In all districts, if any building, except a building subject to the provisions of Section 52-54 (Buildings Designed for Residential Use in Residence Districts), or of Section 52-56 (Multiple Dwellings in M1-1D Through M1-5D Districts), which is substantially occupied by a non-conforming use, is damaged or destroyed by any means, including any demolition as set forth in Sections 52-50 et seq., to the extent of 50 percent or more of its total floor area, such building may either:

(a)        be repaired or incidentally altered, and the existing non-conforming use may be continued; or

(b)        be reconstructed, but only for a conforming use; provided, however, that in no event shall any such reconstruction create a non-compliance or increase the degree of non-compliance of a non-complying building.

However, where the damage or destruction is so great that the provisions in Sections 54-41 and 54-42 relating to Damage, Destruction or Demolition in Non-Complying Buildings also apply, the latter Sections shall govern the permitted bulk of the reconstructed building.

In addition, the alteration of an existing building resulting in both the removal of more than 75 percent of the floor area and more than 25 percent of the perimeter walls of such existing building, and the replacement of any portion thereof, shall be considered a development for the purposes of the provisions set forth in Section 11-23 (Demolition and Replacement).

In applying the provisions of this Section to damaged or destroyed structures, substantially utilized by a non-conforming use, any appropriate measure of the size of such structures shall be substituted for floor area in determining the extent of damage or destruction.

In the event that any demolition, damage or destruction of an existing building produces an unsafe condition requiring a Department of Buildings order or permit for further demolition of floor area to remove or rectify the unsafe condition, and the aggregate floor area demolished, damaged or destroyed including that ordered or permitted by the Department of Buildings constitutes 50 percent or more of the total floor area of such building, then such building may be repaired or reconstructed only in accordance with the provisions of paragraph (a) or (b) in this Section.

For the purposes of this Section, any single-family or two-family residence located within an M1-1D, M1-2D, M1-3D, M1-4D, M1-5D or M1-6D District and existing on June 20, 1988, shall be a conforming use.

For the purposes of this Section, buildings that abutted one another on a single zoning lot on the date of such damage or destruction shall be considered a single building.