In all Residence Districts, if the floor area occupied by non-conforming uses within a building designed for residential use is damaged or destroyed by any means, including but not limited to, any demolition ordered or permitted by the Department of Buildings, to the extent of 25 percent or more of such floor area, such building may be continued in use or reconstructed only in accordance with the provisions of Section 52-53 (Buildings or Other Structures in All Districts) except that the 25 percent ratio set forth in this Section shall apply instead of the 50 percent ratio set forth in Section 52-53.