A nonconforming use of a building or land may be extended up to 25% of the area occupied by such use at the effective date of this chapter, June 25, 1979, when authorized by the Zoning Board of Adjustment. Any such extension or enlargements shall be immediately adjacent to the existing nonconforming use, shall be located on the lot held in a single and separate ownership on June 25, 1979, and shall conform to the area and height regulations of the district in which it is situated.