Wash. Rev. Code § 36.70.090
When a commission is created after June 10, 1959, the first terms of the members of the commission consisting of five, seven, and nine members, respectively, other than ex officio members, shall be as follows:
Thereafter, the successors to the first member shall be appointed for four year terms: PROVIDED, That where the commission includes one ex officio member, the number of appointive members first appointed for a four year term shall be reduced by one; if there are to be two ex officio members, the number of appointive members for the three year and four year terms shall each be reduced by one; if there are to be three ex officio members, the number of appointive members for the four year term, the three year term, and the two year term shall each be reduced by one. The term of an ex officio member shall correspond to his or her official tenure: PROVIDED FURTHER, That where a commission, on the effective date of this chapter, is operating with members appointed for longer than four year terms, such members shall serve out the full term for which they were appointed, but their successors, if any, shall be appointed for four year terms.
RCW 36.70.090