(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.