Any building or structure or any use of a building or structure or premises or part thereof lawfully existing at the time this bylaw or any amendment thereto is adopted may be continued although such building or structure or use does not conform to the provisions thereof. This article shall not apply to nor grant any exemption to any billboards, signs or other advertising devices subject to MGL c. 93, §§ 29 to 33 and MGL c. 93D.

Any lawful building or structure or use of a building or structure or premises or part thereof at the time this bylaw or any amendment thereto is adopted may be extended or altered, provided that no such extension or alteration shall be permitted unless there is a finding by the Board of Zoning Appeals that such change, extension or alteration shall not be substantially more detrimental than the existing nonconforming use to the neighborhood, subject to the conditions and requirements of Article XXV of this bylaw.

No building or structure which has been damaged by fire or other causes to the extent of more than 3/4 of its value shall be repaired or rebuilt except in conformity with this bylaw, unless the Board of Zoning Appeals finds that the restoration is for the same use and that the building or structure is not substantially greater in area, height or size and not nearer to adjoining lots, subject to the conditions and requirements of Article XXV of this bylaw.

If the nonconforming use of any building or structure shall be abandoned or shall be discontinued for a period of 24 consecutive months, it shall not be reestablished, and all future use thereof shall be in conformity with the applicable provisions of this bylaw, unless prior to the expiration of the 24 months permission to reestablish said use has been applied for and thereafter granted by special permit from the Board of Zoning Appeals.

It is hereby provided that construction or operations under a building permit or special permit shall conform to any subsequent amendment of this bylaw unless the use or construction is commenced within a period of not less than six months after the issuance of the permit and, in cases involving construction, unless such construction is continued through to completion as continuously and expeditiously as is reasonable.