As mentioned in the ‘How Does It Work?’ section, promoting ADUs is accomplished by making changes to your local zoning codes and, as a result, ADU regulations vary substantially from community to community. This diversity in the goals and motivations of ADU regulations makes it difficult to evaluate how successful ADUs have been in general way. However, several states facing high growth rates and housing shortages, particularly those on the west coast, have enacted statewide legislation promoting the development of ADUs. The results of these statewide efforts have been mixed and have often required successive fine-tuning of legislation. The rest of this section discusses the experience with ADUs in the states of California, Washington, and Oregon and highlight lessons that can help your community get the right ADU regulations that best meet its unique needs.

California

In 1982 California enacted its ‘Second Unit Law’ (Government Code 65852.2) to encourage the development of ADUs. The legislation authorized local governments to authorize the creation of ADUs by enacting a local ordinance. If local governments chose not to enact such an ordinance, they were required to approve all ADUs that met state standards. Those cities and counties that adopted an ordinance had a great deal of leeway in establishing their own criteria for second-unit applications as well as determining the approval process. All of the communities in California that enacted second unit ordinances chose ‘conditional use’ permitting, which gave communities greater discretionary control over ADUs. With the conditional use approach, ADUs were not allowed as a matter of right, but subject to an often prolonged and contentious approval process that included environmental review of the project and one or more public hearings.

Not unexpectedly, the number of ADUs built in California under the 1982 ‘Second Unit Law’ was far lower than expected. For example, a report produced by Sunnyvale’s planning department noted only five applications for ADUs processed in 2002, eight in 2001, and ten in 2000. A 2002 survey conducted by the Local Agency Formation Commission (LAFCO) confirmed that the number of ADUs built in other communities throughout the state were similarly low. Of the 475 cities asked the survey question

“How many second units (granny flats) were approved in your jurisdiction in 200,” only 229 cities (or 48%) responded to the question, suggesting that more than half of

California communities didn’t even approve one application for an ADU that year (let alone get any ADUs built). The survey further showed that among those 246 cities (or 52%) that did approve at least one ADU unit in 2001, a total of only 658 applications were approved. While this averages out to less than three (2.87) ADUs approved in those cities that approved at least one ADU, the average number of approved ADU applications per city was actually lower than it appears in aggregate. This is because just two cities processed almost 21% of the ADU applications approved that year: Carlsbad alone was responsible for 100 followed by Santa Rosa with 47. (The high number of ADUs in Carlsbad was primarily a product of the city’s inclusionary zoning ordinance [see the Inclusionary Housing tool], which mandates that 15% of all approved residential units be affordable to lower income households. The development of ADUs was one of the available options for satisfying that mandate).

In an effort to remove some of the regulatory obstacles to ADUs and improve certainty and predictability in the development approval process for ADUs, the California legislature passed AB 1866 in 2003, which prohibits a conditional-use type of discretionary review and/or public hearing for proposed ADUs that was so prevalent under the ‘Second Unit Law’: as of July 1, 2003, California communities must consider ADUs ministerially (i.e., the review process must involve only quantifiable, fixed, and objective standards rather than discretionary ones). That is to say, ADUs must now be allowed ‘by right’ throughout the state, so long as they conform to pre-defined objective standards set out in the local zoning code. The bottom line: by eliminating the time consuming, intimidating, and costly public notice and hearing required by the old conditional use approval process, the law in California now removes one of the major barriers that many communities had used to prevent ADUs from getting built.

Because AB 1866 is so new, it is too soon yet to tell whether making ADUs a permitted use allowed by right will be enough to increase the number of ADUs in California (or whether further amendments and fine tuning will be required). According to Marc Brown, a staff attorney for the California Rural Legal Assistance Foundation, more still needs to be done: "The existing law [AB 1866] pretty much leaves it up to local governments as to what standards will apply to second units. This [law] will only address part of the problem, which is procedural. It doesn’t really address the substantive conditions that local governments can apply [to ADUs].” In other words, communities still have significant power to severely limit the number of ADUs that they allow: cost-generating design requirements, burdensome parking regulations, or overly generous minimum lot sizes can deter many homeowners from building an ADU (see the ‘How to Put this Tool into Action in Your Community?’ section for information on how to avoid ‘back door prohibitions’ such as these in order to get meaningful and effective ADU regulations in your community). For instance, the city of Moraga stipulates that secondary living units may not be on adjoining lots unless they are a minimum of 500 feet apart, thereby requiring either very large lots for ADUs or limiting them to every other lot. To address the problem of communities imposing excessively restrictive standards on ADUs, a separate bill (AB 1160) outlining an acceptable range of ADU standards will be heard in the California Assembly’s Housing Committee sometime in 2004. In the meantime, homeowners and developers who have been frustrated in the past with getting approval for their ADU applications hope to have better luck under the AB 1866 and communities facing persistent and critical affordable housing crises are anticipating that the law will encourage increased construction of ADUs and help relieve their local and/or regional affordable housing shortages.

Washington

In response to its rapidly growing population, Washington passed its Growth Management Act (GMA) in 1990 requiring that the state’s fastest growing cities and counties plan in adherence with state goals. The state goals included sprawl reduction, concentrated urban growth, and affordable housing.

The GMA was followed in 1993 by the Housing Policy Act (HPA), which established the dual goals of reducing the cost of housing and improving the quality of the housing stock for all income levels. Encouraging the development of accessory apartments in existing single-family homes was recognized as a major component of realizing those goals. HPA required counties planning under GMA and cities with populations of over 20,000 to adopt ordinances that incorporated the accessory apartment recommendations developed by the state Department of Community, Trade, and Economic Development (DCTED). The recommendations were the result of a DCTED survey of existing ordinances and regulations related to ADUs and identification of barriers to their placement.

Since 1994, most cities, even those not governed by GMA, have adopted ADU ordinances to comply with the HPA. Indeed, some communities, such as Mercer Island, have depended heavily on ADUs to meet growth management goals. (For more information, see the case study of Mercer Island in the ‘Who Else Is Doing It?’ section.)

Oregon

Oregon’s Metro Regional Government had already mandated the use of ADUs, but the Metro Affordable Housing Technical Advisory Committee (H-TAC), in preparation for a Regional Affordable Housing Strategy Plan, decided to find out if local governments were using other tools to encourage the development of affordable housing. In September 1999, H-TAC surveyed 24 cities and 3 counties in Oregon and learned that with the exception of Portland, very few jurisdictions use more than one or two affordable housing tools. Moreover, tools that were mandated by Metro, namely accessory dwelling units, were used twice as often as tools not mandated by Metro.

The bottom line on ADUs’ impacts. In the three case studies above, state requirements seemed necessary to push local communities to include ADUs as part of their affordable housing program. Local communities on their own seem reluctant to initiate changes to the zoning code that would encourage ADUs due to concerns over potential neighborhood opposition to ADUs. For the most part, however, once local communities are directed by statewide requirements to create meaningful ADU regulations, most communities do try to comply with the spirit of the law despite some the fears of some residents that encouraging ADUs will result in a flood of such units that will lead to overcrowding, parking shortages, and other problems that will lower property values and undermine the character of existing single-family neighborhoods. However, as the rest of this section makes clear, this fear is unfounded: well-crafted ADU regulations provide new housing in a balanced, incremental fashion, so that the units are integrated into the fabric of the existing neighborhood.

Of course, the number of ADUs that are likely to be built will vary with each community and is related to such factors as current vacancy rates and housing demand characteristics as well as the restrictiveness of the community’s zoning regulations. However, the experience of communities that have legalized and/or encouraged ADUs seems to indicate that the actual number of ADU conversions in established neighborhoods is likely to be relatively low (more like a trickle than a tidal wave). For example, the Planning Director of the City of Pleasanton (CA) noted that only a handful of ADUs have been retrofitted into existing neighborhoods in Pleasanton, but that ADUs are becoming quite common in new neighborhoods. In fact, a national survey of 47 communities published suggests that communities with zoning “favorable” to ADUs can expect the creation of approximately one ADU per 1,000 single-family homes per year (from “Accessory Units: An Increasing Source of Affordable Housing,” by Patrick H. Hare and John Danbury, in Public Management, v73, Sept. 1991, pp 5-8).

Based on other communities’ experience with ADUs and the anecdotal and survey evidence discussed above, it appears that allowing ADUs in single-family neighborhoods can be an important part of a community’s affordable housing strategy but that it will not generate significant numbers of housing units by itself. The lessons for your community are these: while allowing ADUs in your community will not bring about the demise of established neighborhoods as some residents may fear, ADUs can also not be relied upon to solve all of the housing problems in your community. However, ADUs can be one critical piece of your community’s efforts to create more housing and can be very effective in conjunction with other policies that increase the supply of affordable housing (such as the Housing Incentives Program; Incentive Zoning; Inclusionary Zoning; Infill Opportunity Zones; Development Exactions; Reduce/Eliminate Parking Requirements). For information on how to craft effective and balanced ADU regulations where you live, check out the next section ‘How to Put This Tool into Action in Your Community.'