A bioretention planter drainage assembly features a total depth of fifty inches, comprising a three-inch mulch layer, an eighteen-inch biotreatment soil mix conforming to local stormwater technical guidance, and twelve to fifteen inches of Class II permeable rock at the base. A six-inch polyvinyl chloride riser with a twelve-inch atrium grate and low-profile adapter provides overflow drainage with a six-inch tall grate and a two-inch freeboard. A storm drain bubble-up structure connects to incoming drainage, while a four-inch perforated subdrain is installed with a minimum zero point five percent slope toward the outlet. Waterproofing is specified between the planter and the adjacent building wall, surrounded by a minimum twelve-inch wide band of two-to-four-inch cobbles around the overflow inlets and bubble-up structures.
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