This assembly details a duct penetration through a roof using a prefabricated insulated curb secured to the roof structure. A nailer strip is fastened to the top of the curb to receive the counter-flashing, which is secured with stainless steel sheet metal screws. The counter-flashing features welded corner seams and is installed with a minimum eight-inch vertical clearance above the finished roof. All seams, joints, and screws are waterproofed with outdoor ultraviolet-resistant sealant, and the standing seam is secured at twelve inches on center with a minimum of two fasteners per side. The base of the ductwork is sealed all around at the roof penetration point.
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