A horizontal addition proposed for a building or structure that was constructed after the date specified in Section 32-202 of the County Code shall comply with the applicable requirements of Section 32-207 of the County Code and this Section. For horizontal additions, whether structurally connected or not structurally connected, to the base building: If the addition combined with other proposed repairs, alterations, or modifications of the base building constitutes substantial improvement, the base building and the addition shall comply with the applicable requirements of Section 32-207 of the County Code and this Section. If the addition constitutes substantial improvement, the base building and the addition shall comply with all of the applicable requirements of Section 32-205 of the County Code and this section. Note: The base building is required to comply otherwise it is an obstruction that does not comply with the free-of-obstruction requirement that applies to the elevated addition under Section 32-208 of the County Code. A horizontal addition to a building or structure that is not substantial improvement is not required to comply with this section.