Enlargement — Repair — Alterations. Any non-conforming structure may be enlarged, maintained, repaired or remodeled; provided, however, that no such enlargement, maintenance, repair or remodeling shall either create any additional non-conformity or increase the degree of existing non-conformity of all or any part of such structure. Notwithstanding the above, a porch which is covered by a roof which extends into the front setback area may be enclosed, but not in excess of the area covered by the existing roof.