The lawful use of any building or land existing at the time of the enactment of this chapter may be continued although such use does not conform with the provisions of this chapter.

A nonconforming use or a use nonconforming as to its bulk shall not be extended. Nothing herein contained shall prohibit the construction of accessory uses or uses deemed minor in accordance with § 210-77D of this chapter. In such cases, construction of accessory uses shall not be considered to be an extension.

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 nine months of the date of the permit and which entire building shall be completed according to such plans as filed within one year from date of this chapter.

Any building or structure damaged by fire or other accidental and unintentional causes to any extent of its assessed value shall, when repaired or rebuilt, be in conformity with the regulations of this chapter as much as possible, without such conformity causing undue hardship to the owner. Any demolished building or structure shall, when repaired or rebuilt, be in conformity with this chapter.

Whenever a nonconforming use has been discontinued for a period of one year, such use shall not thereafter be reestablished, and any future use shall be in conformity with the provisions of this chapter.

Once changed to a conforming use, no building or land shall be permitted to revert to a nonconforming use. A nonconforming use may be changed to a use of the same or higher classification, subject to the provisions of § 210-93 and §§ 210-70 through 210-80, and such use thereafter shall not be changed to a lower classification.

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.