In Commercial Districts mapped within, or with a residential equivalent of an R1 through R5 district, for the purposes of applying the provisions of Section 23-42 (Height and Setback Requirements in R1 Through R5 Districts), inclusive, to qualifying residential sites, the applicable Residence District regulations shall apply, including as modified by the provisions of Section 35-22. 

However, for the purposes of applying the provisions of Section 23-423 (Standard setback regulations), for building street walls fronting a street where a Commercial District is mapped along the entire block frontage, for the portion of such street wall that exceeds the maximum base height, a setback shall be provided at a height not lower than a minimum base height of 20 feet and not higher than the maximum base height set forth in Section 23-424 (Height and setback requirements for qualifying residential sites).

Additional height and setback provisions are set forth in Section 35-64, inclusive.

The height of all buildings or other structures shall be measured from the base plane. For the purposes of this Section, where base planes of different elevations apply to different portions of a building or other structure, each such portion of the building may be considered to be a separate building.