Empowering Residents: Advancing Seattle’s Accessory Dwelling Unit Strategy

BY MATTHEW LEGER • March 3, 2022

In October 2020, WalletHub ranked Seattle number two on the list of fastest growing large cities in the United States. As host to headquarters of two of the world’s most valuable companies (Amazon and Microsoft) and with a rapidly growing economy, the city’s population and wealth has exploded in the last decade. Despite tremendous efforts to increase housing production to support this growth, demand persistently outpaces supply by a significant margin. As a result, Seattle continues to struggle with a crippling housing crisis.

In an effort to curb the emerging housing crisis in 2014 and 2015, Seattle convened a task force of housing experts across the public, private, nonprofit, and social justice sectors, a diverse set of stakeholders typically at odds over key housing issues and solutions. Over the course of ten months, the task force came up with a comprehensive list of 65 recommendations to establish what would become known as the Housing Affordability and Livability Agenda -- or HALA. Designed to address the city’s housing challenges --including issues related to land use and zoning regulations, resources for affordable housing, subsidized housing development, and permitting processes-- the task force established high level guidance for city agencies to increase housing production.

Seattle’s Office of Planning and Community Development (OPCD) was tasked with implementing several of HALA’s recommendations. One small but important focus area for OPCD was centered around accelerating development of Accessory Dwelling Units (ADUs) in single-family lots.

ADUs a small but important pillar of Seattle’s housing production efforts

ADUs are small, secondary living units allowed in residential areas. ADUs are often used by property owners to provide separate living space for family/friends or as rental units. Seattle distinguishes two types of ADUs:

  1. Detached Accessory Dwelling Units (DADUs) - ADUs located in a separate structure from the main house on a lot. These are often referred to as backyard cottages or carriage houses.

  2. Attached Accessory Dwelling Units (AADUs) - ADUs located within or attached to the main house on a lot. These are often referred to as in-law apartments or basement suites.

All cities in Washington State have been required by law to allow AADUs on qualifying properties since the 1990s. Seattle began piloting DADUs in the mid-2000s and in 2010 they expanded their DADU policy citywide. Despite some communities initially fearing that allowing ADUs citywide would unleash a wave of construction in backyards across town, from 2010 to 2014 Seattle saw only about 40 DADU permits per year in a city with more than 120,000 single-family lots. In other words, the city had experienced very little DADU development compared to the scale of the opportunity.

While the full potential of ADUs had not yet been reached in Seattle, OPCD saw them as one important tool that is part of an overall approach to housing access, choice, and affordability. “Given the enormity of our housing shortage, we try to be very clear that ADUs are unlikely to move the needle in a significant way,” said Nick Welch, senior planner for OPCD, but he still believes that they make up a small but important piece of the solution to a much larger and more complex housing problem.

To better understand why ADU production was so low, in 2015 OPCD set out to engage residents to understand the barriers they face in pursuing ADU development on their property. They spoke with homeowners, especially existing and prospective ADU owners, and also held discussions with design and construction professionals. Through these discussions, OPCD identified several key challenges residents were facing related to regulatory and zoning barriers that made it difficult for them to develop an ADU on their properties.

Using this feedback, OPCD developed a new proposal for zoning regulation changes designed to remove the barriers identified by residents in the engagement process. It took several years for OPCD to outline the proposal and implementation was delayed due to several legal challenges; fortunately, the proposal passed in 2019, paving the way for increased ADU production, which is currently underway.

A centralized hub for all things ADUs

In addition to regulatory and zoning barriers, residents also noted challenges like lack of access to financing (especially for lower-income residents) and the complexity of the ADU design and permitting processes. In response to this, OPCD sought to centralize and simplify the information on ADUs to provide essential resources and guidance to residents. The aim was to provide proactive resources and support to help residents navigate the process and accelerate ADU development activity. “We wanted to provide people with resources that help them understand key steps in the ADU development process and identify financing and professional resources that are available to help them,” said Welch.

One resource OPCD wanted to provide was a tool to help residents quickly determine whether it was even possible to build an ADU on their property. So, in 2018, OPCD partnered with the University of Washington’s (UW) Data Science for Social Good project to explore ways to leverage the city’s existing housing data to help support ADU activities in Seattle. Together, they used zoning, permitting, and property data to develop a search tool (see below) that residents can use to determine whether their property is a potential fit for an ADU. According to Welch, while the tool cannot provide definitive answers about development regulations, it uses several datasets to assess a property’s suitability for an ADU, identifies potential challenges, and helps property owners understand next steps.

Screenshot of main ADUniverse page with map of Seattle and text "Where can I build on my lot?"

With new ADU rules in place, in September 2020 OPCD launched ADUniverse, a hub site that centralizes information and resources a resident may need to pursue ADU development (see below). Site visitors can access a step-by-step guide to creating an ADU, explore a gallery of 10 pre-approved DADU designs or the property search tool, and view an interactive dashboard tracking ADU permitting activity across the city. When ADUniverse launched, thousands of users flocked to the site to learn more. In the past twelve months, the site has averaged nearly 300 daily users thanks to ongoing interest in ADUs, plus proactive promotion of the site through the city’s social media platforms, partners like UW and the local chapter of the American Institute of Architects (AIA), public engagement activities such as ADU fairs, and OPCD sponsored newsletters.

ADUniverse screenshot showing tabs for exploring the data, checking out pre-approved plans, and the definition of an ADU.

An increase in ADU development activity

In the last two years since the new zoning regulations were in place and ADUniverse was launched, Seattle has seen a substantial uptick in ADU development. In 2019, the City issued 286 ADU permits, in 2020 that number nearly doubled to 502, and in 2021 that number increased to 800.

Welch noted that breaking down regulatory/zoning barriers, simplifying the permitting process, and providing centralized resources through ADUniverse all played an important role in accelerating ADU activity. However, he also noted that shifts in the housing market and impacts from COVID-19, such as an uptick in residents working from home, may have also had a significant impact.

Since residents had identified regulatory barriers and burdensome permitting processes as key challenges preventing them from pursuing ADU development, Welch believes that increased permitting and construction activity “are all good signs that what we have done has helped build momentum around ADUs.” He went on to note that residents have reacted positively to ADUniverse, finding it a helpful resource for those just starting on their ADU journey. Also, by providing proactive information resources to residents, OPCD has been able to spend less time helping residents navigate the process and focus instead on advancing the city’s overall housing strategy.

Advice for other local governments pursuing an ADU strategy

For other local governments in the US considering pursuing an ADU strategy, Welch offered two key pieces of advice:

  1. Listen to constituents. Before embarking on an ADU strategy, listen to your constituents to determine what will truly be helpful. Welch believes that the legal challenges that delayed adoption of new ADU regulations were, in part, a blessing in disguise because “it offered us an opportunity to hear more about the challenges residents were facing and their motivations for building an ADU, and to expand and tailor our policies and programs to help them.”

  2. Target those most in need. Welch emphasized the importance of race and social justice in OPCD’s work. “We know that, historically, homeowners able to build an ADU are disproportionately white and wealthy and that these development types are less accessible to low-income families and households of color” and it's important to remember who is most affected by our housing challenges. He continued, “Government energy should go towards the greatest need. That can mean focusing broadly to create more housing options and choices, but also having a pretty targeted approach to helping those that face the greatest barriers and who could most benefit.”

Looking ahead over the next few years, OPCD plans to continue their efforts to advance their ADU strategy and to evolve their programs and services. In 2022, Welch is leading an effort to survey ADU owners and occupants to better understand demographic trends, socioeconomic circumstances, personal motivations, and their experience developing an ADU on their property. And as the city looks to update their 20-year comprehensive plan, Welch is hoping to take the lessons learned from this experience to find new ways to empower residents. “Removing regulatory barriers and centralizing resources through our hub were important steps for us to take, but just leaving residents, especially lower-income households, without more support after these changes are in place does not fully empower them to be true participants in the city’s growth and change.” He hopes the city can provide more resources and programs to residents that go beyond ADUniverse so that more residents, especially lower-income households of color, can not only become a part of, but actually help to create, a more equitable Seattle.


About the Author

Matthew Leger

Matt Leger is a Research Assistant for the Innovations in Government Program at the Ash Center. He has a diversity of experiences in research across the public and private sectors, as well as in academia with a primary focus on understanding how technology can be used to help address some of society’s greatest challenges. Matt has worked with the Smart Cities Strategies team at the International Data Corporation (IDC); the NYCx team in the NYC Mayor’s Office of the Chief Technology Officer; and at the research institute CTG-UAlbany. He holds a Bachelor of Arts in Public Policy and a Master’s Degree in Public Administration both from the Nelson A. Rockefeller College of Public Affairs and Policy at the University at Albany in Albany, NY.