Yes, some residential lease agreements do need to be notarized in Washington. Leases for a duration exceeding one (1) year must be notarized in order to be valid for the entire duration of the lease (WA Rev Code § 59.18.210).
Leases for less than one year are not required to be notarized. The landlord and tenant may agree to have a shorter lease notarized if they wish, but it is optional for all leases for less than one year.
The information for this answer was found on our Washington Residential Lease Agreement answers.