506.3.6 Grease duct clearances.
MC § 506.3.6
Where enclosures are not required, grease duct systems and exhaust equipment serving a Type I hood shall have a clearance to combustible construction of not less than 18 inches (457.2 mm), and shall have a clearance to noncombustible construction and gypsum wallboard attached to noncombustible structures of not less than 3 inches (76.2 mm). Exceptions: 1. For factory-built commercial kitchen grease ducts listed and labeled in accordance with UL 1978, the required clearance shall be in accordance with the listing of such material and as approved by the commissioner.
2.Listed and labeled exhaust equipment installed in accordance with Section 304.1.
3.Where commercial kitchen grease ducts are continuously covered on all sides with a listed and labeled field-applied grease duct enclosure material, system, product or method of construction specifically evaluated for such purpose in accordance with ASTM E 2336, the required clearance shall be in accordance with the listing of such material, system, product or method.
4.Grease ducts protected with a minimum insulation covering of 2 inches (50.8 mm) of magnesium or calcium silicate block, with staggered joints, attached with galvanized steel wire or material assembly equivalent in insulating and fire-resistant qualities which cannot be penetrated by grease. Such protection shall be applied to all ducts inside of the building as approved by the commissioner.
