Section 390(1)(b) in The Calcutta Municipal Corporation Act, 1980
(b)to re-erect-(i)any building of which more than one-half of the cubical contents above the level of plinth have been pulled down, burnt or destroyed, or(ii)any building of which more than one-half of the superficial area of the external walls above the level of plinth has been pulled down, or(iii)any frame-building of which more than half of the number of posts or beams in the external walls have been pulled down;