Because Washington is experiencing a housing affordability crisis, the Washington State Legislature passed House Bill 1337 which aims to diversify housing types on residentially zoned land to create more affordable housing and start to correct for historic economic and racial exclusion. (source) 

What does this mean for Seattle?

Along with updating the existing ADU code in compliance with HB 1337, Seattle will implement new rules to promote building ADU's. These include flexible design standards, a flexible permitting process, no street improvement requirements, two ADU's per lot, and increased maximum ADU size, to name a few. (source)

Hopefully, we will see more ADU's and affordable housing in the near future!