Bellingham, WA Fence Regulations: Retaining Walls (2026)

BMC Chapter 17.10 (Building Codes) adopts the Washington State Building Code under Chapter 51-50 WAC and the Washington State Residential Code under Chapter 51-51 WAC, including the 2021 IBC and 2021 IRC with Washington amendments effective March 15, 2024. The Construction Administrative Code adopted in BMC 17.10.020 carries the IRC R105.2 / IBC 105.2 retaining-wall exemption: a permit is not required for a retaining wall that is not over 4 feet in height measured from the bottom of the footing to the top of the wall, unless the wall is supporting a surcharge or impounding Class I, II, or III-A liquids. Walls over 4 feet, or any wall supporting a surcharge such as a parking area, structure, or another wall, require a building permit and engineered design under IRC R404 / IBC 1807 as adopted by Washington. BMC 20.30.110 (Fences) provides that 'height is measured from the ground level adjacent to the outside edge of the wall or fence' and that 'when fences are constructed on top of walls, both are included in the calculation of height.' That measurement rule applies inside the required yard: the 72-inch interior side/rear yard cap, the 54-inch interior-lot front yard cap, and the 42-inch corner-lot/flanking-street caps include any retaining wall on the outside face. Under RCW 19.27 (State Building Code Act), Bellingham applies the State Building Code Council's standards as written.