Mandatory Backwater Valves in All New Homes

Taking a proactive approach to the risks posed by sewer backup flooding, in 2013 the Town of Collingwood, Ontario, legislated that all new homes must be constructed with a backwater valve. In the event of a heavy rainfall, it is often the case that the municipal sewer system will be unable to handle the rapid influx of water. In this situation, the excess water will have no place to go but up through the sanitary sewer laterals, backing up raw sewage into homes. This is not a small issue, with an estimated $2 billion in damages caused by sewer backup flooding every year in Canada. A backflow valve is essentially a simple one-way gate that allows household sewage to flow out into the sanitary sewer but prevents sewage from travelling back into the home. These devices are relatively cheap, costing around $250 on average and can be installed for very little additional costs during the home construction phase.

Understanding and Assessing Impacts

Climate change is expected to significantly increase the frequency and severity of extreme rainfall across Canada. Sewer backup flooding occurs when a sewer system is inundated with more water than it has the capacity to handle. When this happens, it is possible for the excess water to be forced back up the sewer lateral and into homes. This problem is exacerbated by the high degree of impermeable surfaces in urban areas, as well as high levels of inflow and infiltration into the sewer systems by broken sewer pipes and poorly-sealed connections. Both combined and separated systems are vulnerable to this type of event. Sewer backflow valves are a cheap and easily installed during the construction phase of home development. These devices all for household wastewater to flow out into the sewer network, but prevent backflow from said network from entering the home in the event of flooding. At the time of writing, the provincial building code required backup valves in new homes only “where a building drain or a branch may be subject to backflow”. The unclear and non-specific wording of the legislation is problematic. Some jurisdictions would apply these conditions only if an existing history of flooding is present, but recent research has indicated that all homes connected to public underground sanitary sewer systems have the potential to experience sewer back up.

Identifying Actions

The impetus for this decision came from Collingwood’s Director of Building Services participation in an ICLR study on the subject of how municipal officials interpreted the building code provision concerning backwater valves in new houses. After having contributed to the study and learning about the increasing danger of backup flooding due to climate change’s effect on precipitation patterns, the Director consulted with homebuilders on the risk of backup flooding and, in January of 2013, released a public statement that all new homes in the Collingwood area must have backwater valves. Collingwood is not alone in putting forth this kind of legislation, what makes this case special is that where most other jurisdictions took action only after a damaging flood, Collingwood’s decision was proactive and taken in anticipation of the hazards of a warmer and wetter climate. Another interesting thing to note is that Collingwood chose not to alter the existing bylaws, but rather took the approach to make a public statement regarding their interpretation of the existing bylaws. This approach helped to reduce the bureaucratic overhead necessary in drafting new laws. The official interpretation of the bylaws was to take effect on the month following the public statement. That is, beginning in February 2013.

Outcomes and Monitoring Progress

There was very little opposition to the new measures from homebuilders. They have stated that not only is the backwater valve a relatively inexpensive addition to a new home, but that the added level of protection also works as a selling feature as many of the older homes in the area do not have a valve making the newly-built homes more secure. Furthermore, interviewed contractors indicated that a backwater valve is among the best investments that can be added to a new home. Some insurers also offer discounts on the insurance premium with the addition of these valves.

Next Steps

Town officials indicated that a useful area for future work would focus on actions to encourage the installation of backwater valves in existing homes. In particular the Town may explore the idea of a by-law for property owners that conduct a major renovation to mandate installation of a backwater valve.


Link to Full Case Study

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