In any event, no alteration, extension, reconstruction, or enlargement of a nonconforming structure may be made into any required yard area. In addition, any nonconforming structure which does not comply with the front, side, or rear yard requirements or lot width or maximum height in the district in which it is located, may be altered, extended, reconstructed or enlarged as provided in this section, provided said alteration, extension, reconstruction, or enlargement does not increase the front, side, or rear yard, or lot width or height nonconformity beyond its existing nonconformity.