This assembly features a primary roof drain and an adjacent overflow roof drain integrated into a single-ply thermoplastic polyolefin roofing system. The TPO membrane is adhered to the substrate using manufacturer-specified adhesive and is clamped between the drain body and the compression ring. A continuous bead of water block sealant is applied beneath the membrane at the clamping ring interface to ensure a watertight seal. The insulation adjacent to the drain is tapered to provide a slope of one inch per twelve inches toward the drain inlet. The membrane opening at the drain must extend at least one-half inch beyond the clamping ring and exceed the diameter of the leader pipe. The overflow drain is positioned with a minimum one-half inch vertical clearance above the primary roof surface to manage excess water levels.
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