Nonconforming building or use. Any lawful nonconforming use of a portion of a building may be extended throughout the building, and 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 the ordinance which rendered the property nonconforming, provided that the increase in horizontal cross-section area of the building, or portion of building, shall not be in excess of 30% of the horizontal cross-section area of the building on the lot existing on the date it became lawfully nonconforming and provided, further, that any extension shall conform to all height, area, width, yard, building coverage, impervious material coverage, green area coverage and landscaping and screening requirements for the zoning district in which it is located and the off-street parking requirements for the specific use.