A ventilation fan sits atop a prefabricated roof curb secured to the roof assembly with number eight sheet metal screws at twenty-four inches on center maximum with three each side minimum typically. Counter flashing extends down over a cant strip and is anchored to the blocking with three-eighths inch diameter expansion anchors at twenty-four inches on center maximum with three anchors on each side minimum. A backdraft damper is installed within the duct as required below the roof penetration. Notes specify securing the hood to wood using three-eighths inch cadmium plated lag bolts not over twenty-four inches on center, and anchoring the curb, ductwork, and damper with expansion bolts for concrete roofs or rust-resistant bolts for metal deck and joist roofs.
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