Any building, improvement or use of a building or improvement, or the use of land as a quarry, sandpit, gravel pit or top soil stripping, permitted on April 11, 1971, or the effective date of any amendment to this chapter, which would be prohibited or restricted by the terms thereof, may continue to exist until voluntarily removed or terminated, subject to the following conditions:
A. 
Alterations. A building occupied as a nonconforming use may not be reconstructed or structurally altered to enlarge the ground floor area thereof by more than 25%, unless said building is changed to a conforming use.
B. 
Garages and other structures. Garages, whether attached or detached, breezeways and patios may be constructed not in conformity with the yard requirements of this chapter on any lot lawfully occupied and used for residential purposes prior to April 11, 1971, after waiver granted by the Board of Appeals. Such waiver shall be granted only so that substantial justice shall be done, the spirit of this chapter adhered to and upon such terms and conditions as the Board of Appeals shall determine.
C. 
Extension. A nonconforming use shall not be extended, but the extension of a conforming use to any portion of a nonconforming building which existed prior to April 11, 1971 shall not be deemed an extension of such nonconforming use.
D. 
Construction. Nothing contained herein 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 the issuance of such permit.
E. 
Cessation. Whenever a nonconforming use has ceased for a period of one year, it shall not thereafter be reestablished, and any future use shall be in conformity with the provisions of this chapter.
F. 
Changes. Once changed to a conforming use, no building or land shall be permitted to revert to a nonconforming use.
G. 
District changes. Whenever the boundaries of a district shall be changed to transfer an area from one district to another district, the provisions of this section shall apply to any nonconforming uses created thereby.
H. 
Compliance with § 150-47. Notwithstanding that the use of land as a quarry, sandpit, gravel pit or for top soil stripping shall be entitled to status as a nonconforming use under the provisions of this section, no such use shall continue after the effective date of this chapter, except upon compliance with the provisions of § 150-47.