Subject to the provisions of this article, a use of a building or land existing at the time of the enactment of this chapter, may be continued even though such use does not conform with the provisions of these regulations for the district in which it is located.

Nothing in this chapter shall prevent the strengthening or restoring to a safe condition of any portion of a building or structure declared unsafe by a proper authority.

A nonconforming building or structure may be altered, improved or reconstructed, provided that such work is not to an extent exceeding, in aggregate cost, 50% of the fair market value of the building or structure, unless the building or structure is changed to a conforming use.

Nothing in this chapter shall prevent the reconstruction, repairing, rebuilding and continued use of any nonconforming building or structure which is damaged by fire, collapse, explosion or act of God subsequent to the date of this chapter, wherein the expense of such work does not exceed 50% of the fair market value of the building or structure at the time such damage occurred.

A nonconforming use shall not be extended to exceed the yard, lot or area requirements set forth for its particular district.

No nonconforming building, structure or use shall be changed to another nonconforming use.

Nothing herein contained shall require any change in plans, construction or designated use of a building or structure for which a building permit has been issued and the construction of which shall have been diligently pursued within two months of the date of such permit and the ground framework of which shall have been completed within four months of the date of the permit and which entire building shall have been completed according to such plans as filed within one year from the date of this chapter.

A nonconforming use of a building or land which has been abandoned shall not thereafter be returned to such nonconforming use. A nonconforming use shall be considered abandoned as follows:

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.

Whenever the boundaries of a district shall be changed so as to transfer an area from one district to another district of a different classification, the foregoing provisions shall apply to any nonconforming uses existing therein.