Section 31(2)(b) in West Bengal Municipal (Building) Rules, 2007
(b)if during the erection or execution of work any external deviation beyond the sanctioned covered space, either horizontal or vertical or both, is intended to be made and which does not violate the provisions of the Act or these rules, the person referred to sub-rule (1) of rule 11 shall, prior to carrying out such erection or execution of works, submit, in accordance with the provisions of these rules, a revised plan incorporating the deviations intended to be carried out, for obtaining necessary sanction therefor;