Retaining walls over 4 feet tall (measured from footing bottom to wall top) or supporting a surcharge require a building permit and engineered design in Redmond under IBC and RMC 15.06.
Redmond adopts the International Building Code (IBC) and International Residential Code through RMC 15.06. Retaining walls require a building permit when the wall exceeds 4 feet in height measured from the bottom of the footing to the top of the wall, supports a surcharge such as a driveway or structure, is located in a critical area or steep slope zone, or is composed of stacked block or masonry over 3 feet. Engineered plans signed by a Washington-licensed civil or structural engineer are required for permits. Tiered walls must have a horizontal separation equal to twice the height of the lower wall to avoid being treated as a single combined wall. Walls within critical areas (landslide hazard, erosion hazard, wetland buffer, or Sammamish River floodway) require additional environmental review. Setbacks are typically 3 feet from a property line for walls over 4 feet. DIY stacked landscape blocks up to 3 feet total height are generally exempt from permits.
Unpermitted retaining wall over 4 feet: stop-work, fines doubled or triple permit fee, and possible requirement to remove or redesign wall at owner expense.
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