2.3 Flood zones

Historic floods and special intervention zones (siz)

In 2019, many municipalities in Québec, Ontario and New Brunswick experienced spring flooding. A third of the municipality of Sainte-Marthe-sur-le-Lac was flooded.

Following these events, special intervention zones (SIZ) were declared by decree to allow for better management of flood zones. The SIZ decree was applied to the areas flooded during the 2017 and 2019 spring floods, as delineated by the Government of Québec on maps posted on the website of the Ministère de l’Environnement et de la Lutte contre les changements climatiques.

Special intervention zones (SIZ) have been cancelled since March 1, 2022, but related information remains available. However, older flood zone maps continue to serve as a reference for identifying at-risk areas until the new regulatory framework currently under development comes into effect. In fact, the areas flooded during the exceptional floods in 2017 and 2019 are now part of the means used to delimit a flood zone for the application of the transitional regime.

Although a certificate of location presents the state of the immovable as of the date of its issuance, land surveyors do not automatically indicate whether a portion of an immovable was subject to the SIZ decree. In addition, it is always possible that the map has changed since the last certificate was issued. Upon request, the land surveyor can provide the topographical map required for verifying whether the lot is located in a flood zone, without necessarily issuing a certificate of location.

Verifications can also be made using the Google map on the government website https://www.cehq.gouv.qc.ca/index_en.asp.

The new regulatory framework and a new generation of mapping

Although published on June 25, 2025, the new regulatory framework will not come into effect until March 1, 2026.

The transitional regime will continue to apply until the new regulations come into effect.

The new generation of maps will be developed during this period by the Ministère de l’Environnement, de la Lutte contre les changements climatiques, de la Faune et des Parcs and its municipal partners. They will be published progressively, as they are approved, starting in March 2026.

The redefined flood zones will be categorized into four classes of potential flood intensity for a given territory, each represented by a specific colour: Very high (burgundy), High (red), Moderate (orange) and Low (yellow). A final category will be designated as a “protected area with residual risk” (red stripe) for territories located behind a recognized protective structure—such as a dyke or wall—where a risk of flooding still remains.

The classes are defined by experts using a table that combines flood probability (ranging from 100% to 7% likelihood of at least one flood in 25 years) with the potential water depth measured from ground level during a flood. 

The updated regulatory framework for water environments will determine what works and interventions are permitted in designated flood zones. Regulatory constraints, restrictions, and permissions vary according to the intensity class assigned to each area.

In the very high zone, new construction will be prohibited; however, certain renovation or adaptation work on existing buildings—such as relocating the electrical entrance or creating bedrooms on upper floors to enhance flood resistance—will be permitted. Reconstruction will be permitted in the high zone, subject to specific conditions. In the moderate zone, interventions will be more flexible but still supervised. Finally, regulatory restrictions will be more limited in the low zone.

Broker's duties

Obviously, when a building is located in a flood zone, verifications and disclosures must be carried out.

More specifically, brokers must:

• Check whether a property that is the subject of a transaction appears on the maps of the Ministère de l’Environnement or is located in a municipality designated as a special intervention zone.
• Contact the municipality concerned for further information on the applicable restrictions, notably regarding the issuance of construction permits.
• Disclose to the parties to the transaction whether the property in question has been designated as a SIZ, its flood zone classification, and whether it has ever been flooded.
• Document the steps taken.

For more information

Flooding information toolkit: A toolkit to protect the public in future transactions