An exhaust fan mounts to a prefabricated and insulated attenuating curb positioned twelve inches minimum above the finished roof surface. Flashing and counter flashing are provided by the general contractor, while the duct is secured directly to the curb with screws. The roof penetration is sealed with flexible waterproof mastic around the sheet metal duct. A backdraft damper is integrated into the ductwork below the roof line where noted on the schedule.
SHEET METAL DUCT SEAL ROOF PENETRATION WITH FLEXIBLE WATERPROOF MASTIC SCREW DUCT TO CURB FLASHING AND COUNTER FLASHING BY GENERAL CONTRACTOR WHERE NOTED ON SCHEDULE, PROVIDE ATTENUATING CURB 12" MINIMUM ABOVE FINISHED ROOF PREFABRICATED AND INSULATED CURBY BY MECHANICAL CONTRACTOR EXHAUST FAN BACKDRAFT DAMPER
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