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If a horizontal branch connects to the stack within 2 feet (610 mm) above or below a vertical stack offset, and the offset is located more than four branch intervals below the top of the stack, the offset shall be vented in accordance with Section 18-29-915.
Vents for vertical offsets required by Section 18-29-711.1 shall not be required where the stack and its offset are sized as a building drain (see Table 18-29-710A, Column 5).
A stack with a horizontal offset located more than four branch intervals below the top of the stack shall be vented in accordance with Section 914 and sized as follows:
1. The portion of the stack above the offset shall be sized as for a vertical stack based on the total number of drainage fixture units above the offset.
2. The offset shall be sized in accordance with Section 18-29-710.1.1.
3. The portion of the stack below the offset shall be sized as for the offset or based on the total number of drainage fixture units on the entire stack, whichever is larger (see Table 18-29-710B, Column 4).
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.
Drainage stacks that receive wastes from sinks, automatic dishwashers, laundry trays, laundry washing machines, and similar fixtures shall have the drainage and vent piping so arranged that suds pressures will not affect fixtures in the lower portion of the drainage system. No fixture drain, branch, or branch vent shall connect to any stack in a suds pressure zone. Such zones shall be considered to exist at any offset of 60 degrees to 90 degrees or at the base of any drainage.
When the drainage portion of a stack exceeds 16 feet (4.88 m) in height above a 45-degree to 90-degree offset or house drain, it shall have its lower portion consisting of 30 percent of its height from such offset free of any fixture drain or branch. Such suds pressure zone of the drainage stack need not exceed 24 feet (7.32 m) in height.
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