Air from exhaust ducts with grease shall be vertical exhaust outlets for grease ducts serving commercial food heat-processing equipment shall extend vertically through the roof. Such extentions shall be at least ____ above the roof surface.

Air from exhaust ducts with grease shall be vertical exhaust outlets for grease ducts serving commercial food heat-processing equipment shall extend vertically through the roof. Such extentions shall be at least ____ above the roof surface.