The City’s accessory dwelling units (ADU) regulations were recently updated, by Ordinance 125854, and went into effect on August 8, 2019. The updated regulations removed the owner occupancy requirement for ADUs.
The City of Seattle wants to remind homeowners of the grace period through June 30 for legalizing existing unauthorized backyard cottages. Under new regulations that went into effect December 4, 2009, backyard cottages became legal throughout Seattle. Previously, backyard cottages, also known as detached accessory dwelling units or DADUs, had been allowed only in southeast Seattle neighborhoods since 2006. Included in the December legislation is a grace period that allows owners of existing, unauthorized backyard cottages the opportunity to legalize their unit without penalty. Owners have until June 30, 2010 to apply for a building permit and until December 31, 2010 to obtain final inspection of the unit.