Section 118(3)(c) in West Bengal Municipal (Building) Rules, 2007
(c)ventilation ducts, provided such ducts have 1.30 cm2 of area for each m2 (2 in2 of area for each ft2) of floor area with a minimum total area of 330 m2 (48 in2) and a least dimension of 9 cm (31/2 in). The vent register or grills to the duct shall be located in or next to the ceiling or the ventilated space. A separate duct from each space or room shall run to and above the roof and shall be provided with a lowered vent stack :