7.4.6.4.Protection from Backflow (See Note A-7.4.6.4.)

(1) Except as permitted in Sentence (2), a backwater valve that would prevent free circulation of air shall not be installed in a building drain or in a building sewer. (2) A backwater valve may be installed in a building drain provided that, (a) it is a “normally open” design conforming to, (i) CAN/CSA-B70, “Cast Iron Soil Pipe, Fittings, and Means of Joining”, (ii) CAN/CSA-B181.1, “Acrylonitrile-Butadiene-Styrene (ABS) Drain, Waste, and Vent Pipe and Pipe Fittings”, (iii) CAN/CSA-B181.2, “Polyvinylchloride (PVC) and Chlorinated Polyvinylchloride (CPVC) Drain, Waste, and Vent Pipe and Pipe Fittings”, or (iv) CAN/CSA-B182.1, “Plastic Drain and Sewer Pipe and Pipe Fittings”, and (b) it does not serve more than one dwelling unit. (3) Except as provided in Sentences (4) and (5), where a building drain or a branch may be subject to backflow, (a) a backwater valve shall be installed on every fixture drain connected to it when the fixture is located below the level of the adjoining street, or (b) a backwater valve shall be installed to protect fixtures which are below the upstream sanitary manhole cover when a residential building is served by a public sanitary sewer. (4) Where more than one fixture is located on a storey and all are connected to the same branch, the backwater valve may be installed on the branch. (5) A subsoil drainage pipe that drains into a sanitary drainage system that is subject to surcharge shall be connected in such a manner that sewage cannot back up into the subsoil drainage pipe.