A lawful preexisting nonconforming structure may be altered, reconstructed, enlarged and/or expanded, including an extension of a nonconforming building footprint, so long as the alteration, reconstruction, enlargement and/or expansion does not create a new dimensional nonconformity or worsen an existing dimensional nonconformity without the granting of a variance. In the case of a nonconforming structure which is used by a nonconforming use, any expansion shall also meet the requirements for nonconforming uses as set forth in this chapter.