The extension or enlargement shall conform to the height, area, yard and impervious coverage regulations of the district in which it is located. Where a building, structure or use is nonconforming as to a required side yard or rear yard setback, the established nonconforming setback may be continued, so long as the proposed extension or enlargement does not project further into any yard, whether a front, side or rear yard, than the original setback line extended. Extension or enlargement of the nonconforming use, building or structure shall not exceed 50% of the floor area or use existing on the effective date of this chapter or the date of an amendment thereto thereby creating the nonconformity.