PDFWAC 284-24-110
An insurer must make a rate filing to change zip code boundaries.
(1) An insurer must not change an insured's rates solely because the insured's zip code has been changed by the United States Postal Service. This section does not prohibit insurers from using zip codes to define rating territories.
(2) The zip code boundaries approved by the commissioner determine the physical boundaries of each territory. The insurer must make a new rate filing to change the physical boundaries of a rating territory.