Except as otherwise provided in this article, the lawful use of land or buildings 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:

A nonconforming use shall be adjudged abandoned when there occurs a cessation of any such use or activity by an apparent act or failure to act on the part of the tenant or owner to reinstate such use within a period of one year from the date of cessation or discontinuance. Such use shall not thereafter be reinstated and the structure shall not be reoccupied, except in conformance with this chapter.

Nothing herein contained shall require any change in plans, construction or designated use of a building for which a building permit has been heretofore 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 which entire building shall be completed according to plans as filed within one year from the date of this chapter.

No nonconforming use shall, if once changed into a conforming use, be changed back to a nonconforming use.

A nonconforming building may be altered, but not enlarged or extended, during its life to an extent not exceeding in aggregate 50% of the recorded true value as appraised in the records of the Tax Assessor of the building, unless said building is changed to a building conforming to the requirements of this chapter.

If any nonconforming building shall be destroyed by reason of windstorm, fire, explosion or other act of God or the public enemy to an extent of more than 75% of the recorded true value, as appraised in the records of the Tax Assessor, then such destruction shall be deemed complete destruction, and the structure may not be rebuilt, restored or repaired except in conformity with the regulations of this chapter. Nothing in this chapter shall prevent the strengthening or restoring to a safe condition of any wall, floor or roof which has been declared unsafe by the Zoning Inspector.

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 also apply to any nonconforming uses existing therein or created thereby.