Canadian Underwriter

Guidance should be to interpret codes as requiring installation of backwater valves

February 15, 2013   by Canadian Underwriter

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Guidance on how language within building and plumbing codes should be interpreted with respect to backwater valves should support mandatory installation in all or most new Canadian homes, suggests a research paper released today by the Institute for Catastrophic Loss Reduction (ICLR).


The paper recommends rewording or clarifying sentences in the National Plumbing Code and other provincial building and/or plumbing codes relating to installation of backwater valves to protect homes from sewer backflow to ensure they are clearly and consistently interpreted and applied.

As an alternative to changing wording, provincial and national code authorities should “provide guidance to local authorities about how code wordings related to protection of homes from sewer backflow should be interpreted. This guidance should outline that code wordings be interpreted in a way that requires the mandatory installation of backwater valves in all or most new Canadian homes,” notes the study abstract of Urban flooding in Canada: Lot-side risk reduction through voluntary retrofit programs, code interpretation and by-laws.

The paper, available for download at, was written by Dan Sandink, ICLR’s manager of resilient communities and research.

“Due to the unpredictable nature of extreme rainfall events and the unpredictability of infiltration and inflow (I/I) in relatively new, separated sewer systems, it is often impossible to identify which regions of an urban municipality are exposed to sewer backup risk until widespread or regional sewer backup events have occurred,” the abstract notes. “It is also more economical to install backwater valves in new homes when compared to retrofitting valves into existing homes,” it adds.

Mandatory requirement is justified because of the “substantial costs associated with sewer backup insurance claims, the legal liability of municipalities generated by regional sewer backup events, health and home liveability risks posed to households created by sewage flooding and the fact that urban flooding and sewer backup occurrences are likely to increase as a result of increasing frequency of extreme rainfall caused by climate change,” notes the abstract.

Sewer backup is a significant cause of basement flooding associated with extreme precipitation events and urban flooding.

ICLR reports that urban flood damages are a recurrent and growing issue for municipalities, with damages often totalling in the tens and hundreds of millions of dollars. The institute cites the following examples:

  • $260 million in insured damages following the May 2012 storm system that affected Thunder Bay before moving through to Montréal;
  • $90 million in insured damages in the wake of a July 2012 storm that moved through southern Ontario, affecting several neighbourhoods in Hamilton and Ottawa;
  • more than $500 million in insured damages as a result of an extreme rainfall event in August 2005 that affected a stretch of southern Ontario from Hamilton to Durham Region ($247 million of which was associated with sewer backup);
  • $300 million in insured damages in southern Alberta in 2005 following heavy rainfall and associated flooding; and
  • approximately $166 million in insured damages ($143 million associated with sewer backup) as a result of a severe storm in Edmonton in 2004.

“Despite consistent application of code wordings related to backwater valves across the regions of Canada represented in this study, it was found that there are differing interpretations of code wordings, which resulted in differing reported frequencies of installation of backwater valves on both sanitary/combined and storm sewer service connections,” the paper notes.

It explores, among other topics, interpretation of building and plumbing code wording related to the installation of backwater valves designed to protect homes from sewer backup. “While a significant amount of research by ICLR and others has concluded that resolution of building code enforcement issues may result in reduced vulnerability to extreme natural hazards, issues surrounding code interpretation have not previously been studied,” notes the ICLR statement.

“Despite the fact that the National Building Code of Canada and virtually all provinces use near identical code wordings in the backwater valve sections of their respective building and/or plumbing codes, this study found that there are differing interpretations of code wordings, resulting in differing frequencies of installation of backwater valves,” Sandink notes.

Building and plumbing officials in many jurisdictions across the country interpret the code as meaning that all new homes should have the valves, while the interpretation of some officials in some jurisdictions is that the valves are to be used only in certain circumstances.

“Requiring installation of valves in new homes would also help offset relatively low uptake frequencies for municipal subsidy programs aimed at encouraging homeowners to adopt urban flood risk reduction measures.”