Any combination of reconstruction, alteration, or improvement to a building, taking place (pick during the life of the building or a given year period), in which the cumulative percentage of improvement equals or exceeds fifty percent of the current market value of the building. For the purposes of this definition, an improvement occurs when the first alteration of any wall, ceiling, floor, or other structural part of the building commences, whether or not that alteration affects the external dimensions of the building. This term includes structures, which have incurred “repetitive loss” or “substantial damage”, regardless of the actual repair work done. The term does not apply to: (1) any project for improvementof a building required to comply with existing health, sanitary, or safety code specifications which have been identified by the Code Enforcement Official and which are solely necessary to assure safe living conditions, or (2) Any alteration of an “historic structure” provided that the alteration will not preclude the structure’s continued designation as a “historic structure”. Or (3) Any building that has been damaged from any source or is categorized as repetitive loss. Substantially improved existing manufactured home parks or subdivisions is where the repair, reconstruction, rehabilitation or improvement of the streets, utilities and pads equals or exceeds 50 percent of the value of the streets, utilities and pads before the repair, reconstruction or improvement commenced