Section 95(19)(c) in West Bengal Municipal (Building) Rules, 2007
(c)teak and other hard woods when used for beams and posts or in combination with iron, the timber and iron being protected by a plastering or coating with an incombustible and non-conducting external coating not less than 6 cm (or 2 inch) thick, or, in the case of timber, not less than 2.5 cm. (or 1 inch) thick;