The Ontario Building Code | Offset Relief Vents
220.127.116.11. Offset Relief vents
(1) A soil or waste stack that has a nominally horizontal offset more than 1 500 mm long and above which the upper vertical portion of the stack passes through more than 2 storeys and receives a hydraulic load of more than 100 fixture units shall be vented by an offset relief vent connected to the vertical section immediately above the offset, and by another offset relief vent,
(b) extended as a vertical continuation of the lower section.