In R6 through R10 Districts without a letter suffix, on zoning lots where demolition or disposition is subject to approval from the U.S. Department of Housing and Urban Development (HUD) under section 18 of the Housing Act of 1937, the provisions of this Section shall apply.

For developments or enlargements of residences other than qualifying senior housing or MIH developments on MIH sites:

1. on zoning lots where the height of any existing building containing residences exceeds the heights for zoning lots containing standard residences set forth in Section 23-432, the regulations for sky exposure plane buildings set forth in Section 23-73, inclusive, shall apply, and shall not be optional; and
2. on zoning lots where the height of all existing building containing residences are less than or equal to the heights for zoning lots containing standard residences set forth in Section 23-432, the bulk regulations for residential buildings of this Chapter applicable to non-sky exposure plane buildings may be applied, except that:
   1. the height and setback modifications for eligible sites set forth in Section 23-434 shall not apply; and 
   2. the minimum distance between buildings two of more buildings on the same zoning lot that are not connected at any level shall be governed by the provisions of paragraph (c) of Section 23-735. Notwithstanding the provisions of Section 23-05, the use of this Section shall not necessitate the utilization of all other provisions for sky exposure plane buildings unless other provisions of Section 23-73, inclusive, are applied.