Offsets in multistory common vent systems shall be limited to a single offset in each system, and systems with an offset shall comply with all of the following:
- The offset angle shall not exceed 45 degrees (0.79 rad) from vertical.
- The horizontal length of the offset shall not exceed 11/2 feet for each inch (18 mm for each 25.4 mm) of common vent diameter of the segment in which the offset is located.
- For the segment of the common vertical vent containing the offset, the common vent capacity listed in the common venting tables shall be reduced by 20 percent (0.80 × maximum common vent capacity).
- A multistory common vent shall not be reduced in size above the offset.