Seattle Detached Accessory Dwelling Unit Permits Since 1990

Seattle permit records for building permits that create or demolish detached accessory dwelling units (DADUs), beginning in 1990 and updated through the current quarter. The dataset contains records for permits that are either completed or currently issued, compiled by the City of Seattle.

Use Cases

• Analyze trends in DADU construction and demolition permit activity over time to assess housing policy impacts.
• Study the evolution of regulated housing unit types, such as the introduction of small efficiency dwelling units in 2016.
• Examine permit density by address, as there may be multiple permits for any given location.

Strengths

• Temporal coverage spans over three decades, from 1990 through the current quarter.
• Data is sourced directly from the City of Seattle's official permitting system.
• Available in multiple formats including CSV, JSON, and XLS for flexible access.

Limitations

• Records exclude permits that were issued but not completed, making it non-comparable to permit issuance statistics.
• Housing unit type classifications are not standardized and reflect the codes in effect at the time of permit issuance.
• A single building permit may appear as multiple records if the project involved a mix of unit types.

Provenance

Source

City of Seattle permitting system.

Collection Method

Extracted from the city's building permit records for DADUs.

Time Range

1990 through the current quarter.

Freshness

Updated quarterly, with the last update in March 2026.

Geography

City of Seattle, Washington, United States.