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

My last post in this series was in September 2019. That was a lifetime ago, it seems. But, legislation and rulemaking takes time, so this series is simply posted at a legislative pace.

Residential Infill Project

On Wednesday, August 12th, the City of Portland finally passed the Residential Infill Project (heretofore, “RIP”). This was an overhaul of single family residential zoning regulations that was nearly five years in the making, and this code will go into effect in August, 2021. Over 12,000 public comments were received in the rulemaking process- a ridiculous amount of public testimony. 

The end result of this residential zoning overhaul was impressive, however. It stakes out a new threshold for residential zoning best practices, putting Portland again on the fore of urban housing and land use. In my estimation, RIP and HB 2001 will be as significant in terms of shaping land use practices Oregon in the 21st century as Oregon’s Urban Growth Boundary legislation was in shaping Oregon in the 20th century. 

Granted, a visible outcome of these new development standards is incremental, and substantial changes to the city will be very slow, for better or worse. But, these incremental changes will be reflective of the types of built environment that the City must have in order to match the needs of the current and future demographic housing compositions. And indeed, many US cities will be compelled by circumstance, politics, economics, and climate change, to make similar adjustments to their residential zoning code in the coming years to set themselves up for a sustainable, 21st century, housing environment. 

Two ADUs in Flexible Configurations

Let’s dive into the changes as they related to ADUs, specifically. Currently, the code allows for one ADU. This code overhaul will allow for two ADUs, built in any configuration. As far as I know, no other city has allowed a 2nd ADU to built in any configuration. That is, the 2nd ADU can be detached or attached, and importantly, two ADUs can also be built in a single detached accessory structure. We’ll see more ‘detached plex’ configurations like this in the future, added to properties with existing single family homes. Notably, if three units are physically attached, that structure is deemed a triplex, not a primary dwelling with two attached ADUs. 

Other places that allow two ADUs, such as California, Seattle, Vancouver BC, and Tigard and Washington County Oregon, all place limitations on the structural form of the 2nd ADU. On the ADU front, RIP stands out in this way, as the flexibility of the additional unit will allow for many more creative infill options. 


If a 2nd ADU is built, one of the three housing units on the property must be ‘visitable’. Visitability is a standard on the gradient of accessibility that essentially enables the housing unit to be visited by someone in a wheelchair. These standards include having no steps to access the unit, 31 3/4” wide doorways, and having a bathroom on the entry level (1005 Type C)

There are some exceptions for sites that don’t have to meet these standards. 

(1) Lots with an average slope of 20 percent or greater;

(2) Lots where there is more than a 3-foot rise between the highest elevation along the street lot line and the lowest grade measured at the front setback.

(3) Conversion of an existing accessory structure that is at least 5 years old or converting space in a house that is at least 5 years old to an accessory dwelling unit.

Off-Street Parking

All off-street parking requirements for the entire residential zone are eliminated. Only a handful of North American cities have made this leap like this, as off-street parking requirements are a political third rail. America is addicted to off-street parking requirements. I applaud Portland for removing this exclusionary regulation that artificially subsidizes automobile transportation costs, by displacing those costs on the back of housing development.

Eventually, other jurisdictions facing an affordable housing crisis will realize this, but it will take years or decades to make this change, and elected city council members who propose this type of change will lose their jobs over it. 

This means that if a homeowner wishes to convert their garage to an ADU, they don’t have to replace that garage with another off-street parking spot. If they DO eliminate their off-street parking spot, they’ll be compelled to close the curb cut, which may cost $2-4K to do. But, that’s just the cost of doing the work, not an administrative cost. 

To be clear, this new policy isn’t just applicable to ADUs; this is applicable to single family homes and middle housing alike. 

Miscellaneous Changes

Other changes are less significant, but positive nonetheless. 

Whereas before, an ADU could only be built alongside a single family house, a detached ADU can now be added to a property that has a duplex. 

Whereas before, a property with an ADU was limited to have a family plus 5 unrelated people, that limitation has been lifted. 

For basement conversion ADUs, the ADU is no longer limited to 800 sq ft. This will allow for a 1,000 sq ft basement to be converted to an ADU, for example, rather than having to somehow artificially constrain the size of the ADU to meet an (arbitrary) 800 sq ft size threshold. 

Lastly, the front entry of an attached ADU can now be on the same architectural plane as the front door of the primary house. Before, the ADU doorway had to be located on a different architectural plane, because it may otherwise look like a (gasp) duplex. 

Middle Housing 

The more significant changes that come with RIP actually don’t deal with ‘ADUs’ but because they’re related, I’ll briefly sketch the changes. The biggest change is that all residential properties may now have duplexes, triplexes and fourplexes, except properties that are within hazard areas. ‘Single family residential properties’ (a mildly insulting and outdated term), will actually be allowed to have up to 6 units if half of them are regulated, affordable housing. 



The development code is switching over to floor area ratio, and using a tiered FAR standard to encourage middle housing. While a new single family house on a 5,000 sq ft lot will be limited to 2,500 sq ft, a new fourplex will be limited to 3,500 sq ft. This tiered FAR has been designed to make middle housing slightly more economically feasible for developers. Without the tiered FAR standard, economic models showed that rational developers would still continue to opt to build large, single family homes instead of middle housing, even under RIP.



The feasibility models indicated that this tiered FAR strategy should help make middle housing more feasible for development, but only time will tell whether the standards are good enough, or if other barriers prevent the development of middle housing (eg. financing, condo defect litigation, market demand). 

The line between middle housing (duplexes, triplexes, and fourplexes) is now officially blurred with properties that also allow for two ADUs. This blurring is a GOOD thing, though admittedly, it will be very confusing for lay homeowner developers to wrap their heads around, as they consider what development options they now have. 

A graphic from Sightline Institute that summarizes some of major residential zoning changes resulting from RIP.

One notable element of this blurring has to do with system development charges (SDCs). SDCs for ADUs are waived, but they aren’t waived for plexes. So, there’s a built in financial incentive to build two ADUs, but not a built-in incentive to do a triplex or fourplex, which may have SDCs of roughly $25K per unit. 

ADUs are required to be small by code, but the tiered FAR standards will effectively drive smaller plex units anyhow. So, there will be some artificial drivers to build two “ADUs” instead of a triplex, for example. Since we generally need to incentivize small housing units, this incentive structure is fine while we observe the actual development typologies that result from RIP, but eventually it may make sense to shift toward an SDC regime to encourage other middle housing options as well. 

Oregon House Bill 2001 (HB 2001)

Meanwhile, at the state level, HB 2001 is making its way through the rulemaking process. HB 2001 was passed into law in November, 2019. It was the top legislative priority for the speaker of the house, Tina Kotek. I sit on the Rules Advisory Committee and Technical Advisory Committee for HB 2001, so have an intimate understanding of how this set of rules is being developed. 

Wiping out Poison Pills for ADU in One Sentence

The impact on ADUs was quick, swift, and frankly, simple. It stripped away the ability for cities to require owner occupancy when building an ADU, and it stripped away the ability for cities to require additional off-street parking when building an ADU…in one sentence. 

SECTION 7. ORS 197.312, as amended by section 7, chapter 15, Oregon Laws 2018, is amended to read:

…(B) “Reasonable local regulations relating to siting and design” does not include owner occupancy requirements of either the primary or accessory structure or requirements to construct additional off-street parking. 

These were the two biggest and most common poison pills for jurisdictions in Oregon (and everywhere else in the country, for that matter), so addressing these controversial issues at the state level was expedient. 

These changes are now in effect statewide, and any city that still has their restrictive rules on the books is now out of compliance. Their rules are no longer enforceable under state law. 

Middle Housing

Taking a page from the RIP rulemaking process, HB 2001 borrowed and expanded on the same guiding concepts, by compelling jurisdictions to allow for middle housing in residential zones by right. 

HB 2001 will have a model code, and a minimum compliance code. Cities must either pass their own residential code that complies with the minimum compliance standards, or it will default to the HB 2001 model code. We don’t yet know how that ‘minimum compliance vs model code process’ will play out in practice. Based on observing the timeline of passing RIP, I suspect that many cities will have a difficult time passing their own HB 2001-compliant code in time, and will instead default to the HB 2001 model code initially, which would actually be a great thing.

The law is weighted to effect jurisdictions differently, depending on their size. Jurisdictions in the Portland metro area and other jurisdictions with more than 25,000 people are subject to the Large and Metro area cities code. Jurisdictions with between 10,000-25,000 are subject to the Medium cities code. 

Medium cities must allow duplexes by right on all residential properties that allow a single family house. The model code allows the 2nd unit to be detached, and it does not require off-street parking. This alone is more middle housing-friendly than any US jurisdiction, let alone any state. 

But, the Large and Metro Area cities model code is even more housing friendly. The model code will allow duplexes, triplexes, and fourplexes on all residential properties, except goal-protected and infrastructure-constrained lands. 

Incremental Plex Development vs Whole Site Re-Development

Plexes can be built in any configuration under the HB 2001 Large and Metro Area cities model code. This means that a homeowner could add a detached duplex structure in the backyard, or a detached triplex structure for that matter, if backyard space and financing permitted, and if the market would bear it. Attached duplexes, triplexes, and fourplexes are still allowed. How middle housing will end up being built remains a fascinating and untested question. As of now, middle housing is commonly developed as attached units by professionals through whole site redevelopment. But, my understanding of the ADU market leads me to believe that the inclusion of detached plexes will be a signficant way that middle housing will be built and that this incremental detached plex approach may be the killer productivity app of HB 2001, where it is allowed. 

On a related note, cottage clusters are also allowed on all residential properties. This means that if space and financing permit, and if the market would bear it, a homeowner could add eight small dwellings on their property, and keep their primary house. 

Attached townhouses all also allowed by right in all residential zones. 

Off-Street Parking

The model code is shaping up to require 1 off-street parking spot for a fourplex on lots under 5,000 sq ft, and 2 off-street parking spots for a fourplex on lots over 5,000 sq ft. In both cases, an off-street parking credit will be given if there’s 22ft of on-street parking available. 

The minimum compliance standards allow for jurisdictions to require more off-street parking, based on a tiered lot size approach. Here’s a sample of how that will look for a fourplexes. 

For Quadplexes, a local government may require up to the following off-street parking spaces: i. For lots of 3,000 square feet or less: one space in total; 

  • ii. For lots greater than 3,000 square feet and less than or equal to 5,000 square feet: two spaces in total; 
  • iii. For lots greater that 5,000 square feet and less than or equal to 7,000 square feet: three spaces in total; 
  • iv. For lots greater than 7,000 square feet: four spaces in total.

(Draft rules for HB 2001, August, 2020) 

Analysis of Impacts Stemming from RIP and HB 2001

Now that I’ve witnessed RIP and HB 2001 first-hand, I would like to make a couple observations intended to help infill housing advocates. 

For Housing Advocates in Oregon 

Under the HB 2001 model code, which is superior to the minimum compliance code in every way from an housing infill advocacy lens, there are a tremendous number of development options. 

The regulatory code will no longer stand as an insurmountable barrier to entry for creative urban infill options. The next large barriers will be space, market demand for the housing type, and financing. 

Our collective addiction to off-street parking requirements will likely result in jurisdictions using the minimum compliance standards. Housing advocates in Oregon should advocate for their planning departments to simply use the model code standard rather than minimum compliance standards. 

Why Don’t We Just Do That?

Here’s some ruminations for advocates and practitioners. Architects, creative developers and builders who enjoy thinking outside the box should consider working in Oregon. And, so should lenders. Because once HB 2001 goes into effect, your imagination will be unshackled. Similar legislative attempts have cropped up in Connecticut, Virginia and California, and I hope they come to pass. 

RIP is incredible, detailed, and inspirational. And, the years of RIP policy legwork provided state legislators with the requisite insight to guide the underlying principles of HB 2001. But, it has taken 5 years to get the code passed. And, RIP only impacts one city with a population of 653,000 people. 

HB 2001 was voted into law in late 2019, and will be in effect statewide in its final form in June, 2022. Whereas RIP took 5 years, HB 2001 went from concept to execution in 3 years, and it will impact 4.2 million people. 

Because I am goal-oriented and impatient, I encourage more ADU and housing advocates to seriously consider state legislative advocacy approaches rather than focusing solely on municipal advocacy efforts. Counterintuitively, statewide approaches like HB 2001 are politically appropriate given the scale and scope of the housing affordability problem, and have more impact than any local regulatory zoning overhaul could have. 

NIMBY dynamics don’t play out as well in state level politics; state level politicians don’t have to listen to as many repetitive comments from community members who fear change. Try to remove off-street parking requirements for any type of development in a zoning board or city council hearing, and you’ll see how inane and intractable that type of process can be. 

Conversely, state legislators are more deliberative and other state-level entities (eg. affordable housing coalitions) are also less parochial about overhauling zoning regulations than say, my neighbors. My neighbors might take the time to attend a local hearing about a middle housing project next door, but they very likely won’t show up to testify about middle housing as a policy matter at the state capitol. 

Let’s hold no illusions that these development forms will become commonplace quickly. As with RIP, HB 2001 wasn’t written to make changes overnight. Rather, these are codes that will really only begin to be visible en masse, decades and even centuries from now. They’re written to decrease the zoning barriers such that the residential real estate market can perform as efficiently and equitably as it can under our Euclidean zoning regime. 

The RIP code is extremely detailed and specific to Portland zoning parlance, but the years of detailed careful drafting will enable RIP to work fairly seamlessly. 

HB 2001 is generically written to work across all cities, and could theoretically be adopted by cities wholesale nationwide. But, it will take years for Oregon cities to reconcile their own codes with the statewide legislation, and it could be fairly messy initially as we gain clarity around specific legal and regulatory interpretations that crop up when the statewide regulations actually go into effect locally in 2022. 

Only time will tell how these efforts will play out, and which of them will have influence elsewhere. But, both efforts are noble, beautiful and appropriate to address the affordable housing challenges of our time. 

And, whatever approach you opt to pursue, you can now point to this post, and just say to your elected official, “Why don’t we just do that?”

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

10 comments on “ADU Legislative Initiatives- History in the Making (Part IV)

  1. David DeFauw
    August 17, 2020

    Hi Kol,
    Thanks for this great overview. At one point, I believe there was a rule in RIP in Portland that the 3rd or 4th unit could only be built on complete streets. Complete streets were defined as having a sidewalk as well as being paved. Is that part of the final rules of RIP?
    Thank you,
    David DeFauw

    • Kol Peterson
      August 17, 2020

      Hi David.

      I won’t attempt to interpret that portion of the code just yet, but read through the commentary on p. 116 of to get a sense of how RIP will treat properties on unimproved streets.

      “33.110.265.E Triplexes and Fourplexes
      Triplexes and fourplexes will be allowed in the R7, R5 and R2.5 zones when
      lots meet minimum lot size standards. Sites that do not have frontage on at
      least one improved street will not be eligible to use these provisions
      because areas with unimproved streets create impediments to access,
      reducing walkability and bikeability. While new development and conversions
      to add units would trigger the need for a street improvement or payment
      of a fee-in lieu (LTIC), the incremental improvements could be mid-block
      and not connect to the street network or may occur elsewhere…”

  2. Danny
    February 12, 2021

    Hi Kol,

    Thanks for the wealth of knowledge and experience you supply on the site!
    With the allowance of a second ADU, are the sizes of each or just one affected by the rule change? For instance, can two ADUs be built that are EACH 75% of the main home? Could a single ADU be built that is bigger than 75% but less than the size two ADUs? (allowing for a nice sized 2-bedroom ADU for instance).



    • Kol Peterson
      February 23, 2021

      Hi Danny,

      Yep, each ADU is limited to 75% of the primary dwelling; no size trading. But, if the primary dwelling is 1,000 sq ft, each ADU can be 750 sq ft.

      Internal basement conversion ADUs can be up to any size, but that’s the only exception the 800 sq ft size limit for ADUs.


  3. Justin
    March 13, 2021

    Kol, it sounds like there’s an opportunity for developers to purchase homes with large backyards and build 2 ADU’s to rent out. As well as increase the value of the home.

    How large must a backyard be in order to build 2 maximum size ADU’s?

    • Kol Peterson
      March 13, 2021

      In theory, you could you do two 800 sq ft ADUs on any lot.

      In practice, it would be easiest to build a stacked flax duplex ADU. And, when doing so, you’d be capped by 15% of the lot coverage. A 5,000 sq ft lot would be mean that you’d be limited to 750 sq ft of lot coverage. Therefor, you’d be far better off to work with a lot that had 6,000 sq ft so that you’d be able to cover 900 sq ft of the lot in accessory structures.

      • Justin Hinh
        March 14, 2021

        Thanks Kol. Another question, can both ADU’s be detached?

      • Kol Peterson
        March 14, 2021

        Yes. Both ADUs can be detached from one another, or attached to each other.

  4. Red
    September 10, 2021

    Hi Kol,
    Wondering if the measurements of the total ADU sq ft is measured from the inside walls or o the outside?

    • Kol Peterson
      September 11, 2021

      Inside walls (in Portland).

Comments are closed.


This entry was posted on August 17, 2020 by in News, Opinion, Policy & Trends.
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