Summary of potential building vulnerabilities during heavy rain and key adaptation measures to protect against back-up and flooding.

Checklist 

All building types 

• Check your home for entry points that may facilitate water surging in from the street, such as a downstairs entrance. 
• Make sure you have properly working check valves (also known as backwater valves or backflow preventers) on plumbing fixtures located below street level. It is essential that there is a check valve for all drains on the floor or for plumbing equipment (for example: toilets, taps, etc.) 
• If possible, clear debris that could block the entry of water from the sump on the street near your residence in order to facilitate the collection of surface runoff. 
• In the basement, make sure floor drains are clear and valuables are in watertight containers. 
• Make sure that the openings in the building are watertight. For doors and windows located under or at street level, there are a number of permanent or temporary protection measures on the market that help reduce the risk of being flooded, such as watertight partitions and removable cofferdams, etc. 

For small and medium-sized residential buildings: 

This type of home is more vulnerable to flooding when water accumulates on the roadway, because the entrance is located below street level. As a result, water can enter the building more easily. Here are the three main protective measures to consider:

• If the risk of water accumulating on the street is low, adding a speed bump at the top of the downstairs entrance may be enough to prevent water from the street from diverting toward the entry, if the slope allows.
• Installing a watertight garage door, and an adjoining entrance door, if applicable, is a measure that has been successfully tested in Montréal. It may provide effective protection against the risk of flooding and let you keep your garage.
• Backfilling the entry is a measure that definitely eliminates the risk of surface flooding. You should, however, check with your borough to find out the current regulations and requirements in effect.

These three measures are eligible for financial support from the city under the RenoPlex program.

Homes with sloped roofs 

• Gutters must send water to a permeable surface and must not be connected to the foundation drain. 

Plex buildings 

It’s possible that there may only be one indoor pipe that routes both domestic water and rainwater from the flat roof. This type of pipe presents a risk of water overflowing from plumbing fixtures upstairs during a severe thunderstorm. 

It is recommended that you separate the rainline from the flat roof by following these recommendations from the Régie du bâtiment du Québec (in French).

Vulnerability map 

You can view the Montréal agglomeration climate risk vulnerability map (in French) l and select the “Identification des cuvettes 2021” (2021 Basin Identification) map. This map identifies areas whose naturally sunken topography has the potential for surface water accumulation during heavy rains. 

Tangible actions for a safer future 

Montréal has set out 10 key measures to adapt to torrential rains in its action plan for flood resilience during heavy rains. One of the components of this plan includes support measures for owners to increase the resilience of their building. In particular, the city is committed to offering advisory services to owners on how to best protect their building against floods. In addition, Montréal is actively collaborating with a number of organizations and institutions to document and test various protection measures on private property, to ensure that they can effectively reduce the risk of flooding.

Subsidy program 

Do you have to carry out potentially expensive renovations to adapt your building? Montréal’s RenoPlex program offers a subsidy for certain types of renovation that help reduce the risk of flooding. Check the criteria and eligibility of your renovation project.

Other resources

1. Écohabitation
2. Régie du bâtiment du Québec