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ADU Legislative Initiatives- History in the Making (Part I)

History in the Making

The 24-hour period from the afternoon of Sunday, June 29th- afternoon Monday, June 30th, 2019, was an important day for ADUs. 

In the future, urban planners will point to that day as a signature moment for an era of deregulation and liberalization of codes for ADUs.  

This same day also foreshadowed a growing movement that rejects the entire concept of Single-Family Residential Zoning as we know it, replacing it with a more befitting framework to describe where we live: Residential Zoning

Only time will tell how residential zoning will look in the coming decade, but here’s why that 24-hour period was pivotal in the adoption of ADUs and the concept of single family zoning in US cities. 

What Happened?

In the afternoon of Sunday, June 29th, Oregon’s state senate passed weighty legislation called HB 2001 (“HB 2001”), that effectively ends the concept of exclusive single-family zoning in the state of Oregon. It allows duplexes where standalone homes are allowed, and even allows triplexes and fourplexes in many cases.

To understand the import of that, let’s look back a century to another signature moment in residential zoning history from one century ago. This moment occurred on November 22, 1926 in the form of a decision in a Supreme Court case called Euclid v Ambler. 

That case authoritatively established that certain land uses such as industrial and residential shouldn’t mix. 

The decision of this case catalyzed the dramatic growth of single family residential zoning districts. Strangely, the case was never actually intended to preclude duplexes and missing middle housing types from being developed alongside single family detached dwellings in residential zones. In fact, it took no position whatsoever on the separation of duplexes, triplexes, or fourplexes from single family residential housing types.  

The single family zoning designation which is now so common is falsely ascribed to Euclid v Ambler, and grew in dominance in part based on local legal misinterpretations of that landmark court case. 

In the ensuing century, exclusive single family zoning districts became so widespread that they have to come to accelerate myriad environmental problems ranging from climate change to species loss to construction waste. The economic impacts of single family zoning have been equally influential, initially excluding racial minorities from the intergenerational wealth transfer through redlining, and subsequently obligating jurisdictions to subsidize the tremendous infrastructural costs (ie. roads, sewer, water, transit, schools, fire, police, etc) associated with the geographic sprawl of single family detached homes on large parcels. 

From an economic and environmental vantage, it’s invigorating to see that this Supreme Court case misinterpretation is finally being neutralized (albeit nearly a century later). 

Economic reparations is helping to politically frame this zoning shift. But the devastating impacts of the dominance of single family zoning offer equally compelling environmentally reason to shift away from it. Then, there’s the myriad social, economic, and health impacts associated with the monocropped and antiseptic separation of homes from work and school and retail, which necessitates automobile transport to take care of…well…anything. 

But, this is, not or, so I’m not actually even focusing on the allowance of duplexes, triplexes, and fourplexes in this post. 

The big deal for ADUs is that HB 2001 is the first state legislation to compel cities to entirely drop owner occupancy restrictions and off-street parking requirements for ADUs statewide. 

This means that all cities in Oregon will suddenly go from having a poor-to-fair ADU code to having a good-to-excellent ADU code. 

Up till now, most Oregon cities, like almost all cities in this country, have had poor-to-fair ADU codes. 

When I say that ADU codes are poor-to-fair, in practical terms this means that I personally wouldn’t build an ADU there, and as a professional ADU consultant, I wouldn’t in good faith advise other homeowners to build one either. 

Poor ADU codes are those that require owner occupancy and off-street parking, which are poison pill regulations found in the majority of codes in cities where ADUs are (theoretically) allowed. 

Cities can also often have a number of other (less controversial) development regulations that can also make it challenging to build ADUs, such as limiting the size of the ADU to 50% of the size of the primary house, or requiring 15ft setbacks in side yard or rear yard, or requiring an ADU to be less than 15ft high. HB 2001 does not fix these (less controversial) regulations, but city councils and mayors that want to actually see more ADUs built should be able to fix these problems with less political fallout than the fallout associated with the trite and inane controversy around removing owner occupancy and off-street parking requirements. 

Even with some non-ideal development regulations still lingering, as HB 2001 comes into effect, I would consider building an ADU in every jurisdiction in Oregon, and would certainly advise others to consider it too. 

This is a big deal. When it comes to financial decisions around housing, most adults are pragmatic by necessity. Due to having a flexible code, ADUs have been a pragmatic solution in Portland for nearly a decade, which is why they’ve flourished here-residents like me made individually rational decisions to build one. 

And suddenly with HB 2001, ADUs will become a very pragmatic solution to address individual economic and social needs for average homeowners throughout many cities in Oregon. 

HB 2001 puts ADUs in a position to be built legally in Oregon by removing the primary regulatory obstacles to their development. 

This means that ADUs will finally have a policy test-bed at a statewide level to see where they are actually a relevant and meaningful housing solution. 

Even with excellent ADU codes, ADUs still won’t take off in most jurisdictions. But, they will absolutely take off in more cities that are facing a housing crisis but which have had poor-to-fair ADU codes up to this point. 

From my research, all but five US cities currently have fewer than 1,000 ADUs. I will estimate that 99+%  of US cities have fewer than 100 ADUs. Of those 99+%, I estimate that 3/4s of them have had fewer than 20 ADUs ever permitted. 

These are totally pathetic ADU permit numbers. This is attributable to poor-to-fair ADU codes found in 99+% of US cities. As a result of HB 2001, for the first time in an entire US state, there will actually be observable data about how ADUs perform as a housing option when they aren’t explicitly treated poorly by code. Conversely, much of the current common discourse about ADUs is still based in hypotheticals because of the paucity of data about permitted ADUs. 

Back to June 30th, 2019. 

Within 24 hours of the passage of HB 2001 on the Oregon state senate floor, Seattle passed an excellent ADU code on the afternoon of June 30th after four long years of embattled attempts to do so. This code update eliminates off-street parking requirements and owner occupancy requirements for ADUs. 

This means that ADUs will finally have a better chance at being a meaningful solution in Seattle in the future. As ADUs increase in popularity as a novel grassroots solution to affordable housing problems, observing the change in ADU development trends in Seattle will give policymakers nationally another data trend line to confirm that off-street parking requirements and owner occupancy requirements are the two biggest poison pills to ADU development. 

Eliminating off street parking requirements and owner occupancy requirements puts Seattle squarely in the upper tier of major cities in terms of having decent ADU codes, alongside Vancouver BC, Portland, L.A., and Austin, TX. 

Notably, Seattlites have been flanked to the north by Vancouver and to the south by Portland, two leaders in ADU development. 

Even in Portland, a city with excellent codes and an ADU culture to boot, ADUs are only found on 2% of eligible residential properties. With the passage of Seattle’s latest ADU code, it’s fairly likely that Seattle will surpass Portland in terms of ADU market penetration within the next decade due to its higher land values. 

Seattle’s new ADU code is also significant nationally for another reason: It is the first major US city to allow two ADUs on a property. 

There’s three other cities that I am aware of that currently allow two ADUs, but they are very small jurisdictions by comparison. (Lafayette, Arkansas; Tigard, Oregon; and Gresham, Oregon). So, it’s very significant for a major US city to take this step. 

Vancouver BC, Seattle’s neighbor to the north and recognized leader in ADU development internationally, has allowed two ADUs since 2009. But, now that two ADUs has landed as a new code standard in Seattle, we can reasonably anticipate that other cities (and states) will eventually adopt this best development practice as well.

ADUs are becoming inevitable in many US cities. 

Housing prices in major coastal cities in CA and WA are escalating to the point that in a couple of decades, it will be less and less common for a middle class household in a central city area to afford the monthly mortgage debt service for a typical single family house. To make such properties affordable to the average middle income household, the property will likely need to provide the additional qualifying income that comes from an ADU or two. 

This shift has already occurred in Vancouver, BC where ADUs are extremely commonplace due in part to the tremendously high land costs. Mortgage underwriting practices in Vancouver are designed with ADU income as a factor. Their standards also allow multigenerational family households to aggregate their collective income streams into the purchase of a single residential property. 

The growth of ADUs is an outcome of current housing economics and demographic trends, which are on a predictable collision course with the land use framework of single family residential zoning. 

This regulatory trend seems inevitable to me as more cities confront the history of exclusive single family zoning policy and grapple with their limited options moving forward.  

Even though only five major cities with good ADU codes, the eventual adoption of ADUs as a meaningful new housing strategy in tens or hundreds of US cities seems to me now more a matter of time than anything else. 

What’s Next on the ADU Legislative Frontier?

With the passage of HB 2001, the City of Portland is now highly likely to pass into law a significant code overhaul of single family residential zoning. The Residential Infill Project, as it’s called, will allow up to four units on all “single family residential lots”. 

The Residential Infill Project will allow two ADUs, whether they be detached or attached. Duplexes, Triplexes, and Fourplexes will also all be allowed. 

It also eliminates all off-street parking requirements for development in residential zones.

This is what the future of residential zoning in central city areas should look like. 

If this code is adopted into law, and I am fairly certain it will be adopted now that HB 2001 has passed the Senate, Portland will be the first major US city to likely get there. 

The other major legislative front I’m watching is Senate Bill 13 in California. “SB 13” will eliminate owner occupancy statewide. If it passes, ADUs in California will be in a similar position legislatively as they are in Oregon. 

But, CA is vast market compared to Oregon and every other state in the country, and the high cost of land in many major CA cities presages dramatic growth of ADUs. While ADUs have gained a lot of attention since the 2017 state legislation, most of the jurisdictions in CA are still mired by poor-to-fair ADU codes. SB 13 would significantly change that balance, giving ADUs the chance to shine on a much larger stage than they’ve had up till now. 

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

13 comments on “ADU Legislative Initiatives- History in the Making (Part I)

  1. Mary Senatori
    July 8, 2019

    Thanks Kol — what a fantastic, informative article!

    Do you know how HB2001 plays with historic district designations? I live in Irvington and wonder if existing homes could be converted to up to fourplexes or if undeveloped lots could have fourplexes.

    My assumption is “yes” as long as the remodeled or new structures honor/enhance the historic integrity of the district.

    Thanks, Mary

    On Mon, Jul 8, 2019, 7:33 AM Accessory Dwellings wrote:

    > Kol Peterson posted: “History in the Making The 24-hour period from the > afternoon of Sunday, June 29th- afternoon Monday, June 30th, 2019, was an > important day for ADUs. In the future, urban planners will point to that > day as a signature moment for an era of deregulatio” >

    • Kol Peterson
      July 8, 2019

      Thanks Mary. I would suggest searching for your property here: . Then, you’ll want to talk with the Irvington Historic District land use committee to see what they’re saying about it. Bear in mind that nothing is final yet, so no one will be able to give you the final authoritative answer as to what you could on your property. My best guess is that you can do a fourplex there like everyone else, and that you will be subject to the Irvington Historic District design review process.

  2. Greg San Martin
    July 8, 2019

    Great post, Kol.

    California SB 13 is one of several State bills that would prohibit owner occupancy as a condition of Adu permits.

    AB 68 is another state bill that is interesting. In addition to prohibiting owner occupancy, it would allow two ADUs at single family properties.

    At multifamily properties, AB 68 would allow up to 2 existing detached accessory structures to be converted into ADUs.

    AB 68 would also allow one internal conversion of existing living space at multifamily properties plus an additional conversion of existing living space for every four preexisting units.

    Lastly, AB 68 would allow multiple ADUs to be created from conversion of non living spaces such as attics and basements at multi-family properties.

    There is an important transformation that seems to occur in the mindsets of local agencies once 1% of homes have added in ADUs. Perhaps it is just fear of the unknown, but as your article seems to prove, the 1% club on the West Coast is setting housing policy that seems historically significant.

    I am hopeful that many of the 98% of cities mentioned in your post will soon evolve their thinking and begin supporting ADU policies the same way that leading cities like Portland and Seattle are supporting them. In California, that would lead to an end to ongoing opposition from the League of Cities to progressive statewide ADU policies that fast-track the most sustainable solution to our housing crisis.

  3. Andy Prince
    July 8, 2019

    I would not have built my two ADU’s in Charlotte, NC had the “owner occupancy” requirement been in effect. My understanding is that up until this legislation changed that Charlotte was one of only 3 cities that DID NOT have this requirement. So glad I own two homes and two ADUs! It allows me to live in my home, rent my attached ADU and then rent my other home and it’s detached ADU out to whomever I choose. AirBNB is absolutely KILLING IT FOR ME!!!

  4. Jen
    August 5, 2019

    I thought the main difference between an ADU & a duplex was that with the ADU the main unit had to be owner-occupied. With the elimination of this rule in Seattle what constitutes a duplex rather than an ADU?

    • Kol Peterson
      August 5, 2019

      Jen, the difference is that the ADU is capped at a certain size (eg 1000 sq ft), whereas a duplex unit can be as long as zoning allows the unit to be. Also, many residentially zone areas don’t allow duplexes, but all residential zones allow for ADUs.

      • Greg San Martin
        August 5, 2019

        In California, and I think in all or most places, a conventional second unit is separable (it can be condo’d and sold). ADUs can never be sold separately.

        A bit more in the weeds: in California, we are on the verge of adopting a law that allows multiple ADUs at multifamily properties. A 2 unit property that is a duplex (i.e., with a conventional second unit) presumably will qualify as a multifamily. A single with an ADU or two does not qualify as multifamily.

    • Martin John Brown
      August 5, 2019

      Jen, Kol & Greg — I’d say that for most people, the difference is architectural rather than legal. If we eliminate the unusual circumstance where the developments are being condo-ized, then both the House+ADU and the duplex have a lot in common. In particular, both scenarios involve 2 independent living units on one property, owned by a single owner. The architectural difference is that duplexes tend to be similar in size and prominence, whereas ADUs are almost by definition smaller and/or less prominent than the main house.

      Owner occupancy doesn’t have much to do with this. Some places require owner occupancy, others don’t — that’s a local rule, rather than a defining characteristic of the development. Hope that helps! -Martin

    • Andy
      August 5, 2019

      Depends on the location of the ADU. Different municipalities have different rules.

      I’m in Charlotte, NC and there is no owner occupancy rule. If there were I wouldn’t have built my second one here because I wouldn’t be able to rent it out.

      I believe the adoption rate of ADUs will therefore be driven by this rule in your state.

      Hope this helps.

  5. Pingback: ADU Legislative Initiatives- History in the Making (Part II) | Accessory Dwellings

  6. Pingback: ADU Legislative Initiatives- History in the Making (Part III) | Accessory Dwellings

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This entry was posted on July 8, 2019 by in Policy & Trends and tagged .
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