ADUniverse 2.0: Pre-approved plans for ADUs and middle housing

The City of Seattle is updating its ADUniverse website with new pre-approved plans for accessory dwelling units (ADUs) and middle housing now allowed throughout Seattle's residential zones.

We invite designers, architects, and homebuilders to submit ADU and middle housing designs that fulfill the criteria and follow the requirements outlined in our Submission Guide.

In January 2026, new legislation took effect for residential areas in Seattle that expands options for accessory dwelling units (ADUs) and other middle housing types. As required under Washington House Bill 1110, all residential properties can now have at least four homes, with greater flexibility for how these homes are designed, configured, and sold. These changes primarily affected Seattle’s Neighborhood Residential (NR) zoning, which has been updated with new standards (see Seattle Municipal Code Chapter 23.44 or this summary of key changes).

We enter this new chapter of housing in Seattle following several years of growth in the production of ADUs after liberalizing our ADU rules in 2019 and launching ADUniverse in 2020. From 2021 to 2025, the City issued permits for nearly 1,000 ADUs each year, a fourfold increase over pre-2019 activity and evidence of high demand for housing choices in residential areas near parks, schools, and quiet, safe streets. Among other resources, ADUniverse includes a gallery of pre-approved ADU plans that offer a faster and more predictable permitting pathway. Since 2020, several hundred permits have been issued for these pre-approved plans.

To support implementation of new NR zoning, catalyze creation of middle housing, and boost housing production, the City of Seattle is updating ADUniverse with a refreshed and expanded catalog of pre-approved plans that reflect the diverse typology of middle housing now allowed throughout our residential zones.