Section 26(2)(b) in Kolkata Municipal Corporation Building Rules, 2009
(b)if during the erection or execution of the work, any external deviation beyond the sanctioned covered space is intended to be made and which does not violate the provisions of the Act or these rules, the person referred to in sub-rule (1) of rule 4, 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 deviation intended to be carried out, for obtaining necessary sanction.