Foundation Cracks in Winter: Why November Is Your Last Chance to Seal Them

November is the window you don't know you're watching. Right now, before the freeze really hits, you can spend a couple of hundred dollars to keep your basement dry all winter. Wait until January and that same crack costs you $5,000 to fix and another $15,000 in water damage remediation.

We get 20 to 30 calls a month from Toronto homeowners in December with the same story. They saw the crack in September, meant to do something about it, and now water is running in the basement in 30-degree weather. By then your insulation is soaked, your drywall is growing mould, and the job is exponentially harder.

Where Toronto foundation cracks come from

Your concrete foundation cracks because concrete shrinks as it cures, and because the earth around it moves with temperature and moisture changes. In a GTA winter, that freeze-thaw cycle is relentless. Water seeps into the crack, freezes, expands, and pushes the crack wider.

Most Toronto homes have some foundation cracking. Century homes in Leslieville and the Annex have lots of it. Postwar bungalows in North York and Etobicoke show it too. Newer builds from the 1990s aren't exempt. It's not a sign your foundation is failing. It's a sign you need to seal the ones that matter.

Which cracks actually let water in

Not every crack in your foundation will flood your basement. You need to know which ones will. Here's the rule: if the crack runs vertically or diagonally, or if water can pool against it from outside, it's a problem.

• Vertical cracks: These run up and down the wall. They're structural movement, and they're the most common water path. Water finds them quickly.
• Horizontal cracks: These are less common and more serious (they usually mean structural issues). If you see a horizontal crack wider than a hairline, call a structural engineer before you worry about sealing it.
• Cracks at the foundation/wall joint: Where the basement wall meets the foundation slab is a natural water channel. Any crack there will leak, and it'll leak fast.
• Cracks in the foundation floor: If your foundation floor (the concrete pad you stand on) has cracks running toward the walls, water and moisture will wick along them into your walls and any stored items.

If water is pooling against the crack on the outside of your home (look after rain), or if you feel cool air flowing out of the crack, it's active. Seal it this month.

What happens when you don't seal them before winter

A small amount of water trickling in through a crack doesn't seem like much in November. By January it becomes a problem. Here's the timeline we see consistently across Toronto and the GTA.

Week 1 (late November, early freeze): Water seeps in slowly. Your floor is damp. You notice a faint musty smell.

Week 2 (December cold snap): The crack widens slightly from freeze-thaw. Water flow picks up. Your sump pump (if you have one) starts running more often. You see damp patches on your basement walls.

Week 3-4 (heavy cold): Mould starts growing inside walls where it's damp but you can't see it. Your insulation is retaining moisture instead of insulating. Your drywall is soft. Calling now means a $3,000 to $5,000 injection sealing job plus remediation. You're also looking at possible mould removal if it spread behind walls.

February thaw and spring melt: If the freeze breaks and warm weather arrives, rapid thawing pushes more water in and out of your foundation simultaneously. This is when you get sudden basement flooding, which now costs $15,000 to $25,000 in restoration, drywall replacement, and mould remediation.

One crack sealed in November might cost $200 to $400. That same crack in January costs $2,000 to $4,000 to seal properly. Add mould remediation and structural drying and you're north of $15,000.

How to seal foundation cracks properly

There are quick fixes and real fixes. Quick fixes fail. We clean up after them all the time.

Caulk (the temporary fix): Filling a crack with silicone caulk is a bandaid. It works for about 12 months, then it shrinks and peels away. By January it's worthless. Save your time.

Polyurethane injection (the real fix): This is what you want. A technician drills small holes along the crack (every 12 inches or so) and injects a polyurethane foam that expands to fill the crack completely. It bonds to the concrete, stays flexible through freeze-thaw cycles, and lasts 20 years. Cost in Toronto is usually $150 to $400 per crack depending on length and access. A crew does it in a few hours.

Epoxy injection: Similar process to polyurethane, but epoxy is more rigid. It works for some cracks, but it's less forgiving in freeze-thaw conditions. Polyurethane is the better choice for Canadian winters.

Interior waterproofing (if it's too late): If water is already coming in, sealing from inside can help. A crew applies a waterproof membrane and paint to stop water on the inside. This doesn't fix the crack, so water is still trying to get in from outside. You're just blocking it at the wall. Cost is $100 to $300 per linear foot of affected wall. It's expensive because it's a bigger job. This is Plan B after exterior sealing fails or if you discover the problem in December.

Finding the right cracks to seal

Go to your basement on a dry day and look carefully. Walk the perimeter. Look for hairline cracks, wider gaps, white mineral deposits (calcium and salt, signs water has been seeping), or any place where concrete is spalling (flaking or breaking apart).

Mark the ones you see with chalk or tape. If you're not sure whether a crack is active (actually letting water in) or just cosmetic, spray it with water from a hose and watch for a few hours. If moisture appears on the inside, it's active.

Don't panic if you find cracks. You probably have them. The question is which ones matter. If water isn't coming in, and you live in a newer home in Vaughan or Markham, you might only need to seal one or two. If you're in an older house in Scarborough or North York with poor exterior grading, you might need to do more work.

Why DIY doesn't work for this

Caulking a foundation crack yourself will feel productive and take three hours. It will also fail by March. Injection sealing requires drilling precise holes at the right depth, knowing which product to use, and having equipment to ensure the injection material flows all the way through the crack. It's not a DIY job.

Hire a licensed waterproofing contractor. Expect to pay $150 to $400 per crack for injection sealing. Get quotes from two contractors. Ask if they guarantee the work. A good crew will stand behind it for 5 to 10 years.

How much water damage costs if you skip this

If a crack floods your basement and water sits for more than 24 hours in winter, you're looking at:

• Water extraction and structural drying: $2,000 to $5,000
• Drywall replacement: $1,500 to $3,000 per wall
• Insulation replacement: $800 to $1,500
• Mould remediation (if growth started): $3,000 to $8,000
• Flooring replacement (if affected): $2,000 to $6,000
• Total: $10,000 to $25,000+

In contrast, sealing five active foundation cracks in November costs $1,000 to $2,000 total and prevents almost all of that.

One more thing

Foundation sealing is preventative work that most homeowners skip because it doesn't seem urgent. Until it is. We see more preventable water damage in Toronto from neglected foundation cracks than from any other single cause. Most of these calls come between December and February.

You have six weeks. Walk your basement, mark the cracks, and call a waterproofing crew. It's one of the smartest investments you can make before winter hits hard.

If you're in Toronto or the GTA and you want a professional look at your foundation, or if you already have water coming in through cracks, call The Preferred Group at 647-563-9966. We can assess the damage and talk about what's worth fixing before winter and what can wait.