Wash. Rev. Code § 18.85.241
A designated broker may apply to the director for authority to establish one or more branch offices under the same name as the real estate firm upon the payment of a fee as prescribed by the director by rule. The director shall issue a duplicate license for each of the branch offices showing the location of the real estate firm and the particular branch. Each duplicate license shall be prominently displayed in the office for which it is issued. Each branch office shall be required to have a branch manager who shall be a managing broker authorized by the designated broker to perform the duties of a branch manager.
A branch office license shall not be required where real estate sales activity is conducted on and, limited to a particular subdivision or tract, if a licensed office or branch office is located within thirty-five miles of the subdivision or tract.
RCW 18.85.241