Neighbors Speak: Why Has Portland Led the Way on ADU’s?

In 2010, Portland, Oregon, adopted an ordinance encouraging the construction of accessory dwelling units (ADUs) in single-family homes.  Construction of ADUs immediately began to rise and then spiked, increasing seven times in six years.  Today, ADU permits account for about 10% of all housing permits.  In 2016 the California legislature passed legislation mandating local regulation of ADUs in a form that parallels the Portland model.[1]  Could a spike in ADU construction for single-family homes be on the horizon for San Francisco?  It depends on the manner of implementing the state law.

The Portland ordinance, as amended in 2010, provides a flexible framework for the architectural design of ADUs.  The most essential provisions relate to size and location.  For example, the size of an ADU “may be no more than 75 percent of the living area of the primary dwelling or 800 square feet of living area, whichever is less.”[2]  Detached ADUs may not occupy more than 15% of the lot area and must be behind the rear wall of the house and set back 40 feet from the front lot line.  ADUs attached to the primary residence may share a common entranceway.

With such mild restrictions, ADUs are permitted in the “great majority of single-family lots”[3] and have displayed a highly individualistic character, reflecting the taste, preferences, and quirks of the primary homeowner.  The most common form of ADU has proved to be the detached unit suited to the suburban pattern of land use in much of the city.  About one fifth of the ADUs, however, are attached to the primary residence as a wing or backyard addition.  In a city with many free standing garages, homeowners have also found creative ways to construct ADUs above and adjoining a garage structure.

The city of Portland has actively promoted ADUs by providing technical assistance, workshops, and tours of individual homes.  Since 2010 the city has waived development fees for permits that meet certain generous criteria, and it processes applications as a matter of right with limited design review, or none at all, depending on the location and type of ADU.

The California legislation enacted in 2016 mandates that local governments adopt ordinances following precisely the same format as the Portland ordinance: the size of  “an attached accessory dwelling unit shall not exceed 50 percent of the existing living area” or “1200 square feet.,” which ever is less.  And the size of  “a detached accessory dwelling shall not exceed 1200 square feet.”[4]  Like the Portland ordinance, the Legislation places certain limits on fees for utility connections and requires ministerial approval “without discretionary review or a hearing” of all permit applications within a period of 120 days.[5]  But as a state law rather than a local ordinance, the legislation has two aspects that distinguish it from the Portland ordinance; the law provides an avenue for local modification of the mandated standards and a unique system of enforcement.

The leeway to modify the standards of state law is found in a provision giving the local government the power to “impose standards of accessory dwelling units that include, but are not limited to, parking, height, setback, lot coverage, landscape, architectural review, maximum size of a unit,…”[6]  An interpretative memorandum of the California Department of Housing and Community Development, explains that “a local government may reduce the maximum unit size below 1,200 square feet so long as the requirement is “not burdensome” and does not “unreasonably restrict opportunities” to build ADUs.[7]  It mentions 800 square feet as a possible maximum unit size.  In San Francisco, a maximum unit size of 700 square feet would probably pass the bar of state law.

Although the memorandum does not itself have the force of law, it provides an entirely reasonable interpretation, and it can doubtlessly be applied in other contexts.   Setbacks and lot coverage requirements in particular can dramatically curtail opportunities for ADU construction.  Accordingly, they must be tailored so as to avoid unreasonably restricting such opportunities.  How this is to be done presents a complex issue.  A limitation that is appropriate in the Richmond District may unreasonably restrict ADU construction in Bernal Heights or Telegraph Hill.  The state law contains only one provisions affording guidance: “No setback shall be required for an existing garage that is converted to an accessory dwelling unit, and a set back of no more than five feet from the side and rear lot lines shall be required for an accessory dwelling unit that is constructed above a garage.[8]

On its face, the state legislation may appear to have a weak, even quixotic enforcement mechanism.  It states that an ordinance regulating ADUs that “fails to meet the requirements of this subdivision … shall be null and void.”[9] Homeowners may rely directly on state law in applying for ADU permits if a local government fails to enact an ADU ordinance or adopts provisions that are void under state law.[10]  In effect, the law establishes a system of self-regulation.  Local governments are expected to comply with state standards or face the confusion of conflicting local and state requirements.  The system unquestionably opens the door to evasion of state law, but it is probably wise.  The urban landscape of California is so varied that rigid state-wide standards would inevitably cause mischief at a local level.


A detailed study of the Portland ADU success story by the Terner Center for Housing Innovation finds that “websites, events, and tours promoting ADUs .. have a high ‘bang for buck’ ratio; they cost very little but can have a surprisingly large impact.”[11]  But the Portland experience also shows that promotion succeeds where there is an attractive product to sell.  ADU permit requirements must accommodate the individual needs and preferences of homeowners.

The 2016 amendments set the stage for creation of ADU-friendly ordinances at the local level.  San Francisco took a first step to comply with state law on May 12 when it adopted ordinance 95-17 calling for ministerial approval of a certain category of ADU applications.  But there is much more work to be done.  The San Francisco ADU Manual offers no prototype for the sort of backyard additions that would probably be the most popular form of ADU in the Richmond District where I live. The four prototypes for single-family homes now included in the Manual each contain disincentives, or outright obstacles, to ADU construction.  Still, they point the way to an efficient mode of regulation to the extent that they offer a rudimentary kind of form-based coding.  The city may draw on the expertise of practitioners of form-based coding to create a new set of prototypes conforming to state law and the desires of homeowners.

Michael Murphy worked for roughly 20 years as a research attorney for the California Court of Appeal, First District, serving first as an aide to Justice William Newsom. He has degrees from Harvard College and Stanford Law School. In the past 12 years, he has written nine law review articles in well known journals including the Santa Clara Law Review, the NYU Journal of Law and Business, the Virginia Law and Business Review, The Business Lawyer, and the Delaware Journal of Corporate Law.


[1] Now codified as Gov. Code section 65852.2.

[2] Title 33, Planning and Zoning, section 33.205.040 C.3.

[3] Accessory dwelling units in Portland Oregon: evaluation and interpretation of a survey of ADU owners, Martin J. Brown andJordanPalmeri, p. 6, (Oregon Depart of Environmental Quality, 2014)

[4] Gov. Code section 65852.2(a)(1)(D)(iii) and (iv).

[5] Gov. Code section 65852.2(a)(3). The requirement of ministerial approval has the effect of removing ADU applications from review under the California Environmental Quality Act (CEQA).  Public Resources Code section 21080(b) states that CEQA does not apply to ministerial projects to be carried out or approved by public agencies.

[6] Gov. Code section 65852.2(a)(1)(B).  Section (a)(8) expressly provides that ADU applications may not be subject to standards for “allowable density.”

[7] California Department of Housing and Community Development, Accessory Dwelling Unit Memorandum, December 2016, pp. 9-10.

[8] Gov. Code section (a)(1)(D)(vii).

[9] Gov. Code section 65852.2(a)(4).

[10] Gov Code section 65852.2(b)

[11] Karen Chapple, Jake Wegmann, Farzad Mashhood, and Rebecca Coleman, Jumpstarting the Market for Accessory Dwelling Units: Lessons Learned from Portland, Seattle and Vancouver, pp 19-20 (Terner Center for Housing Innovation, UC Berkeley, 2017)

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