Section 2(20)(b) in The Howrah Municipal Corporation Act, 1980
(b)any building which, having collapsed or having been demolished or burnt down for more than one-half of its cubical extent of the space contained within the external surface of its walls and roof and the upper surface of the floor of its lowest or only storey, is reconstructed wholly or partially after the commencement of this Act, whether the dimensions of the reconstructed building are the same as those of the original building or not,