Offsets in
multistory common vent systems shall be limited to a
single offset in each system, and systems with an offset
shall comply with the following:
- The offset angle shall not exceed 45 degrees (0.79 rad) from vertical.
- The horizontal length of the offset shall not exceed 18 inches per inch (18 mm/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 x maximum common vent capacity).
- A multistory common vent shall not be reduced in size above the offset. [NFPA 54:13.2.17]