Except as otherwise provided in this article, the otherwise lawful use of land or a building existing at the date of the adoption of this chapter may be continued although such use or building does not conform to the regulations specified by this chapter for the zone in which such land or building is located; provided, however, that no nonconforming lot shall be further reduced in size.

No building damaged by fire or other causes shall be repaired or rebuilt so as to extend or enlarge the nonconforming use to which it was devoted at adoption of this chapter. Buildings totally destroyed by fire or other causes, or demolished by the owner, shall not be rebuilt except in conformity with the regulations of this chapter. Nothing in this chapter shall prevent the strengthening or restoring to a safe condition any wall, floor or roof which has been declared unsafe by the Building Inspector.

If a nonconforming building or use is subsequently changed to conforming use, it shall not again be constructed, altered, occupied or used except in conformity with the requirements of the district wherein such building or use is located.

A nonconforming building may be constructed or structurally altered to an extent not greater than 25% of the square footage of the building as existing on the effective date of this chapter, provided that no nonconforming use is extended or changed to another nonconforming use, and provided that this section shall not permit construction or alteration which would be prohibited by § 270-128.

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

Nothing herein contained shall require any change in plans, construction or designated use of a building, structure or sign for which a building permit has heretofore been issued and the construction of which shall have been diligently prosecuted within three months of the date of such permit, and the ground story framework of which, including the second tier of beams, shall have been completed within six months of the date of the permit, and where the entire building shall have been completed according to such plans as filed within one year from the date of the adoption of this chapter.