Seattle is the 18th largest city in the U.S., but it has the nation’s eighth most expensive rental housing market and third largest homeless population. About three-quarters of residentially zoned land is designated for single-family use, but the city wants to increase density. In July 2019, Seattle Mayor Jenny Durkan signed legislation to make it easier for homeowners to develop accessory dwelling units—smaller structures that can house guests or renters—on their properties, with the goal of adding rental housing options while offering a potential benefit to homeowners.
"The short-term goal is simply increasing the number of available housing units, but the longer-term goal is increasing equity,” says Rick Mohler, AIA, a University of Washington associate professor who serves on Seattle’s planning commission. Single-family neighborhoods with ample parks, playgrounds, and other community amenities would become less exclusive.
To help homeowners navigate the regulatory, financial, design, and permitting challenges of developing an ADU, Mohler teamed with city senior planner Nick Welch to create the app ADUniverse. In 2019, they developed a prototype with UW’s Data Science for Social Good program; a slightly modified, public version of the tool, developed by the city government, is expected this month.
With the app, homeowners can see if their lot is eligible for an attached or detached ADU. Existing GIS data on zoning, lot size, and coverage may be enough to produce a yes/no verdict, but more nuanced variables like tree canopy and drainage concerns may prompt the user to contact the city for code compliance help.
Based on the ADU size and type desired, the app prototype estimates the costs of construction, permit fees, architectural design, sales tax, financing, and property tax increases, as well as potential rental income and property value increase, based on the ADU size and type desired. The app prototype also offers a neighborhood-by-neighborhood analysis of demographics and ADU development, and allows residents to see which lots currently have ADUs. However, the public version of the tool will likely not include user-specific financial projections, at least not at its outset.
In conjunction with launching the app to the public, the city is planning to release a set of 10 pre-approved ADU plans to streamline permitting and design. The plans emerged as winners of a design competition that was part of a city-led ADU development reform effort.
—Juror Ming Thompson, AIA
Project Leads: University of Washington College of Built Environments, Seattle . Rick Mohler, AIA; Seattle Office of Planning and Community Development . Nick Welch
Collaborating Organizations: Data Science for Social Good Fellowship; eScience Institute; University of Washington; Seattle Planning Commission
Project Team: Joseph Hellerstein (data scientist), Emily Finchum-Mason, Yuanhao Niu, Adrian Mikelangelo Tullock, Anagha Uppal (data science fellows)
Special Thanks: Seattle Mayor Jenny Durkan, Sam Assefa, Vanessa Murdock, Anissa Tanweer
Title Page Images (architecture firm/photographer): Cast Architecture/Dan Farmer; B9 Architects/William Wright Photography; Best Practice/Ed Sozinho; Microhouse/Bruce Parker, Assoc. AIA; Rick Mohler Architect/Ben Benschneider; Robert Hutchison Architecture/Mark Woods; SHKS Architects/Ben Benschneider