Extension. The lawful nonconforming use of a lot, building or a portion of a building shall not be increased or enlarged unless the Zoning Hearing Board shall, as a special exception, authorize such increase. The area devoted to a nonconforming use within a building shall in no case be increased or enlarged by more than a total of 25% of the area used for the use as of the time the use first became nonconforming. Any lawful nonconforming building or any building of which a lawful nonconforming use is made may be extended upon the lot occupied by such building and held in single and separate ownership on the effective date of this chapter, provided that the area of such building shall not be increased by more than a total of 50% of the area of such building existing on the date it first became a lawful nonconforming building, or a building in which a lawful nonconforming use is made and provided further that any structure alteration, extension or addition shall confirm with all height, area, width, yard and coverage requirements for the District in which it is located. In the event a part of a lot shall be used for a lawful nonconforming use, whether in a building or otherwise, the area occupied by such nonconforming use shall not be increased by more than a total of 50% of the area of the lot used upon the effective date of this chapter.