The Ontario Building Code | Protection from Backflow

7.4.6.4. Protection from backflow

(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 branchmay be subject to backflow,

(a) a backwater valve shall be installed on every fixture drainconnected to it when the fixture is located below the level of the adjoining street, or

(b) a backwater valve shall be installed to protect fixtureswhich 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 valvemay 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 sewagecannot back up into the subsoil drainage pipe.