Rainwater and flood zones in Pierrefonds-Roxboro
Updated September 28, 2026
On June 20, 2026, the torrential rain flooded homes in Pierrefonds-Roxboro even in an area far from the Rivière des Prairies, one outside the recognized flood zones. According to the borough mayor, water came up through the water table and seeped in through foundation cracks. That seepage, like sewer backup, is not part of the check, which looks at rain running off the surface.
Pierrefonds-Roxboro is a borough of the City of Montréal, whose rules apply for rain: a mandatory backwater valve on basement plumbing fixtures, and no gutter connected to the foundation drain or aimed at the street. The City also offers home inspections and RénoPlex subsidies for flood-protection work.
Heavy rain events
What public sources report about heavy rain in Pierrefonds-Roxboro, at sector level.
According to the City of Montréal, a nearly stationary line of storms dropped on the order of 150 mm of rain in 24 hours on several parts of the West Island. On already saturated ground, it contributed to rapid flooding. Several municipal buildings in the borough had minor flooding and closed. Radio-Canada reported that the Montréal fire department named the borough among the hardest-hit areas. The borough mayor said that in an area far from the river, water came up through the water table; the sources do not say what share came from sewer backup.
Sources: Ville de Montréal, Pluies diluviennes : état de situation · Radio-Canada, 21 juin 2026 · La Presse, 22 juin 2026
During the remnants of Debby, which dropped more than 150 mm in 24 hours on Greater Montréal according to the Communauté métropolitaine de Montréal, residents of the borough were hit. La Presse does not say how the water entered homes. In June 2026, the borough mayor said the people flooded that month were the same ones flooded in 2024.
Sources: La Presse, 19 août 2024 · Communauté métropolitaine de Montréal, communiqué de décembre 2025 · La Presse, 21 juin 2026
Good to know in Pierrefonds-Roxboro
- To find low spots, the City of Montréal points to the agglomeration's climate-hazard vulnerability map and its “Identification des cuvettes 2021” layer, which shows naturally low-lying areas where surface water can collect in torrential rain. (Ville de Montréal, Comment protéger son bâtiment face aux fortes pluies)
- The City of Montréal considers a house with a reverse-slope driveway, down to a garage below street level, more vulnerable when water pools on the road. It suggests a hump behind the sidewalk, a watertight garage door, filling in the driveway or a removable flood barrier. (Ville de Montréal, Comment protéger son bâtiment face aux fortes pluies)
- Montréal by-law 11-010 on protecting buildings against sewer backup makes a backwater valve mandatory on basement plumbing fixtures. Since 2011, every new building in Montréal must have them. (Ville de Montréal, Clapet antiretour)
- In Montréal, connecting a gutter to the foundation drain or aiming it at a hard surface or the street is prohibited. The City recommends sending it, and any rain-barrel overflow, to a lawn or flower bed at least 1.5 m from the foundation. (Ville de Montréal, Gouttières extérieures)
- Through the RénoPlex program, the City of Montréal subsidizes, subject to conditions, flood-protection work in houses and small buildings, such as a normally closed backwater valve or a sump pit with a pump. (Ville de Montréal, Clapet antiretour)
- The City of Montréal offers a home inspection to prevent sewer backup: automatic after a claim to the City, otherwise by waiting list, sometimes several months long. The inspector gives a report listing the corrective work; the City does not pay for that work. (Ville de Montréal, Inspection à domicile pour prévenir un refoulement d'égout)
Rivers and lakes: what the check does not cover
Waterways in Pierrefonds-Roxboro: Rivière des Prairies.
In the spring of 2017, the Rivière des Prairies flood hit a riverside area of the borough hard; a temporary dike went up on May 11, after homes had already flooded. In 2019, the river rose higher than in 2017, but the dikes built in between reduced the number of people affected. The river also backed up into the storm sewers and flooded part of boulevards de Pierrefonds and Gouin for days.
The borough asks residents flooded in 2017 or 2019, by the river, the water table or through the basement, to consider themselves in a flood zone.
Sources: Ville de Montréal, À propos de Pierrefonds-Roxboro · Radio-Canada, 8 mars 2018 · La Presse, 28 avril 2019 · La Presse, 1er mai 2019 · Ville de Montréal, Crue printanière à Pierrefonds-Roxboro
The check is about the rain that falls on the area and runs off over the ground. River and lake flooding is not part of it: in the simulation, a nearby river or lake holds no water. For a waterfront property, the official map comes first.
What we know about the ground in Pierrefonds-Roxboro
These values come from the public sources the check uses. They describe the area, not an address.
| 1 m terrain model (NRCan HRDEM) | Available across the whole area |
|---|---|
| Nearest rainfall gauge (ECCC) | Sainte-Dorothée (Laval), 7.9 km awayLocal rainfall statistics. |
| Municipal street drains | Modelled, from the open municipal catch-basin inventory |
| Mapped culverted road crossings | 37Culvert lines mapped in OpenStreetMap (ODbL). |
Data Source: Environment and Climate Change Canada, Short Duration Rainfall Intensity-Duration-Frequency Data, used under the ECCC Data Servers End-use Licence.
Area analysed: administrative boundaries of the Montréal agglomeration, Ville de Montréal, CC BY 4.0 licence.
Probed on September 28, 2026.
The official map and what it does not show
Québec's flood-zone maps cover rivers and lakes. They do not show rain water collecting on a lot, in a low spot or at the bottom of a sloping driveway. Check the official map for the address first: it is what says whether a property is in a flood zone.
- Spring flooding in Pierrefonds-Roxboro (City of Montréal)
- Check a property on the Government of Québec site (in French)
FloodVerity does not reproduce these maps and does not state any regulatory zone.
Check an address in Pierrefonds-Roxboro for $39
We drop a 100-year, one-hour design storm on the ground around the property, route the runoff, and email you the peak depth of rain water at the address, where it collects, a map and a 3D view.
What the check does not do
- This check models rain falling on the area itself and running off over the terrain. Water arriving from a river or lake, sewer backup, ice jams and storm surge are not modelled.
- The pipe network itself, roof and lot drainage, and sewer backup are not modelled.
- Where the structures inventory records a culverted road crossing, it is lowered to a partly blocked opening rather than solved hydraulically.
- It does not replay the storms described on this page: it applies a 100-year, one-hour design storm.
- It is a screening: a simulated storm on public terrain data, not a hydraulic study, not an official flood-zone determination, not an insurance opinion.
Notaries and brokers in Pierrefonds-Roxboro
We run the same check over a list of addresses and deliver a spreadsheet ranking them by the modelled rain depth. Priced per address, on quote.
Email [email protected]Other towns and areas
The FloodVerity check is a screening: it applies a design rainstorm to public terrain data and simulates where the rain runs and collects. It is not a hydraulic study or an official flood-zone determination, and it covers neither river and lake flooding nor sewer backup.