Vents for horizontal stack offsets required by Section 18-29-711.3 shall not be required where the stack and its offset is one pipe size larger than required for a building drain (see Table 18-29-710A, Column 5) and the entire stack and offset is not less in cross- sectional area than that required for a straight stack plus the area of an offset vent as provided for in Section 18-29-915. Omission of offset vents in accordance with this section shall not constitute approval of horizontal branch connections within the offset or within 2 feet (610 mm) above or below the offset.