Wash. Rev. Code § 64.90.315
In a plat community or miscellaneous community, if the right is originally reserved in the declaration, the declarant, in addition to any other development right, may amend the declaration at any time during as many years as are specified in the declaration for adding additional real estate to the plat community or miscellaneous community without describing the location of that real estate in the original declaration. The amount of real estate added to the plat community or miscellaneous community pursuant to this section may not exceed ten percent of the real estate described in RCW 64.90.225(1)(b) together with any real estate that is described in the declaration for addition to the plat community or miscellaneous community, and the declarant may not increase the number of units in the plat community or miscellaneous community beyond the number stated in the original declaration pursuant to RCW 64.90.225(1)(c).
RCW 64.90.315