In unincorporated Snohomish County, a retaining wall up to four feet high (measured from the bottom of the footing to the top of the wall) is exempt from a building permit unless it supports a surcharge. Walls over four feet, or supporting extra load, need a permit.
SCC 30.50.103(1)(c) exempts retaining walls not over four feet in height, measured from the bottom of the footing to the top of the wall, unless the wall supports a surcharge or impounds Class I, II, or IIIA liquids. Walls taller than four feet, or any wall carrying a surcharge such as a slope or driveway load above it, require an engineered building permit through Planning and Development Services. Where a fence is built on top of a retaining wall, SCC 30.28.040(2) requires fence height to be measured on the uphill side, so a fence atop a wall cannot use the wall to gain extra effective height on the downhill face.
Constructing an over-height or surcharge-loaded retaining wall without a permit is a code violation; PDS may require engineering, permitting, or removal.
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