The structural alterations made in such building shall in no case exceed 20% of the true value of the buildings, nor shall the building be enlarged, unless the use therein is changed to a conforming use; provided, however, that where a building meets the use requirements of this chapter and is nonconforming because of height and area regulations, structural alterations may be made in such buildings, provided that the height and area regulations are not further violated.

A nonconforming use changed to a conforming use may not be changed back to a nonconforming use.

In the event that there is a cessation of operation of any nonconforming use, structure, land or sign for a period of 12 consecutive calendar months, the same shall be presumed to be an abandonment of such nonconforming use. Any subsequent exercise of such abandoned nonconforming use shall be deemed a violation of the terms of this chapter.

Nothing in this chapter shall require any change in plans, construction or designated use of a structure for which a building permit has been heretofore issued when construction has been diligently prosecuted within six months of the date of such permit.

Nothing in this chapter shall be interpreted as authorization for or approval of the continuance of the use of a structure or premises in violation of zoning regulations in effect at the time of the effective date of this chapter.

No nonconforming use shall be reduced in size. An owner of two or more contiguous nonconforming lots at the time of the effective date of this chapter which, when combined, would create a lot of conforming size shall be required to combine such lots to create conforming lots.

Any nonconforming building existing at the time of the passage of this chapter may be restored or repaired in the event of partial destruction thereof by fire, explosion, act of God or act of public enemy. However, any building which is substantially destroyed in the manner aforesaid may be reconstructed and thereafter used only in such a manner as to conform to all provisions of this chapter or pursuant to such variances as may be granted by the Board of Adjustment. When the Zoning Officer has denied a permit for restoration of any such building pursuant to this chapter, he or she shall forthwith refer the application to the Board of Adjustment. In determining whether or not destruction has been partial, the Board of Adjustment shall be guided by the facts and circumstances of the application being considered, giving due regard to, but without being limited to, the following factors.

When setting forth its conclusions under this section, the Board of Adjustment shall make specific factual findings upon which its decision is based. Nothing in this section shall prevent the restoration of a wall declared unsafe by the Building Inspector.