MarkhamBuilding InspectionsInspections

Protection From Backflow

Published by City of Markham

This is the City of Markham’s document, as published on its website on 18 October 2026. The municipality may have changed it since: check the current version at the source. Legal notice

Type: Guide
Published by: City of Markham
Date: January 1, 2025
Also called: Protection from Backflow
For: builder
Building types: All building types
Pages: 3
Instruments: CAN/CSA-B70 · CAN/CSA-B181.1 · CAN/CSA-B181.2 · CAN/CSA-B182.1

Overview

Markham's Builder Tip No. 108, dated January 1, 2025 and updated to the 2024 OBC, on backwater valves in houses of up to two dwelling units, filed with the City's housing tips under the 2024 Ontario Building Code. It quotes the Building Code Act roles of chief building officials and builders and Article 7.4.6.4., Protection from Backflow, with normally open valves to CAN/CSA-B70, B181.1, B181.2 or B182.1. A section headed When Are Backwater Valves Required? names flood prone zones, and diagrams show main drain and branch drain valves.

What it covers

Building Code Act
Role of chief building officials
Role of builders
Ontario Building Code
7.4.6.4. Protection from Backflow
Objective of this Builders Tip
When Are Backwater Valves Required?
Main Drain Backwater Valve
Branch Drain Backwater Valves - Multi Dwelling

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