In unincorporated King County, an above-ground pool that can hold water more than 24 inches deep is regulated as a swimming pool under the Washington State Residential Code Appendix G/AG105 (WAC 51-51). It requires a building permit and a barrier at least 48 inches tall. The pool wall can serve as the barrier when it is 48 inches or taller, but ladders must be removable, lockable, or secured.
King County adopts the Washington State Residential Code (WAC 51-51), which incorporates IRC Appendix G - Section AG105 for residential pool barriers. The code defines a swimming pool as any structure intended for swimming or recreational bathing that contains water over 24 inches deep, so an above-ground or inflatable pool exceeding that depth is regulated and requires a King County building permit. AG105 requires the top of the barrier to be at least 48 inches above grade measured on the side facing away from the pool, with no more than 4 inches of clearance below and no openings allowing a 4-inch sphere. Where the above-ground pool wall is 48 inches or more tall on the entire perimeter, the wall itself can serve as the barrier; in that case, ladders or steps must be removable, lockable, or otherwise secured when the pool is unattended, or surrounded by a separate compliant barrier. Electrical work for pumps and heaters requires a Title 16 electrical permit and must follow NEC Article 680. Pools on parcels with critical areas under K.C.C. Chapter 21A.24 (wetlands, streams, steep slopes, shoreline) may need additional review. Confirm with King County DLS - Permitting at 206-296-6600.
Installing an above-ground pool deeper than 24 inches without a building permit, leaving a fixed access ladder available when the pool is unattended, or having a pool wall under 48 inches without a separate compliant barrier violates WSRC AG105 and supports a stop-work order, a failed inspection, and a code-enforcement notice under K.C.C. Title 23.
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