Check out this recent article on Crosscut by Jeff Cohen:

Is Seattle ready to take backyard cottages mainstream?


And this new Seattle Times article regarding backyard cottages by Daniel Beekman:

Ruling could pave way for more mother-in-law units, backyard cottages in Seattle


Here is a link that discusses the current city council proposal and the its’ goals:

The city has a nice summary at the bottom I have included for a quick glance: