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The Accessory Structures Zoning Code Update Passed

Good News for Detached ADUs

It is great to see incremental improvements being made to regulatory ADU codes across the country. Austin, TX recently made some improvements to their ADU code, making ADU development more plausible there.

Today, Portland’s had some good news too—the Accessory Structure Zoning Code update passed!

Here is the 102 page description of the regulatory design changes that passed. And here’s my six page downloadable abridged version of the salient changes that pertain to detached ADUs (it’s also embedded below).

View this document on Scribd

Commissioner Fritz had proposed a late amendment that would have prevented ADUs being built within the 5ft setback, but the amendment did have sufficient support, and she withdrew it before the vote. The vote for the update package was 4-1 , with Fritz dissenting. You can watch the 6 minute video here.


Incentivizing Small

  • This update opens the door to a greater variety of design forms of detached ADUs by relaxing their design restrictions.
  • It creates a more streamlined set of regulations for all detached, accessory structures (eg. detached bedrooms, sheds, studios, garages, and ADUs).
  • And, it allows more properties to site detached ADUs where previously the 5’ft setback would have made ADU development impossible without a land use adjustment.

It’s a simple, elegant update that has the potential to incrementally change the face of the detached ADU market in Portland. I’ve already written an editorialized piece about these code updates, so you can read through that piece to understand what these changes may hearken.

Arguably, the most important change is the one that allows for small, detached ADUs to be built within the 5′ setback. This regulatory design change ‘benefit’ is compelling enough that many homeowner/developers will consider whether it makes sense to build an evenProposed ADU changes_6_22_15_Kols_summary
smaller ADU than they were previously planning to build.

For some context here, I’ll digress for a moment on the economics of construction. There is effectively a fixed price to building any new detached habitable unit such as an ADU. Typically, when developing a detached habitable unit, additional square footage is the cheapest part of construction. This is partly why we see so many over-sized homes being built nationally.

So, to advocates of small, affordable, infill housing, it’s refreshing to see a policy that actually provides some regulatory benefits to building smaller, such as this one. The ‘benefit’, in this case, is being able to build within the 5ft setback. It’s notable that this same ‘benefit’ has already been in place for garages. This regulatory code update simply expands this benefit to all other accessory structures.

Improving ADU Codes

It’s too early to say whether this code change will result in more ADU development. What we know for sure is that these codes will make detached ADU site planning and design-development slightly less specialized and nuanced than it has been historically in Portland. Making building ADUs easier is a good thing for affordable housing.

Zoning codes in many places prevent the development of ADUs. Overly restrictive ADU codes are probably the single biggest barrier to ADU development nationally. For other cities seeking to incrementally improve their ADU codes, we’ve provided a model ADU code in a previous post.

About Kol Peterson

Kol is an ADU consultant, advocate and author of Backdoor Revolution: The Definitive Guide to ADU Development. Read more here: and learn about building your own at Email at

9 comments on “The Accessory Structures Zoning Code Update Passed

  1. vrpdxpert
    December 3, 2015

    So glad we can now put the most underused 5 feet in a lot to good use housing people. Bravo Kol, thanks to all the code hackers who fought for this one.

  2. Josh
    December 16, 2015

    Hi there! Can you please offer some clarification of the new, 20′ height guidelines. My understanding of the previous ADU height limits was 18′ at the midpoint of the gable. Will the same, mid-gable, point used as reference for the 20′ height or the highest point on the structure? Thanks for any info you can provide.

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  5. Gail
    January 18, 2016

    Our lot is a 50 x 100 corner lot. Does this mean our Adu must be 20 feet from the side street? Does it mean a unit so could be only 25 feet deep..leaving no room for a small back deck, patio..BBQ area?

    • Kol Peterson
      January 18, 2016

      Gail, this corner part is confusing. I believe you have to maintain a 5′ or 10′ setback from the side street in every circumstance. Then, if you build within the 5′ rear setback (next to your neighbor), you must be 20′ from the street. If you build more than 5′ from the neigbor’s property line, then you do not have to build 20′ from the side street. Basically, you can take best advantage of the small, short ADUs only if it is placed in the corner furthest from the two streets. Make sense?

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This entry was posted on December 2, 2015 by in Design & Build, News, Policy & Trends.
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