Turning a single-family into a multi family in Seattle Wa

[Luis Felix]

 My dad is selling one of his two properties in the Phinney Ridge District of Seattle. I have tried to talk him out of it, but that’s a whole other topic.  My question is, can my dad add a second unit to his single-family home? It has a Unfinished basement. And what would the permits cost? 

[Michael Haas]

The rules seem to be changing with the recent reccomendations around ADU's and DADU's. For now most people adopt the approach Brian mentions:

Originally posted by @Brian Hughes:

As for forgiveness instead of permission after getting caught