Most retaining walls require building permits. If the wall is retaining more than four feet of soil measured from the bottom of the footing to the top of the wall or has a surcharge on the wall then it must be reviewed by a WA State licensed engineer.
Two sets of plans are required for submittal including a site plan with location of walls and detailed section view showing construction of wall. See Submittal Process and Required Plans for full details.
Submittal must comply with land use requirements (critical areas, shorelines, flood, steep slope hazards, etc.)
Exempt from Permit
Retaining walls that are less than 4 feet in height measured from the bottom of the footing to the top of the wall, and have no surcharge on them are exempt from a building permit only. The wall must comply with all other regulations and may require permits from the Natural Resources Division.