Spring Melt and Water Infiltration in a Montreal Basement

In March, snow piled against a foundation melts faster than frozen ground can absorb it. The water then takes the shortest route down, and that route often runs through an opening nobody looks at in July. Here is where it gets in, what you can check from outside in fifteen minutes, and why your insurer treats an infiltration and a refoulement d’égout, a sewer backup, as two separate claims.

Where water gets in during the melt: five entry points

The City of Laval gives the simplest definition there is: when water from outside enters a building, that is water infiltration. It names three main causes: poor sealing of the foundation, of the windows or of a garage door; poor drainage of rainwater on the land around the house; and a water table close to the surface. The melt concentrates those three causes into the same month.

The five entry points:

1. The foundation, through a crack or through the joint between the wall and the slab.
2. The basement window, when its window well fills with snow.
3. The reverse slope driveway, which carries water from the street downhill.
4. The roof, under a barrage de glace, an ice dam.
5. The land itself, when the grade brings water back toward the building.

One point is deliberately missing: refoulement d’égout, which comes back up through the plumbing rather than through the building envelope. The drain, the backwater valve and the Montreal grant are covered in our article on a sagging sewer drain in Montreal. Here we stay with the water that comes from outside.

Grading: basement water infiltration starts outdoors

Grading decides almost everything. CMHC’s checklist on moisture and mould is direct: make sure the ground around the house slopes so runoff drains away from the house, and make sure the slope of the soil, the lawn and the driveway carries water away from the house. Three surfaces, not just the grass.

In Laval, the division of roles is spelled out. Correcting the flow around the building, or making the foundation watertight, is the owner’s job. The City steps in when the infiltration is caused by inadequate drainage on the public right of way, or by a water main or a storm sewer in poor condition.

The driveway that slopes down toward the house. Laval then requires a crown that keeps water from pooling near the building, at section 4.01.03 of by-law L-11870. Montreal treats the same vulnerability differently: it lists a hump behind the sidewalk, a dos d’âne en arrière-trottoir, a watertight garage door, a removable flood barrier, a batardeau amovible, and filling in the driveway as the four measures to consider.

The window well. A window well packed with snow is a reservoir sitting against an opening. The Bureau d’assurance du Canada, the Insurance Bureau of Canada, puts the action in writing in its spring thaw advice: clear the snow out of window wells and shovel snow away from the foundation. Before the first mild spell, not during it.

The roof, the ice dam, and the wall that stains underneath

A barrage de glace forms when snow melts on the warm part of the roof and refreezes near the eaves, which are colder. Water builds up behind that dam and looks for a way out sideways, under the shingles.

What that produces inside does not look like a classic roof leak. The mark appears at the top of an exterior wall or around the edge of the ceiling. CMHC restates the general mechanism: water gets into the house when there is a crack or a leak in its foundation, its floors, its walls or its roof. A brownish stain at the top of a wall, in March, deserves a question to the seller before it gets a reassuring explanation.

Hold on to the insurance vocabulary, because it changes everything in the next section: according to the Bureau d’assurance du Canada, an infiltration created by an ice dam on the roof or in the gutters falls under the above ground water avenant, the “eau au-dessus du sol” endorsement.

The gutters, and the exact spot where they discharge

This is the fastest check of a showing, and the one most often skipped. The question is not whether the house has gutters, but where they send the water.

What Laval requires. By-law L-11870 provides that water from a sloped roof carried away by gutters must be discharged onto a permeable surface on the property, lawn or flower bed, at least 1 metre from the building. The City also names the three non compliant connections: hooking into the foundation drain, discharging directly to the street, and dumping water onto an impermeable surface sloped toward the street. Redirecting the water onto the neighbour’s land is not a way out: Laval points to articles 976, 979 and 983 of the Code civil du Québec, and specifies that a dispute of that kind is not a municipal matter.

What Montreal asks for. For a home with a sloped roof, the City wants gutters that send water toward a permeable surface and that are not connected to the foundation drain. Its prevention list adds a clean, working drain at the bottom of a reverse slope driveway.

The distance. The Bureau d’assurance du Canada recommends that gutters and downspouts direct water away from the foundation, 2 metres out, with extensions where needed. CMHC says the same thing another way: install extensions on the downspouts so that water from rain and melted snow drains well away from the house.

To price those corrections alongside notary fees and transfer duties, the closing costs calculator exists for that.

Infiltration or refoulement: two avenants, and only one will answer

Here is the belief to correct. Plenty of owners think they hold “the water damage coverage”. There is not one, there are several, and they do not stand in for each other.

The base policy covers water damage caused by a plumbing fixture such as the bathtub, the washer or the water heater, and the bursting of a potable water pipe. For an infiltration, a refoulement d’égout or the overflow of a body of water, the protection has to have been added by avenant, an endorsement, with its own limit of coverage, separate from the policy’s own.

Source: Bureau d’assurance du Canada, consumer information site.

Two practical consequences. The avenant that covers you for an ice dam does not cover you for a foundation crack, and the reverse holds just as well. And in a known flood zone, coverage against the overflow of a body of water can be limited or unavailable. The numbers explain that caution: in 2024, 68% of home insurance claims paid in Quebec involved water damage, at an average cost of $23,550. Put the question to your insurer before the inspection period closes. If the answer is slow in coming, read what makes a home hard to insure.

Visiting in March: what a buyer sees and will not see in July

A melt showing is a free load test. What is visible then, and only then:

• Where water pools on the land, and which way it heads.
• The snow piled against the foundation, and how far up the wall it reaches.
• Ice at the foot of the downspouts, a sign that the water is not moving away.
• Icicles along the roof edge, which give the dam away.
• The window well full of snow, and the sealant around the window.
• Water running down the driveway toward the door rather than toward the street.
• In the basement: a fresh stain, a dehumidifier running, a musty smell near the exterior wall.

By July all of that has dried. It is the seasonal advantage set out in the blind spots of a winter purchase. None of it replaces a professional examination: the full list is in the pre-purchase inspection, item by item.

Déclarations du vendeur: what a past infiltration forces you to write down

The mandatory Déclarations du vendeur sur l’immeuble form, the seller’s declarations on the property, DV 00001, version V24 of June 2022, leaves no grey area.

• D3.6: does water accumulate periodically on the land?
• D4.1: has there ever been any water infiltration? If so, the seller ticks the location in a list that includes the basement or crawl space, the roof, the terrace, the balcony, the solarium, the skylight, the door, the window and the chimney.
• D5.2: have any problems ever affected the basement or the crawl space, including cracks in the foundation?

These questions are about what has already happened, not about what is left. An infiltration repaired in 2019 is still an infiltration to declare in 2026. On the buyer’s side, a “yes” is not a reason to run: it is a reason to ask for the invoices, the method used and the contractor’s name. The form is explained in detail in the seller’s declaration in Quebec.

Frequently asked questions

The seller says the basement has never taken water. How do I verify that? Ask for the DV 00001 form filled in and signed, not a verbal summary, then compare it against what you see at the bottom of the walls. Add a written question about past insurance claims.

My policy covers refoulement d’égout. Am I covered for a crack? Not necessarily. Infiltration through the foundation and refoulement fall under the same avenant with several insurers, but water coming in through the roof or a window falls under a different one. Have both confirmed in writing.

Do I have to clear the snow away from the foundation every winter? The Bureau d’assurance du Canada recommends it, along with clearing window wells and walkways, to give the meltwater somewhere to run.

My gutters discharge onto asphalt. Is that compliant? In Laval, no: by-law L-11870 requires a permeable surface, at least 1 metre from the building, and lists discharge onto an impermeable surface sloped toward the street among the non compliant connections. Check your own municipality’s rule, it is not uniform.

To round this out, read the pre-purchase inspection, item by item and the sagging sewer drain in Montreal.

Visiting a house during the melt and unsure about what you are seeing at the bottom of the wall? Write to me. I will tell you which questions to put in the promesse d’achat before the conditions are lifted.

Georges Matar

Residential Real Estate Broker · RE/MAX DU CARTIER INC.

Contact Georges