A “20-day” notice may only be used to terminate a month to month tenancy. It does not terminate an unexpired lease.
The 20-day notice to terminate tenancy must be served at least twenty days in advance of the last day of a rental period and must terminate the tenancy as of the end of the last day of a rental period. The date of termination is not calculated by adding twenty days to the date it is served.
After the termination date if the tenants still have not vacated the process is the same as for a 3-day notice to pay rent or vacate and/or 10-day notice to comply or vacate. The landlord may not change the locks or call the sheriff at the end of the termination period. Instead, as mentioned, the landlord must follow the exact same court process as for other types of notices.
In Seattle all tenancies, including month to month tenancies, require just cause. A landlord may not terminate an unexpired lease, for example, because the landlord is selling the property or wants to move in the property.
For use in Washington outside Seattle -
For use for residential properties in Seattle -