.The biggest change is that they now have two sets of rules. One that regulates small ADUs under 500 square feet, and a separate one for larger ADUs, 500-800 square feet. Below is a list of the updated rules that will have biggest impact for each project type and some personal thoughts on each.

Small ADU’s - Less than 500sf, less than 15 feet tall  
  • - No design limitations - Windows can be any proportion - exterior material palette is not limited to what exists on the main house - can be built in the property setback - roof can be any slope

These are the biggest changes and the ones we are most excited about. Basically what the city is saying, is that if your ADU is a small structure you are free to make it any style you want. This makes sense as smaller, lower structures have less of a visual impact on your neighbors and from the street. We still wonder why the ADU zoning code regulated style at all. We can’t wait to work with clients who want to explore the new design options this allows.

The loosening of the design restrictions is particularly good for people looking for a more modern or contemporary aesthetic. Most of Portland’s housing is more historical in aesthetics yet lifestyles and taste have dramatically changed. Especially with small living units like an ADU, connection to the outdoors is vital to make the space feel larger and spacious. In our relatively moderate climate making use of outdoor rooms as part of the living area makes sense. Many of our clients have asked for glass walls, large windows and a modern aesthetic and until now the city code limited what they could do by forcing them to match the style of the main house. Fortunately this silly regulation has been removed for the smaller ADUs.

Another huge advantage to the new rules is the increased flexibility of locating the project on a site due to the ability to now build within the property setbacks. For smaller properties or situations where you are trying to maximize usable yard or avoid significant trees, this opens up the ability to make full use of your property. It also gives additional flexibility in siting an ADU to optimize its orientation for solar panels, natural lighting, and other sustainable strategies.  

Large ADU’s - over 500 sf

Unlike the smaller ADUs, not as much has changed for the regulations of larger ADUs. The main change is that the previous height limit of 18 feet has been increased to 20 feet.  This is particularly good for those considering a 2 story ADU or dwelling over a garage. There were also some small tweaks to the design constraints, that we think are a small step in the right direction - giving increased options for designers and owners.

  • EXTERIOR FINISH MATERIALS:The exterior finish materials on the detached covered accessory structure must meet one of the following:
  • - The exterior finish material must be the same or visually match in type, size and placement, the exterior finish material of the primary structure; or
  • - Siding must be made from wood, composite boards, vinyl or aluminum products, and the siding must be composed in a shingle pattern, or in a horizontal clapboard or shiplap pattern. The boards in the pattern must be 6 inches or less in width.
  • ROOF PITCH: The roof pitch of the detached covered accessory structure must meet one of the following:
  • - The predominant roof pitch must be the same as the predominant roof pitch of the primary structure; or
  • - The roof pitch must be at least 6/12.
  • TRIM: The trim on the detached covered accessory structure must meet one of the following:
  • - The trim must be the same in type, size, and location as the trim used on the primary structure; or
  • - The trim around all windows and doors must be at least 3 ½ inches wide.
  • WINDOWS: The windows on all street facing facades of the detached covered accessory structure must meet one of the following:
  • - The windows must match those on the street facing façade of the primary structure in orientation (horizontal or vertical); or
  • - Each window must be square or vertical – at least as tall as it is wide.
  • EAVES: The eaves on the detached covered accessory structure must meet one of the following:
  • - The eaves must project from the building walls the same distance as the eaves on the primary structure;
  • - The eaves must project from the building walls at least 1 foot on all elevations; or
  • - If the primary structure has no eaves, no eaves are required.

Although we still believe there should be no restrictions on the style or aesthetics of an ADU, or any building for that matter, we think the new rules are at least a step in the right direction and we are excited to explore what these new rules allow as we start designing new ADUs.


The updated zoning code and loosening of the design restrictions is great for everyone looking to build an ADU on their property. We have to applaud the Portland City council for their forward thinking and voting to approve the new rules. We also thank all of the people who testified or wrote in to support the adoption of these rules. Without the grassroots advocacy, improvements to our zoning codes wouldn’t happen.

The Zoning Code updates provide more flexibility to the design team by reducing restrictions and hurdles. High quality design increases the value of these structures and should be incentivized and celebrated. Further, the zoning code is about protecting the health safety and welfare of the public and should have absolutely nothing to do with dictating style or aesthetics. The new rules move in this direction and allow creative designers to provide clients with better buildings that fit their unique site and style.

This is especially true for those looking for modern or contemporary styles for their ADUs. We tend to design with a Northwest Modern aesthetic and look forward to exploring the creative flexibility the new rules will permit. This includes the ability to do low pitched or even flat roofs on the smaller ADUs and move towards a very modern look and feel. There is now the opportunity to create wonderful spaces that open up to the outdoors, blending the interior and exteriors. We can also explore rooftop decks and terraces, planted green roofs, and other beautiful and sustainable ideas. We look forward to collaborating with a client who shares in the vision to push the limits of what these new rules allow.


If you want more information on ADUs, our design process or frequently asked questions please visit our Accessory Dwelling Units Design page: http://www.propelstudio.com/accessory-dwelling-units-adu/