Exhaust Duct Clearance
Adequate clearance to combustible building members is critical, if cooking produces concentrations of grease-laden vapors. Clearance from the exhaust duct to the interior surface of unprotected combustible building members should not be less than 18” (inches).
Clearances may be reduced when combustible material is protected as follows:
0.013-inch (#28 gage) sheet metal spaced out 1-inch on non-combustible spacers = 9 inch clearance
0.027-inch (#22 gage) sheet metal on 1-inch mineral wool bats reinforced with wire mesh or equivalent spaced out 1-inch on noncombustible spacers = 3 inch clearance
Materials and products listed for the purpose of reducing clearance to combustibles must be installed in accordance with the condition of the listing and the manufacturer’s instruction.
Noncombustible Exhaust Duct Enclosure
Cooking exhaust ducts should be enclosed in a continuous enclosure extending from the ceiling, above the hood, through any concealed space, to or through the roof.
This enclosure should conform to the following:
• Buildings less than 4 stories in height, should have a fire resistive rated enclosure of not less than 1 hour.
• Buildings 4 stories or more, should have a fire resistive rated enclosure of not less than 2 hours.
Exhaust Duct Connections
Exhaust ducts should lead, as directly as possible, to the exterior of the building. They should not pass through fire walls or fire partitions. Ducts should not be interconnected with any other ventilating or exhaust system within the building.
Fire Protection For Cooking Equipment
UL Listed fixed automatic extinguishing protection should be provided for the hood, exhaust ducts and cooking surfaces. (Refer to Loss Control Data Guide F.13344 for complete details).