The Ontario Building Code | Size Restriction
22.214.171.124. Size Restriction
(2) Every sanitary building drain shall terminate at its upstream end in a stack of at least 3 in. size.
(3) A stack referred to in Sentence (2) shall be a soil stack if one is available and may be a vent stackor waste stack that provides at least 3 in. stack vent and that goes to open airabove the roof, either directly or through a header.