- Thin vertical or diagonal cracks in a poured concrete wall are usually shrinkage cracks. They aren't structural, but they can leak, and injection seals them from inside.
- Horizontal cracks, stair-step cracks in block, and cracks wider at one end point to soil pressure or settlement and need a structural look.
- Cracks a quarter inch wide or wider, or ones that keep growing, deserve a professional assessment.
- Fixing the crack without fixing the cause, whether that's water, soil pressure or a settling footing, just means fixing it again later.
Is a crack in a basement wall normal?
Usually, yes. Concrete shrinks as it cures, and that shrinkage has to go somewhere. Tarion's construction guidelines, which set the standard for new homes in Ontario, say it plainly: concrete walls naturally crack during curing due to shrinkage. A thin crack of even width in a poured wall is the most common thing we see in a basement, and on its own it isn't a structural concern.
What makes a crack a problem is one of three things: it leaks, it's still moving, or its shape points to a force acting on the wall. The rest of this guide is about telling those apart.
Types of basement wall cracks and what they mean
| Crack | Where you see it | Usually means | Concern |
|---|---|---|---|
| Hairline vertical | Poured concrete walls | Shrinkage as the concrete cured | Low. Seal it if it leaks |
| Diagonal, even width | Poured concrete walls | Shrinkage | Low. Seal it if it leaks |
| Diagonal, wider at one end | Poured or block walls | Settlement, especially if wider at the bottom | Moderate to high |
| Stair-step | Block walls and brick, along the mortar joints | Settlement or wall movement | Moderate to high |
| Horizontal | Block walls, partway up | Soil pressure from outside: poor backfill, saturated or frozen soil | High. The wall can bow |
| Floor cracks | The concrete slab | Usually shrinkage | Low, unless one side has lifted |
Based on home inspector guidance. A guide, not a diagnosis.
How wide is too wide?
Width is a useful clue, though not the whole story. For new homes, Tarion treats poured-wall cracks over 6 mm, block-wall cracks over 2 mm and basement floor cracks over 4 mm as unacceptable. Home inspector guidance from InterNACHI suggests that any crack a quarter inch wide or wider may point to a serious problem that a licensed engineer should evaluate.
Direction and movement matter just as much. A wide shrinkage crack that hasn't changed in years is less worrying than a thin horizontal crack that's opening up.
- Mark both ends of the crack with a pencil line and the date.
- Measure the width at its widest point with a ruler or crack gauge.
- Take a photo with a coin beside it for scale.
- Check again every month or two, through a full year of seasons.
If a crack grows past your pencil marks or gets wider, it's still moving and needs a professional look.
Why basement wall cracks leak
The soil around a foundation holds water. When it's saturated, in the spring thaw or after a heavy storm, that water builds up pressure against the wall. The National Research Council's guidance on basement walls describes it forcing water through joints and cracks, and CMHC notes basement leaks are most likely during a rapid spring thaw or heavy rain.
That's why a crack can stay bone dry all summer and run every April. The crack hasn't changed. The water pressure behind it has.
Anything that puts more water against the wall makes it worse: short downspouts, ground that slopes toward the house, window wells without drains, and old weeping tile that's clogged. Fixing those lowers the pressure behind every crack in the wall, not just the one you can see.
Fixing cracks in a foundation: the options
The right repair depends on what kind of wall you have, what the crack is doing and why it formed.
- Polyurethane injection for leaking, non-structural cracks in poured walls. It expands to fill the crack and seal out water. Typically $500 to $1,000 per crack.
- Epoxy injection where the two sides of the crack need bonding back together.
- Epoxy plus carbon fibre staples for cracks that are moving or widening, typically $1,000 to $3,000 per crack.
- Exterior repair, digging down to the crack and sealing it from outside, when the inside can't be reached. Typically $1,400 to $3,000 per crack.
- Wall reinforcement for a horizontal crack with a bowing wall: carbon fibre straps or steel beams, or a rebuild if it has moved too far.
- Stabilizing the footing for settlement cracks, usually by underpinning. See our settling foundation guide.
Prices are typical Hamilton-area ranges before tax. For the full breakdown, read our foundation crack repair cost guide.
Basement foundation crack repair by wall type
Poured concrete walls are what injection was made for. A crack in a solid wall is a single clean path, so resin pumped into it fills it through the full thickness.
Block walls are different. They're built from hollow units held together with mortar, so cracks follow the joints and water travels through the hollow cores. A leaking or cracked block wall usually needs block repair, drainage or reinforcement rather than injection.
Stone foundations, common in century homes, leak through mortar that has worn away over decades. They're repointed and waterproofed rather than injected. See stone foundation repair for how that works.
Can you fix a basement wall crack yourself?
For a small, dry shrinkage crack you just want to keep an eye on, there's nothing to fix. For a leaking one, DIY kits exist, but a surface patch of hydraulic cement or caulking only closes the face of the wall. Water under pressure goes around it.
Injection kits sold for DIY use can work on a simple crack if the instructions are followed closely. Don't attempt a structural crack yourself, and if your home is still under warranty, report the crack to your builder before anyone changes it. Tarion covers water getting in through the basement walls for two years, and major cracks under the seven-year structural warranty.
When to call a professional
- The crack is horizontal, or the wall looks pushed in.
- It's a stair-step crack in a block wall or your brick.
- It's a quarter inch wide or wider, or wider at one end than the other.
- One side of the crack sits proud of the other.
- It's growing past your pencil marks.
- Doors are sticking or floors are sloping as well.
- It leaks, even only in the spring.
Not sure? Text a photo to (289) 880-7988 and we'll usually give you a straight read before anyone comes out. If it's only cosmetic, we'll tell you that too. If it's structural, our sister company AVH Foundations handles bowing and cracked wall repair.
Basement wall crack questions
Should I worry about a hairline crack in my basement wall?
Is a horizontal crack in a basement wall serious?
Can a cracked foundation be fixed?
Will a crack in my basement wall get worse?
Does a new home warranty cover basement wall cracks?
How Basement Worx repairs cracks
Related guides
AVH Foundations handles steel bracing, rebuilds, settling and underpinning. Same family, one visit to assess both.
Basement Worx works across Hamilton, Burlington, Oakville, Milton, Ancaster, Dundas, Stoney Creek, Waterdown, Cambridge, Brantford, Caledonia and Grimsby.