The exhaust fan is mounted atop a prefabricated and insulated curb, which maintains a minimum height of 12 inches above the finished roof surface. The sheet metal duct is secured to the interior of the curb with screws. A backdraft damper is installed within the duct penetration. The roof penetration is sealed with a flexible waterproof mastic, and the curb is finished with flashing and counter-flashing provided by the general contractor.
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